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       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.

NAME

       ex — text editor

SYNOPSIS

       ex [-rR] [-s|-v] [-c command] [-t tagstring] [-w size] [file...]

DESCRIPTION

       The  ex  utility  is a line-oriented text editor. There are two other modes of the editor—
       open and visual—in which screen-oriented editing is  available.  This  is  described  more
       fully by the ex open and visual commands and in vi.

       If an operand is '-', the results are unspecified.

       This  section  uses the term edit buffer to describe the current working text. No specific
       implementation is implied by this term. All editing changes  are  performed  on  the  edit
       buffer,  and  no  changes  to  it shall affect any file until an editor command writes the
       file.

       Certain terminals do not have all the capabilities necessary to support  the  complete  ex
       definition,  such  as  the  full-screen editing commands (visual mode or open mode).  When
       these commands cannot be supported on such terminals, this condition shall not produce  an
       error  message  such  as  ``not  an  editor  command''  or  report  a  syntax  error.  The
       implementation may either accept the commands and produce results on the screen  that  are
       the  result  of  an  unsuccessful  attempt  to  meet  the  requirements  of this volume of
       POSIX.1‐2017 or report an error describing the terminal-related deficiency.

OPTIONS

       The ex utility shall conform to the Base Definitions volume of POSIX.1‐2017, Section 12.2,
       Utility  Syntax  Guidelines,  except for the unspecified usage of '-', and that '+' may be
       recognized as an option delimiter as well as '-'.

       The following options shall be supported:

       -c command
                 Specify an initial command to be executed in the first edit buffer  loaded  from
                 an  existing  file  (see the EXTENDED DESCRIPTION section).  Implementations may
                 support more than a single -c option. In  such  implementations,  the  specified
                 commands shall be executed in the order specified on the command line.

       -r        Recover  the  named  files  (see  the  EXTENDED  DESCRIPTION section).  Recovery
                 information for a file shall be saved during an  editor  or  system  crash  (for
                 example,  when the editor is terminated by a signal which the editor can catch),
                 or after the use of an ex preserve command.

                 A crash in this context is an unexpected failure of the system or  utility  that
                 requires  restarting  the  failed system or utility. A system crash implies that
                 any utilities running at the time also crash. In the case of an editor or system
                 crash,  the number of changes to the edit buffer (since the most recent preserve
                 command) that will be recovered is unspecified.

                 If no file operands are given and the -t option  is  not  specified,  all  other
                 options,  the  EXINIT  variable, and any .exrc files shall be ignored; a list of
                 all recoverable files available to the invoking user shall be written,  and  the
                 editor shall exit normally without further action.

       -R        Set readonly edit option.

       -s        Prepare ex for batch use by taking the following actions:

                  *  Suppress writing prompts and informational (but not diagnostic) messages.

                  *  Ignore  the  value  of TERM and any implementation default terminal type and
                     assume the terminal is a type incapable of supporting open or visual  modes;
                     see the visual command and the description of vi.

                  *  Suppress  the  use of the EXINIT environment variable and the reading of any
                     .exrc file; see the EXTENDED DESCRIPTION section.

                  *  Suppress autoindentation, ignoring the value of the autoindent edit option.

       -t tagstring
                 Edit the file containing the specified tagstring; see ctags.  The  tags  feature
                 represented  by  -t  tagstring  and  the  tag  command  is optional. It shall be
                 provided on any system that also provides a conforming implementation of  ctags;
                 otherwise,  the use of -t produces undefined results. On any system, it shall be
                 an error to specify more than a single -t option.

       -v        Begin in visual mode (see vi).

       -w size   Set the value of the window editor option to size.

OPERANDS

       The following operand shall be supported:

       file      A pathname of a file to be edited.

STDIN

       The standard input consists of a series of commands and input text, as  described  in  the
       EXTENDED  DESCRIPTION section. The implementation may limit each line of standard input to
       a length of {LINE_MAX}.

       If the standard input is not a terminal device, it shall be as if the -s option  had  been
       specified.

       If  a  read  from the standard input returns an error, or if the editor detects an end-of-
       file condition from the standard input, it shall be equivalent to  a  SIGHUP  asynchronous
       event.

INPUT FILES

       Input files shall be text files or files that would be text files except for an incomplete
       last line that is not longer than  {LINE_MAX}-1  bytes  in  length  and  contains  no  NUL
       characters.  By default, any incomplete last line shall be treated as if it had a trailing
       <newline>.  The editing  of  other  forms  of  files  may  optionally  be  allowed  by  ex
       implementations.

       The  .exrc  files  and source files shall be text files consisting of ex commands; see the
       EXTENDED DESCRIPTION section.

       By default, the editor shall read lines from the files to be edited  without  interpreting
       any of those lines as any form of editor command.

ENVIRONMENT VARIABLES

       The following environment variables shall affect the execution of ex:

       COLUMNS   Override  the  system-selected  horizontal screen size. See the Base Definitions
                 volume of POSIX.1‐2017, Chapter 8, Environment Variables for  valid  values  and
                 results when it is unset or null.

       EXINIT    Determine  a  list  of ex commands that are executed on editor start-up. See the
                 EXTENDED DESCRIPTION section for more details of the initialization phase.

       HOME      Determine a pathname of a directory that shall be searched for an editor  start-
                 up file named .exrc; see the EXTENDED DESCRIPTION section.

       LANG      Provide a default value for the internationalization variables that are unset or
                 null.  (See  the  Base  Definitions  volume  of   POSIX.1‐2017,   Section   8.2,
                 Internationalization   Variables  for  the  precedence  of  internationalization
                 variables used to determine the values of locale categories.)

       LC_ALL    If set to a non-empty string  value,  override  the  values  of  all  the  other
                 internationalization variables.

       LC_COLLATE
                 Determine the locale for the behavior of ranges, equivalence classes, and multi-
                 character collating elements within regular expressions.

       LC_CTYPE  Determine the locale for the interpretation of sequences of bytes of  text  data
                 as  characters  (for example, single-byte as opposed to multi-byte characters in
                 arguments and input files), the behavior of  character  classes  within  regular
                 expressions, the classification of characters as uppercase or lowercase letters,
                 the case conversion of letters, and the detection of word boundaries.

       LC_MESSAGES
                 Determine the locale that should be used to affect the format  and  contents  of
                 diagnostic messages written to standard error.

       LINES     Override  the  system-selected vertical screen size, used as the number of lines
                 in a screenful and the vertical screen  size  in  visual  mode.   See  the  Base
                 Definitions  volume  of POSIX.1‐2017, Chapter 8, Environment Variables for valid
                 values and results when it is unset or null.

       NLSPATH   Determine the location of message catalogs for the processing of LC_MESSAGES.

       PATH      Determine the search path for the shell  command  specified  in  the  ex  editor
                 commands  !, shell, read, and write, and the open and visual mode command !; see
                 the description of command search and  execution  in  Section  2.9.1.1,  Command
                 Search and Execution.

       SHELL     Determine the preferred command line interpreter for use as the default value of
                 the shell edit option.

       TERM      Determine the name of the terminal type. If this variable is unset or  null,  an
                 unspecified default terminal type shall be used.

ASYNCHRONOUS EVENTS

       The  following  term  is  used  in  this  and  following  sections  to specify command and
       asynchronous event actions:

       complete write
                 A complete write is a write of the entire contents of the edit buffer to a  file
                 of  a type other than a terminal device, or the saving of the edit buffer caused
                 by the user executing the ex preserve command. Writing the contents of the  edit
                 buffer  to a temporary file that will be removed when the editor exits shall not
                 be considered a complete write.

       The following actions shall be taken upon receipt of signals:

       SIGINT    If the standard input is not a terminal device, ex shall not write the  file  or
                 return  to  command  or  text  input  mode,  and shall exit with a non-zero exit
                 status.

                 Otherwise, if executing an open or visual text input mode command, ex in receipt
                 of SIGINT shall behave identically to its receipt of the <ESC> character.

                 Otherwise:

                  1. If  executing  an ex text input mode command, all input lines that have been
                     completely entered shall be resolved into the edit buffer, and any partially
                     entered line shall be discarded.

                  2. If there is a currently executing command, it shall be aborted and a message
                     displayed. Unless otherwise specified by the ex or vi command  descriptions,
                     it is unspecified whether any lines modified by the executing command appear
                     modified, or as they were before being modified by the executing command, in
                     the buffer.

                     If  the  currently  executing  command  was a motion command, its associated
                     command shall be discarded.

                  3. If in open or visual command mode, the terminal shall be alerted.

                  4. The editor shall then return to command mode.

       SIGCONT   The screen shall be refreshed if in open or visual mode.

       SIGHUP    If the edit buffer has been modified since the last  complete  write,  ex  shall
                 attempt  to  save the edit buffer so that it can be recovered later using the -r
                 option or the ex recover command. The editor shall not write the file or  return
                 to command or text input mode, and shall terminate with a non-zero exit status.

       SIGTERM   Refer to SIGHUP.

       The action taken for all other signals is unspecified.

STDOUT

       The  standard output shall be used only for writing prompts to the user, for informational
       messages, and for writing lines from the file.

STDERR

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES

       The output from ex shall be text files.

EXTENDED DESCRIPTION

       Only the ex mode of the editor is described in this section. See vi for additional editing
       capabilities available in ex.

       When  an  error occurs, ex shall write a message. If the terminal supports a standout mode
       (such as inverse video), the message shall be written in standout mode.  If  the  terminal
       does  not  support a standout mode, and the edit option errorbells is set, an alert action
       shall precede the error message.

       By default, ex shall start in command mode, which shall be indicated by a  :  prompt;  see
       the  prompt  command.  Text  input  mode  can  be entered by the append, insert, or change
       commands; it can be exited (and command mode re-entered) by typing a <period> ('.')  alone
       at the beginning of a line.

   Initialization in ex and vi
       The  following symbols are used in this and following sections to specify locations in the
       edit buffer:

       alternate and current pathnames
             Two pathnames, named current and alternate, are maintained by  the  editor.  Any  ex
             commands that take filenames as arguments shall set them as follows:

              1. If  a  file argument is specified to the ex edit, ex, or recover commands, or if
                 an ex tag command replaces the contents of the edit buffer.

                  a. If the command replaces  the  contents  of  the  edit  buffer,  the  current
                     pathname shall be set to the file argument or the file indicated by the tag,
                     and the alternate pathname shall be set to the previous value of the current
                     pathname.

                  b. Otherwise, the alternate pathname shall be set to the file argument.

              2. If a file argument is specified to the ex next command:

                  a. If  the  command  replaces  the  contents  of  the  edit buffer, the current
                     pathname shall be set to the first file argument, and the alternate pathname
                     shall be set to the previous value of the current pathname.

              3. If  a  file  argument  is specified to the ex file command, the current pathname
                 shall be set to the file argument, and the alternate pathname shall  be  set  to
                 the previous value of the current pathname.

              4. If a file argument is specified to the ex read and write commands (that is, when
                 reading or writing a file, and not to  the  program  named  by  the  shell  edit
                 option), or a file argument is specified to the ex xit command:

                  a. If  the  current pathname has no value, the current pathname shall be set to
                     the file argument.

                  b. Otherwise, the alternate pathname shall be set to the file argument.

             If the alternate pathname is set to the previous value of the current pathname  when
             the  current  pathname had no previous value, then the alternate pathname shall have
             no value as a result.

       current line
             The line of the edit buffer referenced  by  the  cursor.  Each  command  description
             specifies  the current line after the command has been executed, as the current line
             value.  When the edit buffer contains no lines, the current line shall be zero;  see
             Addressing in ex.

       current column
             The  current  display  line  column  occupied  by  the cursor. (The columns shall be
             numbered beginning at 1.) Each command  description  specifies  the  current  column
             after  the command has been executed, as the current column value. This column is an
             ideal column that is remembered over the lifetime of the editor. The actual  display
             line  column  upon  which the cursor rests may be different from the current column;
             see the cursor positioning discussion in Command Descriptions in vi.

       set to non-<blank>
             A description for a current column value, meaning that the current column  shall  be
             set  to  the  last  display  line column on which is displayed any part of the first
             non-<blank> of the line. If the line has no  non-<blank>  non-<newline>  characters,
             the  current  column  shall  be  set  to  the  last  display line column on which is
             displayed any part of the last non-<newline> character in the line. If the  line  is
             empty, the current column shall be set to column position 1.

       The  length  of  lines  in the edit buffer may be limited to {LINE_MAX} bytes. In open and
       visual mode, the length of lines in the edit buffer  may  be  limited  to  the  number  of
       characters  that  will  fit in the display. If either limit is exceeded during editing, an
       error message shall be written. If either limit is exceeded by a line read in from a file,
       an error message shall be written and the edit session may be terminated.

       If  the  editor  stops  running  due to any reason other than a user command, and the edit
       buffer has been modified since the last complete write, it shall be equivalent to a SIGHUP
       asynchronous event. If the system crashes, it shall be equivalent to a SIGHUP asynchronous
       event.

       During initialization (before the first file is copied into the edit buffer  or  any  user
       commands from the terminal are processed) the following shall occur:

        1. If  the  environment  variable EXINIT is set, the editor shall execute the ex commands
           contained in that variable.

        2. If the EXINIT variable is not set, and all of the following are true:

            a. The HOME environment variable is not null and not empty.

            b. The file .exrc in the directory referred to by the HOME environment variable:

                i.  Exists

               ii.  Is owned by the same user ID as the real  user  ID  of  the  process  or  the
                    process has appropriate privileges

               iii. Is not writable by anyone other than the owner

           the editor shall execute the ex commands contained in that file.

        3. If and only if all of the following are true:

            a. The current directory is not referred to by the HOME environment variable.

            b. A command in the EXINIT environment variable or a command in the .exrc file in the
               directory referred to by the HOME environment  variable  sets  the  editor  option
               exrc.

            c. The .exrc file in the current directory:

                i.  Exists

               ii.  Is owned by the same user ID as the real user ID of the process, or by one of
                    a set of implementation-defined user IDs

               iii. Is not writable by anyone other than the owner

           the editor shall attempt to execute the ex commands contained in that file.

       Lines in any .exrc file that are blank lines shall be ignored. If any .exrc  file  exists,
       but is not read for ownership or permission reasons, it shall be an error.

       After  the  EXINIT variable and any .exrc files are processed, the first file specified by
       the user shall be edited, as follows:

        1. If the user specified the -t option, the effect shall be as if the ex tag command  was
           entered  with  the  specified argument, with the exception that if tag processing does
           not result in a file to edit, the effect shall be as described in step 3. below.

        2. Otherwise, if the user specified any command line file arguments, the effect shall  be
           as  if  the  ex edit command was entered with the first of those arguments as its file
           argument.

        3. Otherwise, the effect shall  be  as  if  the  ex  edit  command  was  entered  with  a
           nonexistent filename as its file argument. It is unspecified whether this action shall
           set the current pathname. In an implementation where this  action  does  not  set  the
           current  pathname,  any  editor command using the current pathname shall fail until an
           editor command sets the current pathname.

       If the -r option was specified, the first time a file in the initial argument  list  or  a
       file  specified  by  the  -t option is edited, if recovery information has previously been
       saved about it, that information shall be recovered and the editor shall behave as if  the
       contents of the edit buffer have already been modified. If there are multiple instances of
       the file to be recovered,  the  one  most  recently  saved  shall  be  recovered,  and  an
       informational  message  that there are previous versions of the file that can be recovered
       shall be written. If no recovery information about a file is available,  an  informational
       message to this effect shall be written, and the edit shall proceed as usual.

       If  the  -c  option  was specified, the first time a file that already exists (including a
       file that might not exist but for which recovery information is  available,  when  the  -r
       option  is specified) replaces or initializes the contents of the edit buffer, the current
       line shall be set to the last line of the edit buffer, the current column shall be set  to
       non-<blank>,  and  the ex commands specified with the -c option shall be executed. In this
       case, the current line and current column shall not be set as described  for  the  command
       associated with the replacement or initialization of the edit buffer contents. However, if
       the -t option or a tag command is associated with this  action,  the  -c  option  commands
       shall be executed and then the movement to the tag shall be performed.

       The current argument list shall initially be set to the filenames specified by the user on
       the command line. If no filenames are specified by the user,  the  current  argument  list
       shall  be  empty.  If  the -t option was specified, it is unspecified whether any filename
       resulting from tag processing shall be prepended to the current argument list. In the case
       where the filename is added as a prefix to the current argument list, the current argument
       list reference shall be set to that filename. In the case where the filename is not  added
       as  a  prefix  to  the  current  argument  list, the current argument list reference shall
       logically be located before the first of the filenames specified on the command line  (for
       example,  a  subsequent  ex  next  command  shall edit the first filename from the command
       line). If the -t option was not specified, the current argument list reference shall be to
       the first of the filenames on the command line.

   Addressing in ex
       Addressing in ex relates to the current line and the current column; the address of a line
       is its 1-based line number, the address  of  a  column  is  its  1-based  count  from  the
       beginning of the line. Generally, the current line is the last line affected by a command.
       The current line number is the address of the current line. In each  command  description,
       the effect of the command on the current line number and the current column is described.

       Addresses are constructed as follows:

        1. The character '.'  (period) shall address the current line.

        2. The character '$' shall address the last line of the edit buffer.

        3. The positive decimal number n shall address the nth line of the edit buffer.

        4. The  address  "'x"  refers  to the line marked with the mark name character 'x', which
           shall be a lowercase letter from the portable character set, the backquote  character,
           or the single-quote character. It shall be an error if the line that was marked is not
           currently present in the edit buffer or the mark has not been set. Lines can be marked
           with the ex mark or k commands, or the vi m command.

        5. A regular expression enclosed by <slash> characters ('/') shall address the first line
           found by searching forwards from the line following the current line toward the end of
           the  edit  buffer  and  stopping  at  the  first line for which the line excluding the
           terminating <newline> matches the regular expression. As stated in Regular Expressions
           in  ex,  an  address  consisting  of  a  null  regular expression delimited by <slash>
           characters ("//") shall address the  next  line  for  which  the  line  excluding  the
           terminating  <newline>  matches  the last regular expression encountered. In addition,
           the second <slash> can be omitted at the end of a command line. If the  wrapscan  edit
           option  is  set,  the search shall wrap around to the beginning of the edit buffer and
           continue up to and including the current line, so  that  the  entire  edit  buffer  is
           searched.  Within  the regular expression, the sequence "\/" shall represent a literal
           <slash> instead of the regular expression delimiter.

        6. A regular expression enclosed in <question-mark> characters ('?')  shall  address  the
           first  line  found  by  searching  backwards  from the line preceding the current line
           toward the beginning of the edit buffer and stopping at the first line for  which  the
           line  excluding  the  terminating <newline> matches the regular expression. An address
           consisting of a null regular expression delimited by <question-mark> characters ("??")
           shall address the previous line for which the line excluding the terminating <newline>
           matches the last regular expression encountered. In addition,  the  second  <question-
           mark> can be omitted at the end of a command line. If the wrapscan edit option is set,
           the search shall wrap around from the beginning of the edit buffer to the end  of  the
           edit buffer and continue up to and including the current line, so that the entire edit
           buffer is searched. Within the regular expression, the sequence "\?" shall represent a
           literal <question-mark> instead of the RE delimiter.

        7. A  <plus-sign>  ('+')  or  a  <hyphen-minus>  ('-') followed by a decimal number shall
           address the current line plus or minus the number. A '+' or  '-'  not  followed  by  a
           decimal number shall address the current line plus or minus 1.

       Addresses  can  be followed by zero or more address offsets, optionally <blank>-separated.
       Address offsets are constructed as follows:

        1. A '+' or '-' immediately followed  by  a  decimal  number  shall  add  (subtract)  the
           indicated  number  of  lines  to  (from)  the  address. A '+' or '-' not followed by a
           decimal number shall add (subtract) 1 to (from) the address.

        2. A decimal number shall add the indicated number of lines to the address.

       It shall not be an error for an intermediate address value to be less than zero or greater
       than the last line in the edit buffer. It shall be an error for the final address value to
       be less than zero or greater than the last line in the edit buffer.

       Commands take zero, one, or two addresses; see the descriptions  of  1addr  and  2addr  in
       Command Descriptions in ex.  If more than the required number of addresses are provided to
       a command that requires zero addresses, it shall be an error. Otherwise, if more than  the
       required  number  of  addresses  are  provided to a command, the addresses specified first
       shall be evaluated and then discarded until the maximum number of valid addresses remain.

       Addresses shall be separated from each other by a <comma> (',') or  a  <semicolon>  (';').
       If no address is specified before or after a <comma> or <semicolon> separator, it shall be
       as if the address of the current line was specified before or after the separator. In  the
       case  of  a  <semicolon>  separator,  the  current  line  ('.')  shall be set to the first
       address, and only then will the next address be calculated. This feature can  be  used  to
       determine the starting line for forwards and backwards searches (see rules 5. and 6.).

       A <percent-sign> ('%') shall be equivalent to entering the two addresses "1,$".

       Any  delimiting  <blank>  characters  between  addresses,  address  separators, or address
       offsets shall be discarded.

   Command Line Parsing in ex
       The following symbol is used in this and following sections to describe parsing behavior:

       escape    If a character is  referred  to  as  ``<backslash>-escaped''  or  ``<control>‐V-
                 escaped'',  it  shall mean that the character acquired or lost a special meaning
                 by virtue of being preceded,  respectively,  by  a  <backslash>  or  <control>‐V
                 character. Unless otherwise specified, the escaping character shall be discarded
                 at that time and shall not be further considered for any purpose.

       Command-line parsing shall be done in the  following  steps.  For  each  step,  characters
       already  evaluated  shall  be ignored; that is, the phrase ``leading character'' refers to
       the next character that has not yet been evaluated.

        1. Leading <colon> characters shall be skipped.

        2. Leading <blank> characters shall be skipped.

        3. If the leading character is  a  double-quote  character,  the  characters  up  to  and
           including  the  next  non-<backslash>-escaped  <newline>  shall  be discarded, and any
           subsequent characters shall be parsed as a separate command.

        4. Leading characters that can be  interpreted  as  addresses  shall  be  evaluated;  see
           Addressing in ex.

        5. Leading <blank> characters shall be skipped.

        6. If the next character is a <vertical-line> character or a <newline>:

            a. If the next character is a <newline>:

                i.  If  ex  is  in open or visual mode, the current line shall be set to the last
                    address specified, if any.

               ii.  Otherwise, if the last command was terminated by a <vertical-line> character,
                    no  action  shall  be  taken;  for  example,  the command "||<newline>" shall
                    execute two implied commands, not three.

               iii. Otherwise, step 6.b. shall apply.

            b. Otherwise, the implied command shall be the print command. The last #,  p,  and  l
               flags  specified  to  any  ex  command shall be remembered and shall apply to this
               implied command.  Executing the ex number, print, or list command  shall  set  the
               remembered  flags  to  #,  nothing,  and  l,  respectively,  plus  any other flags
               specified for that execution of the number, print, or list command.

               If ex is not currently performing a global or v command, and no address  or  count
               is  specified,  the  current  line shall be incremented by 1 before the command is
               executed. If incrementing the current line would result in  an  address  past  the
               last  line in the edit buffer, the command shall fail, and the increment shall not
               happen.

            c. The <newline> or <vertical-line> character shall be discarded and  any  subsequent
               characters shall be parsed as a separate command.

        7. The  command  name  shall  be comprised of the next character (if the character is not
           alphabetic), or the next character and any subsequent alphabetic  characters  (if  the
           character is alphabetic), with the following exceptions:

            a. Commands  that consist of any prefix of the characters in the command name delete,
               followed immediately by any of the characters 'l', 'p', '+', '-', or '#' shall  be
               interpreted as a delete command, followed by a <blank>, followed by the characters
               that were not part of the prefix of the delete  command.  The  maximum  number  of
               characters  shall  be matched to the command name delete; for example, "del" shall
               not be treated as "de" followed by the flag l.

            b. Commands that consist of the character 'k', followed by a character  that  can  be
               used  as the name of a mark, shall be equivalent to the mark command followed by a
               <blank>, followed by the character that followed the 'k'.

            c. Commands that consist of the character 's', followed by characters that  could  be
               interpreted  as  valid  options to the s command, shall be the equivalent of the s
               command, without any  pattern  or  replacement  values,  followed  by  a  <blank>,
               followed by the characters after the 's'.

        8. The  command  name  shall be matched against the possible command names, and a command
           name that contains a prefix matching the characters specified by the user shall be the
           executed  command.  In the case of commands where the characters specified by the user
           could be ambiguous, the executed command shall be as follows:

                                  ┌───┬────────┬┬───┬───────┬┬───┬───────┐
                                  │aappend ││nnext  ││tt     │
                                  │cchange ││pprint ││uundo  │
                                  │chchange ││prprint ││unundo  │
                                  │eedit   ││rread  ││vv     │
                                  │mmove   ││reread  ││wwrite │
                                  │mamark   ││ss     ││   │       │
                                  └───┴────────┴┴───┴───────┴┴───┴───────┘
           Implementation extensions with names causing similar ambiguities shall not be  checked
           for  a  match  until  all possible matches for commands specified by POSIX.1‐2008 have
           been checked.

        9. If the command is a !  command, or if the command is a read command followed  by  zero
           or  more  <blank> characters and a !, or if the command is a write command followed by
           one or more <blank> characters and a !, the rest of  the  command  shall  include  all
           characters  up  to  a  non-<backslash>-escaped  <newline>.   The  <newline>  shall  be
           discarded and any subsequent characters shall be parsed as a separate ex command.

       10. Otherwise, if the command is an edit, ex, or next command, or a visual  command  while
           in open or visual mode, the next part of the command shall be parsed as follows:

            a. Any  '!'  character immediately following the command shall be skipped and be part
               of the command.

            b. Any leading <blank> characters shall be skipped and be part of the command.

            c. If the next character is a '+', characters up to the first non-<backslash>-escaped
               <newline>  or  non-<backslash>-escaped <blank> shall be skipped and be part of the
               command.

            d. The rest of the command shall be determined by the steps  specified  in  paragraph
               12.

       11. Otherwise,  if  the  command  is a global, open, s, or v command, the next part of the
           command shall be parsed as follows:

            a. Any leading <blank> characters shall be skipped and be part of the command.

            b. If  the  next  character  is  not  an   alphanumeric,   double-quote,   <newline>,
               <backslash>, or <vertical-line> character:

                i.  The next character shall be used as a command delimiter.

               ii.  If  the  command  is a global, open, or v command, characters up to the first
                    non-<backslash>-escaped <newline>, or first non-<backslash>-escaped delimiter
                    character, shall be skipped and be part of the command.

               iii. If   the   command   is   an   s   command,   characters   up  to  the  first
                    non-<backslash>-escaped   <newline>,   or   second    non-<backslash>-escaped
                    delimiter character, shall be skipped and be part of the command.

            c. If   the   command  is  a  global  or  v  command,  characters  up  to  the  first
               non-<backslash>-escaped <newline> shall be skipped and be part of the command.

            d. Otherwise, the rest of the command shall be determined by the steps  specified  in
               paragraph 12.

       12. Otherwise:

            a. If  the  command was a map, unmap, abbreviate, or unabbreviate command, characters
               up to the first non-<control>‐V-escaped  <newline>,  <vertical-line>,  or  double-
               quote character shall be skipped and be part of the command.

            b. Otherwise,   characters   up   to  the  first  non-<backslash>-escaped  <newline>,
               <vertical-line>, or double-quote character shall be skipped and  be  part  of  the
               command.

            c. If  the command was an append, change, or insert command, and the step 12.b. ended
               at a  <vertical-line>  character,  any  subsequent  characters,  up  to  the  next
               non-<backslash>-escaped <newline> shall be used as input text to the command.

            d. If  the  command was ended by a double-quote character, all subsequent characters,
               up to the next non-<backslash>-escaped <newline>, shall be discarded.

            e. The terminating <newline> or <vertical-line> character shall be discarded and  any
               subsequent characters shall be parsed as a separate ex command.

       Command  arguments  shall  be  parsed as described by the Synopsis and Description of each
       individual ex command. This parsing shall not  be  <blank>-sensitive,  except  for  the  !
       argument,  which  must follow the command name without intervening <blank> characters, and
       where it would otherwise be ambiguous. For example, count and flag arguments need  not  be
       <blank>-separated  because  "d22p"  is  not  ambiguous,  but file arguments to the ex next
       command must be separated by one or  more  <blank>  characters.  Any  <blank>  in  command
       arguments  for  the  abbreviate, unabbreviate, map, and unmap commands can be <control>‐V-
       escaped, in which case the <blank> shall not be used as an argument delimiter. Any <blank>
       in  the  command  argument for any other command can be <backslash>-escaped, in which case
       that <blank> shall not be used as an argument delimiter.

       Within command arguments for the abbreviate, unabbreviate, map, and  unmap  commands,  any
       character  can  be  <control>‐V-escaped.   All  such  escaped  characters shall be treated
       literally and shall have no special meaning. Within command arguments  for  all  other  ex
       commands that are not regular expressions or replacement strings, any character that would
       otherwise have a special meaning can be <backslash>-escaped.  Escaped characters shall  be
       treated  literally, without special meaning as shell expansion characters or '!', '%', and
       '#' expansion characters. See Regular Expressions in ex and Replacement Strings in ex  for
       descriptions of command arguments that are regular expressions or replacement strings.

       Non-<backslash>-escaped '%' characters appearing in file arguments to any ex command shall
       be replaced by the current pathname; unescaped '#' characters shall  be  replaced  by  the
       alternate  pathname.  It shall be an error if '%' or '#' characters appear unescaped in an
       argument and their corresponding values are not set.

       Non-<backslash>-escaped '!'  characters in the arguments to either the ex  !   command  or
       the open and visual mode !  command, or in the arguments to the ex read command, where the
       first non-<blank> after the command name is a '!'  character, or in the arguments  to  the
       ex  write command where the command name is followed by one or more <blank> characters and
       the first non-<blank> after the command name is a '!'  character, shall be  replaced  with
       the  arguments  to  the  last of those three commands as they appeared after all unescaped
       '%', '#', and '!'  characters were replaced. It shall  be  an  error  if  '!'   characters
       appear  unescaped in one of these commands and there has been no previous execution of one
       of these commands.

       If an error occurs during the parsing or execution of an ex command:

        *  An informational message to this effect shall be written. Execution of the ex  command
           shall  stop,  and  the  cursor (for example, the current line and column) shall not be
           further modified.

        *  If the ex command resulted  from  a  map  expansion,  all  characters  from  that  map
           expansion shall be discarded, except as otherwise specified by the map command.

        *  Otherwise,  if  the  ex  command resulted from the processing of an EXINIT environment
           variable, a .exrc file, a :source command, a -c option, or a +command specified to  an
           ex  edit,  ex,  next,  or  visual  command, no further commands from the source of the
           commands shall be executed.

        *  Otherwise, if the ex command resulted from the execution of a buffer or a global or  v
           command,  no further commands caused by the execution of the buffer or the global or v
           command shall be executed.

        *  Otherwise, if the ex command was not terminated by a <newline>, all characters  up  to
           and including the next non-<backslash>-escaped <newline> shall be discarded.

   Input Editing in ex
       The  following  symbol  is  used  in  this  and  the following sections to specify command
       actions:

       word      In the POSIX locale, a word consists of a maximal sequence of  letters,  digits,
                 and  underscores,  delimited  at  both  ends  by  characters other than letters,
                 digits, or underscores, or by the beginning or end of a line or the edit buffer.

       When accepting input characters from the user, in either ex command mode or ex text  input
       mode, ex shall enable canonical mode input processing, as defined in the System Interfaces
       volume of POSIX.1‐2017.

       If in ex text input mode:

        1. If the number edit option is set, ex shall prompt for input using the line number that
           would  be  assigned  to  the line if it is entered, in the format specified for the ex
           number command.

        2. If the autoindent edit option is set, ex  shall  prompt  for  input  using  autoindent
           characters,  as  described by the autoindent edit option.  autoindent characters shall
           follow the line number, if any.

       If in ex command mode:

        1. If the prompt edit option is set, input shall be  prompted  for  using  a  single  ':'
           character; otherwise, there shall be no prompt.

       The  input  characters  in  the following sections shall have the following effects on the
       input line.

   Scroll
       Synopsis:

                     eof

       See the description of the stty eof character in stty.

       If in ex command mode:

              If the eof character is the first character entered on the line, the line shall  be
              evaluated as if it contained two characters: a <control>‐D and a <newline>.

              Otherwise, the eof character shall have no special meaning.

       If in ex text input mode:

              If  the  cursor  follows  an autoindent character, the autoindent characters in the
              line shall be modified so that a part of the next  text  input  character  will  be
              displayed on the first column in the line after the previous shiftwidth edit option
              column boundary, and the user shall be prompted again for input for the same line.

              Otherwise, if the cursor follows a '0', which follows an autoindent character,  and
              the  '0'  was  the  previous  text  input  character,  the  '0'  and all autoindent
              characters in the line shall be discarded, and the user shall be prompted again for
              input for the same line.

              Otherwise,  if the cursor follows a '^', which follows an autoindent character, and
              the '^' was  the  previous  text  input  character,  the  '^'  and  all  autoindent
              characters in the line shall be discarded, and the user shall be prompted again for
              input for the same line. In addition, the autoindent level for the next input  line
              shall be derived from the same line from which the autoindent level for the current
              input line was derived.

              Otherwise, if there are no autoindent or text input characters in the line, the eof
              character shall be discarded.

              Otherwise, the eof character shall have no special meaning.

   <newline>
       Synopsis:

                     <newline>
                     <control>-J

       If in ex command mode:

              Cause  the  command line to be parsed; <control>‐J shall be mapped to the <newline>
              for this purpose.

       If in ex text input mode:

              Terminate the current line. If  there  are  no  characters  other  than  autoindent
              characters on the line, all characters on the line shall be discarded.

              Prompt  for text input on a new line after the current line. If the autoindent edit
              option is set, an appropriate number of autoindent characters shall be added  as  a
              prefix to the line as described by the ex autoindent edit option.

   <backslash>
       Synopsis:

                     <backslash>

       Allow  the entry of a subsequent <newline> or <control>‐J as a literal character, removing
       any special meaning that it may have to the editor during text input mode. The <backslash>
       character shall be retained and evaluated when the command line is parsed, or retained and
       included when the input text becomes part of the edit buffer.

   <control>‐V
       Synopsis:

                     <control>-V

       Allow the entry of any subsequent character as a literal character, removing  any  special
       meaning  that  it may have to the editor during text input mode. The <control>‐V character
       shall be discarded before the command line is parsed or the input text becomes part of the
       edit buffer.

       If  the  ``literal  next''  functionality  is  performed  by  the underlying system, it is
       implementation-defined whether a character other than <control>‐V performs this function.

   <control>‐W
       Synopsis:

                     <control>-W

       Discard the <control>‐W, and the word previous to it in  the  input  line,  including  any
       <blank>  characters  following  the  word  and  preceding  the <control>‐W.  If the ``word
       erase'' functionality is performed by the underlying system, it is  implementation-defined
       whether a character other than <control>‐W performs this function.

   Command Descriptions in ex
       The  following  symbols  are  used in this section to represent command modifiers. Some of
       these modifiers can be omitted, in which case the specified defaults shall be used.

       1addr     A single line address, given in any of the forms described in Addressing in  ex;
                 the default shall be the current line ('.'), unless otherwise specified.

                 If the line address is zero, it shall be an error, unless otherwise specified in
                 the following command descriptions.

                 If the edit buffer is empty, and the address is specified with a  command  other
                 than  =, append, insert, open, put, read, or visual, or the address is not zero,
                 it shall be an error.

       2addr     Two addresses specifying an inclusive  range  of  lines.  If  no  addresses  are
                 specified,  the default for 2addr shall be the current line only (".,."), unless
                 otherwise specified in the following command descriptions.  If  one  address  is
                 specified, 2addr shall specify that line only, unless otherwise specified in the
                 following command descriptions.

                 It shall be an error if the first address is greater than the second address.

                 If the edit buffer is empty, and the two addresses are specified with a  command
                 other  than the !, write, wq, or xit commands, or either address is not zero, it
                 shall be an error.

       count     A positive decimal number. If count is specified,  it  shall  be  equivalent  to
                 specifying  an  additional address to the command, unless otherwise specified by
                 the following command descriptions. The additional address shall be equal to the
                 last  address  specified  to  the command (either explicitly or by default) plus
                 count-1.

                 If this would result in an address greater  than  the  last  line  of  the  edit
                 buffer, it shall be corrected to equal the last line of the edit buffer.

       flags     One  or  more  of  the  characters  '+',  '-',  '#', 'p', or 'l' (ell). The flag
                 characters can be <blank>-separated,  and  in  any  order  or  combination.  The
                 characters  '#',  'p',  and  'l'  shall  cause lines to be written in the format
                 specified by the print command with the specified flags.

                 The lines to be written are as follows:

                  1. All edit buffer lines written during the execution of the  ex  &,  ~,  list,
                     number, open, print, s, visual, and z commands shall be written as specified
                     by flags.

                  2. After the completion of an ex command  with  a  flag  as  an  argument,  the
                     current line shall be written as specified by flags, unless the current line
                     was the last line written by the command.

                 The characters '+' and '-' cause  the  value  of  the  current  line  after  the
                 execution of the ex command to be adjusted by the offset address as described in
                 Addressing in ex.  This adjustment  shall  occur  before  the  current  line  is
                 written as described in 2. above.

                 The default for flags shall be none.

       buffer    One of a number of named areas for holding text. The named buffers are specified
                 by the alphanumeric characters of the POSIX locale.  There  shall  also  be  one
                 ``unnamed''  buffer.  When no buffer is specified for editor commands that use a
                 buffer, the unnamed buffer shall be used.  Commands that store text into buffers
                 shall  store  the text as it was before the command took effect, and shall store
                 text occurring earlier in the file before text  occurring  later  in  the  file,
                 regardless  of  how the text region was specified. Commands that store text into
                 buffers shall store the text into the unnamed buffer as well  as  any  specified
                 buffer.

                 In  ex  commands,  buffer  names are specified as the name by itself. In open or
                 visual mode commands the name is preceded by a double-quote ('"') character.

                 If the specified buffer name is an uppercase character, and the buffer  contents
                 are  to  be  modified,  the  buffer  shall  be  appended  to  rather  than being
                 overwritten. If the buffer is not being modified, specifying the buffer name  in
                 lowercase and uppercase shall have identical results.

                 There shall also be buffers named by the numbers 1 through 9. In open and visual
                 mode, if a region of text including characters from more than a single  line  is
                 being  modified  by the vi c or d commands, the motion character associated with
                 the c or d commands specifies that the buffer text shall be in line mode, or the
                 commands %, `, /, ?, (, ), N, n, {, or } are used to define a region of text for
                 the c or d commands, the contents of buffers 1 through 8 shall be moved into the
                 buffer  named  by  the  next numerically greater value, the contents of buffer 9
                 shall be discarded, and the region of text shall be copied into buffer  1.  This
                 shall be in addition to copying the text into a user-specified buffer or unnamed
                 buffer, or both. Numeric buffers can be specified as a source  buffer  for  open
                 and  visual  mode  commands;  however,  specifying a numeric buffer as the write
                 target of an open or visual mode command shall have unspecified results.

                 The text of each buffer shall have the characteristic of being in either line or
                 character mode. Appending text to a non-empty buffer shall set the mode to match
                 the characteristic of the text being appended. Appending text to a buffer  shall
                 cause  the  creation  of  at  least  one additional line in the buffer. All text
                 stored into buffers by ex commands shall be in line mode. The ex  commands  that
                 use  buffers as the source of text specify individually how buffers of different
                 modes are handled. Each open or visual mode command that uses  buffers  for  any
                 purpose  specifies  individually the mode of the text stored into the buffer and
                 how buffers of different modes are handled.

       file      Command text used to derive  a  pathname.  The  default  shall  be  the  current
                 pathname,  as  defined previously, in which case, if no current pathname has yet
                 been established it shall be an error, except where specifically  noted  in  the
                 individual  command  descriptions that follow.  If the command text contains any
                 of the characters '~', '{', '[', '*', '?', '$',  '"',  backquote,  single-quote,
                 and  <backslash>,  it shall be subjected to the process of ``shell expansions'',
                 as described below; if more than a  single  pathname  results  and  the  command
                 expects only one, it shall be an error.

                 The  process  of shell expansions in the editor shall be done as follows. The ex
                 utility shall pass two arguments to the program named by the shell edit  option;
                 the first shall be -c, and the second shall be the string "echo" and the command
                 text as a single argument. The  standard  output  and  standard  error  of  that
                 command shall replace the command text.

       !         A character that can be appended to the command name to modify its operation, as
                 detailed in the individual command descriptions. With the exception  of  the  ex
                 read, write, and !  commands, the '!'  character shall only act as a modifier if
                 there are no <blank> characters between it and the command name.

       remembered search direction
                 The vi commands N and n begin searching in a forwards or backwards direction  in
                 the  edit  buffer  based  on  a  remembered search direction, which is initially
                 unset, and is set by the ex global, v, s, and tag commands, and the vi /  and  ?
                 commands.

   Abbreviate
       Synopsis:

                     ab[breviate][lhs rhs]

       If  lhs  and rhs are not specified, write the current list of abbreviations and do nothing
       more.

       Implementations may restrict the set of characters accepted in lhs  or  rhs,  except  that
       printable   characters   and  <blank>  characters  shall  not  be  restricted.  Additional
       restrictions shall be implementation-defined.

       In both lhs and rhs, any character may be escaped with a <control>‐V, in  which  case  the
       character shall not be used to delimit lhs from rhs, and the escaping <control>‐V shall be
       discarded.

       In open and visual text input mode, if a non-word or <ESC> character that is  not  escaped
       by  a <control>‐V character is entered after a word character, a check shall be made for a
       set of characters matching lhs, in the text input entered during this command.  If  it  is
       found, the effect shall be as if rhs was entered instead of lhs.

       The set of characters that are checked is defined as follows:

        1. If  there  are no characters inserted before the word and non-word or <ESC> characters
           that triggered the check, the set of characters shall consist of the word character.

        2. If the character inserted before the  word  and  non-word  or  <ESC>  characters  that
           triggered  the  check  is a word character, the set of characters shall consist of the
           characters inserted  immediately  before  the  triggering  characters  that  are  word
           characters, plus the triggering word character.

        3. If  the  character  inserted  before  the  word  and non-word or <ESC> characters that
           triggered the check is not a word character, the set of characters  shall  consist  of
           the  characters  that  were inserted before the triggering characters that are neither
           <blank> characters nor word characters, plus the triggering word character.

       It is unspecified whether the lhs argument entered for the ex abbreviate and  unabbreviate
       commands is replaced in this fashion. Regardless of whether or not the replacement occurs,
       the effect of the command shall be as if the replacement had not occurred.

       Current line: Unchanged.

       Current column: Unchanged.

   Append
       Synopsis:

                     [1addr] a[ppend][!]

       Enter ex text input mode; the input text shall be placed after the specified line. If line
       zero is specified, the text shall be placed at the beginning of the edit buffer.

       This  command  shall  be affected by the number and autoindent edit options; following the
       command name with '!'  shall cause the autoindent edit option setting to  be  toggled  for
       the duration of this command only.

       Current  line:  Set  to  the last input line; if no lines were input, set to the specified
       line, or to the first line of the edit buffer if a line of zero was specified, or zero  if
       the edit buffer is empty.

       Current column: Set to non-<blank>.

   Arguments
       Synopsis:

                     ar[gs]

       Write the current argument list, with the current argument-list entry, if any, between '['
       and ']' characters.

       Current line: Unchanged.

       Current column: Unchanged.

   Change
       Synopsis:

                     [2addr] c[hange][!][count]

       Enter ex text input mode; the input text shall replace the specified lines. The  specified
       lines shall be copied into the unnamed buffer, which shall become a line mode buffer.

       This  command  shall  be affected by the number and autoindent edit options; following the
       command name with '!'  shall cause the autoindent edit option setting to  be  toggled  for
       the duration of this command only.

       Current  line:  Set to the last input line; if no lines were input, set to the line before
       the first address, or to the first line of the edit buffer if there are no lines preceding
       the first address, or to zero if the edit buffer is empty.

       Current column: Set to non-<blank>.

   Change Directory
       Synopsis:

                     chd[ir][!][directory]
                     cd[!][directory]

       Change the current working directory to directory.

       If  no directory argument is specified, and the HOME environment variable is set to a non-
       null and non-empty value,  directory  shall  default  to  the  value  named  in  the  HOME
       environment  variable.  If  the  HOME  environment  variable is empty or is undefined, the
       default value of directory is implementation-defined.

       If no '!'  is appended to the command name, and the edit buffer has  been  modified  since
       the  last  complete write, and the current pathname does not begin with a '/', it shall be
       an error.

       Current line: Unchanged.

       Current column: Unchanged.

   Copy
       Synopsis:

                     [2addr] co[py] 1addr [flags]
                     [2addr] t 1addr [flags]

       Copy the specified lines after the specified destination line; line  zero  specifies  that
       the lines shall be placed at the beginning of the edit buffer.

       Current line: Set to the last line copied.

       Current column: Set to non-<blank>.

   Delete
       Synopsis:

                     [2addr] d[elete][buffer][count][flags]

       Delete  the  specified lines into a buffer (defaulting to the unnamed buffer), which shall
       become a line-mode buffer.

       Flags can immediately follow the command name; see Command Line Parsing in ex.

       Current line: Set to the line following the deleted lines, or to the last line in the edit
       buffer  if  that line is past the end of the edit buffer, or to zero if the edit buffer is
       empty.

       Current column: Set to non-<blank>.

   Edit
       Synopsis:

                     e[dit][!][+command][file]
                     ex[!][+command][file]

       If no '!'  is appended to the command name, and the edit buffer has  been  modified  since
       the last complete write, it shall be an error.

       If  file  is  specified,  replace the current contents of the edit buffer with the current
       contents of file, and set the current pathname to file.  If file is not specified, replace
       the current contents of the edit buffer with the current contents of the file named by the
       current pathname. If for any reason the current contents of the file cannot  be  accessed,
       the edit buffer shall be empty.

       The +command option shall be <blank>-delimited; <blank> characters within the +command can
       be escaped by  preceding  them  with  a  <backslash>  character.  The  +command  shall  be
       interpreted  as  an ex command immediately after the contents of the edit buffer have been
       replaced and the current line and column have been set.

       If the edit buffer is empty:

       Current line: Set to 0.

       Current column: Set to 1.

       Otherwise, if executed while in ex command mode or if the +command argument is specified:

       Current line: Set to the last line of the edit buffer.

       Current column: Set to non-<blank>.

       Otherwise, if file is omitted or results in the current pathname:

       Current line: Set to the first line of the edit buffer.

       Current column: Set to non-<blank>.

       Otherwise, if file is the same as the last file edited, the line and column shall  be  set
       as follows; if the file was previously edited, the line and column may be set as follows:

       Current  line: Set to the last value held when that file was last edited. If this value is
       not a valid line in the new edit buffer, set to the first line of the edit buffer.

       Current column: If the current line was set to the last value held when the file was  last
       edited,  set  to  the last value held when the file was last edited.  Otherwise, or if the
       last value is not a valid column in the new edit buffer, set to non-<blank>.

       Otherwise:

       Current line: Set to the first line of the edit buffer.

       Current column: Set to non-<blank>.

   File
       Synopsis:

                     f[ile][file]

       If a file argument is specified, the alternate  pathname  shall  be  set  to  the  current
       pathname, and the current pathname shall be set to file.

       Write  an  informational message. If the file has a current pathname, it shall be included
       in this message; otherwise, the message shall indicate that there is no current  pathname.
       If  the edit buffer contains lines, the current line number and the number of lines in the
       edit buffer shall be included in this message; otherwise, the message shall indicate  that
       the  edit  buffer  is  empty. If the edit buffer has been modified since the last complete
       write, this fact shall be included in this message. If the readonly edit  option  is  set,
       this  fact  shall  be  included in this message. The message may contain other unspecified
       information.

       Current line: Unchanged.

       Current column: Unchanged.

   Global
       Synopsis:

                     [2addr] g[lobal] /pattern/ [commands]
                     [2addr] v /pattern/ [commands]

       The optional '!'  character after the global command shall be the same as executing the  v
       command.

       If pattern is empty (for example, "//") or not specified, the last regular expression used
       in the editor command shall be used as the pattern.   The  pattern  can  be  delimited  by
       <slash> characters (shown in the Synopsis), as well as any non-alphanumeric or non-<blank>
       other than <backslash>, <vertical-line>, <newline>, or double-quote.

       If no lines are specified, the lines shall default to the entire file.

       The global and v commands are logically two-pass operations. First, mark the lines  within
       the  specified  lines  for  which  the  line  excluding  the terminating <newline> matches
       (global) or does not match (v or global!)  the specified pattern. Second, execute  the  ex
       commands  given  by  commands, with the current line ('.')  set to each marked line. If an
       error occurs during this process, or the contents of the edit  buffer  are  replaced  (for
       example,  by  the ex :edit command) an error message shall be written and no more commands
       resulting from the execution of this command shall be processed.

       Multiple ex commands can be specified by entering multiple commands on a single line using
       a  <vertical-line>  to  delimit  them,  or one per line, by escaping each <newline> with a
       <backslash>.

       If no commands are specified:

        1. If in ex command mode, it shall be as if the print command were specified.

        2. Otherwise, no command shall be executed.

       For the append, change, and insert commands, the input text shall be included as  part  of
       the  command,  and the terminating <period> can be omitted if the command ends the list of
       commands. The open and visual commands can be specified as one of the commands,  in  which
       case  each  marked  line  shall  cause the editor to enter open or visual mode. If open or
       visual mode is exited using the vi Q command, the current line shall be set  to  the  next
       marked  line,  and  open  or  visual  mode  reentered,  until  the list of marked lines is
       exhausted.

       The global, v, and undo commands cannot be used in commands.  Marked lines may be  deleted
       by  commands  executed  for  lines occurring earlier in the file than the marked lines. In
       this case, no commands shall be executed for the deleted lines.

       If the remembered search direction is not set, the global and v commands shall set  it  to
       forward.

       The  autoprint and autoindent edit options shall be inhibited for the duration of the g or
       v command.

       Current line: If no commands  executed,  set  to  the  last  marked  line.  Otherwise,  as
       specified for the executed ex commands.

       Current  column:  If no commands are executed, set to non-<blank>; otherwise, as specified
       for the individual ex commands.

   Insert
       Synopsis:

                     [1addr] i[nsert][!]

       Enter ex text input mode; the input text shall be placed before the specified line. If the
       line is zero or 1, the text shall be placed at the beginning of the edit buffer.

       This  command  shall  be affected by the number and autoindent edit options; following the
       command name with '!'  shall cause the autoindent edit option setting to  be  toggled  for
       the duration of this command only.

       Current  line:  Set to the last input line; if no lines were input, set to the line before
       the specified line, or to the first line  of  the  edit  buffer  if  there  are  no  lines
       preceding the specified line, or zero if the edit buffer is empty.

       Current column: Set to non-<blank>.

   Join
       Synopsis:

                     [2addr] j[oin][!][count][flags]

       If count is specified:

              If  no  address  was  specified, the join command shall behave as if 2addr were the
              current line and the current line plus count (.,. + count).

              If one address was specified, the join command shall behave as if  2addr  were  the
              specified address and the specified address plus count (addr,addr + count).

              If  two addresses were specified, the join command shall behave as if an additional
              address, equal to the last address plus count -1 (addr1,addr2,addr2  +  count  -1),
              was specified.

              If  this  would  result  in a second address greater than the last line of the edit
              buffer, it shall be corrected to be equal to the last line of the edit buffer.

       If no count is specified:

              If no address was specified, the join command shall behave as  if  2addr  were  the
              current line and the next line (.,. +1).

              If  one  address  was specified, the join command shall behave as if 2addr were the
              specified address and the next line (addr,addr +1).

       Join the text from the specified lines together into a single line,  which  shall  replace
       the specified lines.

       If  a  '!'   character  is  appended  to  the  command  name,  the  join  shall be without
       modification of any line, independent of the current locale.

       Otherwise, in the POSIX locale, set the current line to the first of the specified  lines,
       and then, for each subsequent line, proceed as follows:

        1. Discard leading <space> characters from the line to be joined.

        2. If the line to be joined is now empty, delete it, and skip steps 3 through 5.

        3. If the current line ends in a <blank>, or the first character of the line to be joined
           is a ')' character, join the lines without further modification.

        4. If the last character of the current line is a '.', join the lines  with  two  <space>
           characters between them.

        5. Otherwise, join the lines with a single <space> between them.

       Current line: Set to the first line specified.

       Current column: Set to non-<blank>.

   List
       Synopsis:

                     [2addr] l[ist][count][flags]

       This command shall be equivalent to the ex command:

           [2addr] p[rint][count] l[flags]

       See Print.

   Map
       Synopsis:

                     map[!][lhs rhs]

       If lhs and rhs are not specified:

        1. If '!'  is specified, write the current list of text input mode maps.

        2. Otherwise, write the current list of command mode maps.

        3. Do nothing more.

       Implementations  may  restrict  the  set of characters accepted in lhs or rhs, except that
       printable  characters  and  <blank>  characters  shall  not  be   restricted.   Additional
       restrictions  shall  be  implementation-defined. In both lhs and rhs, any character can be
       escaped with a <control>‐V, in which case the character shall not be used to  delimit  lhs
       from rhs, and the escaping <control>‐V shall be discarded.

       If  the character '!'  is appended to the map command name, the mapping shall be effective
       during open or visual text input mode rather than open or visual command mode. This allows
       lhs  to  have two different map definitions at the same time: one for command mode and one
       for text input mode.

       For command mode mappings:

              When the lhs is entered as any part of a vi command in open or visual mode (but not
              as  part  of  the  arguments  to  the  command),  the  action  shall  be  as if the
              corresponding rhs had been entered.

              If any character in  the  command,  other  than  the  first,  is  escaped  using  a
              <control>‐V character, that character shall not be part of a match to an lhs.

              It  is unspecified whether implementations shall support map commands where the lhs
              is more than a single character in length, where the first character of the lhs  is
              printable.

              If lhs contains more than one character and the first character is '#', followed by
              a sequence of digits corresponding to a  numbered  function  key,  then  when  this
              function  key  is  typed  it  shall be mapped to rhs.  Characters other than digits
              following a '#' character also represent the function key named by  the  characters
              in  the  lhs  following  the  '#'  and may be mapped to rhs.  It is unspecified how
              function keys are named or what function keys are supported.

       For text input mode mappings:

              When the lhs is entered as any part of text entered in open or  visual  text  input
              modes, the action shall be as if the corresponding rhs had been entered.

              If  any  character in the input text is escaped using a <control>‐V character, that
              character shall not be part of a match to an lhs.

              It is unspecified whether the lhs text entered for subsequent map or unmap commands
              is replaced with the rhs text for the purposes of the screen display; regardless of
              whether or not the display appears as if the corresponding rhs  text  was  entered,
              the effect of the command shall be as if the lhs text was entered.

       If  only  part  of the lhs is entered, it is unspecified how long the editor will wait for
       additional, possibly matching characters before treating the already entered characters as
       not matching the lhs.

       The rhs characters shall themselves be subject to remapping, unless otherwise specified by
       the remap edit option, except that if the characters in lhs occur as prefix characters  in
       rhs, those characters shall not be remapped.

       On block-mode terminals, the mapping need not occur immediately (for example, it may occur
       after the terminal transmits a group of characters to the system), but  it  shall  achieve
       the same results as if it occurred immediately.

       Current line: Unchanged.

       Current column: Unchanged.

   Mark
       Synopsis:

                     [1addr] ma[rk] character
                     [1addr] k character

       Implementations  shall  support character values of a single lowercase letter of the POSIX
       locale and the backquote and single-quote  characters;  support  of  other  characters  is
       implementation-defined.

       If  executing  the  vi  m  command, set the specified mark to the current line and 1-based
       numbered character referenced by the current column, if any; otherwise, column position 1.

       Otherwise, set the specified mark  to  the  specified  line  and  1-based  numbered  first
       non-<blank>  non-<newline>  in  the line, if any; otherwise, the last non-<newline> in the
       line, if any; otherwise, column position 1.

       The mark shall remain associated with the line until the mark is  reset  or  the  line  is
       deleted.  If a deleted line is restored by a subsequent undo command, any marks previously
       associated with the line, which have not been reset, shall be restored as well. Any use of
       a mark not associated with a current line in the edit buffer shall be an error.

       The  marks  ` and ' shall be set as described previously, immediately before the following
       events occur in the editor:

        1. The use of '$' as an ex address

        2. The use of a positive decimal number as an ex address

        3. The use of a search command as an ex address

        4. The use of a mark reference as an ex address

        5. The use of the following open and visual mode commands: <control>‐], %, (, ), [, ], {,
           }

        6. The  use  of  the  following  open  and  visual mode commands: ', G, H, L, M, z if the
           current line will change as a result of the command

        7. The use of the open and visual mode commands: /, ?, N, `, n if  the  current  line  or
           column will change as a result of the command

        8. The use of the ex mode commands: z, undo, global, v

       For  rules  1.,  2.,  3.,  and 4., the ` and ' marks shall not be set if the ex command is
       parsed as specified by rule 6.a. in Command Line Parsing in ex.

       For rules 5., 6., and 7., the ` and ' marks shall not be set if the commands are  used  as
       motion commands in open and visual mode.

       For  rules  1.,  2., 3., 4., 5., 6., 7., and 8., the ` and ' marks shall not be set if the
       command fails.

       The ` and ' marks shall be set as described previously, each time the contents of the edit
       buffer  are  replaced  (including the editing of the initial buffer), if in open or visual
       mode, or if in ex mode and the edit buffer is not empty, before any commands or  movements
       (including  commands  or  movements  specified  by  the  -c  or -t options or the +command
       argument) are executed on the edit buffer. If in open or visual mode, the marks  shall  be
       set as if executing the vi m command; otherwise, as if executing the ex mark command.

       When  changing  from  ex mode to open or visual mode, if the ` and ' marks are not already
       set, the ` and ' marks shall be set as described previously.

       Current line: Unchanged.

       Current column: Unchanged.

   Move
       Synopsis:

                     [2addr] m[ove] 1addr [flags]

       Move the specified lines after the specified destination line. A destination of line  zero
       specifies  that the lines shall be placed at the beginning of the edit buffer. It shall be
       an error if the destination line is within the range of lines to be moved.

       Current line: Set to the last of the moved lines.

       Current column: Set to non-<blank>.

   Next
       Synopsis:

                     n[ext][!][+command][file ...]

       If no '!'  is appended to the command name, and the edit buffer has  been  modified  since
       the  last complete write, it shall be an error, unless the file is successfully written as
       specified by the autowrite option.

       If one or more files is specified:

        1. Set the argument list to the specified filenames.

        2. Set the current argument list reference to be the first entry in the argument list.

        3. Set the current pathname to the first filename specified.

       Otherwise:

        1. It shall be an error if there are no more filenames in the  argument  list  after  the
           filename currently referenced.

        2. Set the current pathname and the current argument list reference to the filename after
           the filename currently referenced in the argument list.

       Replace the contents of the edit buffer with the contents of the file named by the current
       pathname.  If  for any reason the contents of the file cannot be accessed, the edit buffer
       shall be empty.

       This command shall be affected by the autowrite and writeany edit options.

       The +command option shall be <blank>-delimited;  <blank>  characters  can  be  escaped  by
       preceding  them  with  a <backslash> character. The +command shall be interpreted as an ex
       command immediately after the contents of the edit  buffer  have  been  replaced  and  the
       current line and column have been set.

       Current line: Set as described for the edit command.

       Current column: Set as described for the edit command.

   Number
       Synopsis:

                     [2addr] nu[mber][count][flags]
                     [2addr] #[count][flags]

       These commands shall be equivalent to the ex command:

           [2addr] p[rint][count] #[flags]

       See Print.

   Open
       Synopsis:

                     [1addr] o[pen] /pattern/ [flags]

       This  command need not be supported on block-mode terminals or terminals with insufficient
       capabilities. If standard input, standard output,  or  standard  error  are  not  terminal
       devices, the results are unspecified.

       Enter open mode.

       The  trailing  delimiter  can  be  omitted from pattern at the end of the command line. If
       pattern is empty (for example, "//") or not specified, the last regular expression used in
       the  editor  shall  be  used  as  the  pattern.  The  pattern  can be delimited by <slash>
       characters (shown in the Synopsis), as well as any alphanumeric, or non-<blank> other than
       <backslash>, <vertical-line>, <newline>, or double-quote.

       Current line: Set to the specified line.

       Current column: Set to non-<blank>.

   Preserve
       Synopsis:

                     pre[serve]

       Save  the  edit  buffer in a form that can later be recovered by using the -r option or by
       using the ex recover command. After the file has been preserved, a mail message  shall  be
       sent  to  the  user.  This  message  shall  be readable by invoking the mailx utility. The
       message shall contain the name of the file, the time of preservation, and  an  ex  command
       that could be used to recover the file. Additional information may be included in the mail
       message.

       Current line: Unchanged.

       Current column: Unchanged.

   Print
       Synopsis:

                     [2addr] p[rint][count][flags]

       Write the addressed lines. The behavior is unspecified if the number  of  columns  on  the
       display  is  less than the number of columns required to write any single character in the
       lines being written.

       Non-printable characters, except for the <tab>, shall be written as implementation-defined
       multi-character sequences.

       If  the  # flag is specified or the number edit option is set, each line shall be preceded
       by its line number in the following format:

           "%6d  ", <line number>

       If the l flag is specified or the list edit option is set:

        1. The characters listed in the Base  Definitions  volume  of  POSIX.1‐2017,  Table  5-1,
           Escape  Sequences  and Associated Actions shall be written as the corresponding escape
           sequence.

        2. Non-printable characters not in the Base Definitions  volume  of  POSIX.1‐2017,  Table
           5-1, Escape Sequences and Associated Actions shall be written as one three-digit octal
           number (with a preceding <backslash>) for each byte in the character (most significant
           byte first).

        3. The end of each line shall be marked with a '$', and literal '$' characters within the
           line shall be written with a preceding <backslash>.

       Long lines shall be folded; the length at which folding occurs is unspecified, but  should
       be appropriate for the output terminal, considering the number of columns of the terminal.

       If  a line is folded, and the l flag is not specified and the list edit option is not set,
       it is unspecified whether a multi-column character at the folding position  is  separated;
       it shall not be discarded.

       Current line: Set to the last written line.

       Current column: Unchanged if the current line is unchanged; otherwise, set to non-<blank>.

   Put
       Synopsis:

                     [1addr] pu[t][buffer]

       Append  text  from  the specified buffer (by default, the unnamed buffer) to the specified
       line; line zero specifies that the text shall be placed  at  the  beginning  of  the  edit
       buffer.  Each  portion of a line in the buffer shall become a new line in the edit buffer,
       regardless of the mode of the buffer.

       Current line: Set to the last line entered into the edit buffer.

       Current column: Set to non-<blank>.

   Quit
       Synopsis:

                     q[uit][!]

       If no '!'  is appended to the command name:

        1. If the edit buffer has been modified since the last complete write,  it  shall  be  an
           error.

        2. If  there  are filenames in the argument list after the filename currently referenced,
           and the last command was not a quit, wq, xit, or ZZ (see Exit) command, it shall be an
           error.

       Otherwise, terminate the editing session.

   Read
       Synopsis:

                     [1addr] r[ead][!][file]

       If  '!'   is not the first non-<blank> to follow the command name, a copy of the specified
       file shall be appended into the edit buffer after the specified line; line zero  specifies
       that the copy shall be placed at the beginning of the edit buffer. The number of lines and
       bytes read shall be written. If no file is  named,  the  current  pathname  shall  be  the
       default.  If there is no current pathname, then file shall become the current pathname. If
       there is no current pathname or file operand, it shall be an error. Specifying a file that
       is not of type regular shall have unspecified results.

       Otherwise, if file is preceded by '!', the rest of the line after the '!'  shall have '%',
       '#', and '!'  characters expanded as described in Command Line Parsing in ex.

       The ex utility shall then pass two arguments to  the  program  named  by  the  shell  edit
       option;  the  first shall be -c and the second shall be the expanded arguments to the read
       command as a single argument. The standard input of  the  program  shall  be  set  to  the
       standard  input  of  the  ex  program when it was invoked. The standard error and standard
       output of the program shall be appended into the edit buffer after the specified line.

       Each line in the copied file or program output (as delimited by  <newline>  characters  or
       the  end of the file or output if it is not immediately preceded by a <newline>), shall be
       a separate line in the edit buffer. Any occurrences  of  <carriage-return>  and  <newline>
       pairs in the output shall be treated as single <newline> characters.

       The  special  meaning of the '!'  following the read command can be overridden by escaping
       it with a <backslash> character.

       Current line: If no lines are added to the edit buffer, unchanged. Otherwise, if  in  open
       or  visual mode, set to the first line entered into the edit buffer. Otherwise, set to the
       last line entered into the edit buffer.

       Current column: Set to non-<blank>.

   Recover
       Synopsis:

                     rec[over][!] file

       If no '!'  is appended to the command name, and the edit buffer has  been  modified  since
       the last complete write, it shall be an error.

       If  no  file operand is specified, then the current pathname shall be used. If there is no
       current pathname or file operand, it shall be an error.

       If no recovery information has previously been saved about file, the recover command shall
       behave  identically to the edit command, and an informational message to this effect shall
       be written.

       Otherwise, set the current pathname to file, and replace the current contents of the  edit
       buffer  with  the recovered contents of file.  If there are multiple instances of the file
       to be recovered, the one most recently saved shall  be  recovered,  and  an  informational
       message  that  there  are  previous  versions  of  the file that can be recovered shall be
       written. The editor shall behave as if the contents of the edit buffer have  already  been
       modified.

       Current file: Set as described for the edit command.

       Current column: Set as described for the edit command.

   Rewind
       Synopsis:

                     rew[ind][!]

       If  no  '!'   is appended to the command name, and the edit buffer has been modified since
       the last complete write, it shall be an error, unless the file is successfully written  as
       specified by the autowrite option.

       If the argument list is empty, it shall be an error.

       The  current  argument  list  reference and the current pathname shall be set to the first
       filename in the argument list.

       Replace the contents of the edit buffer with the contents of the file named by the current
       pathname.  If  for any reason the contents of the file cannot be accessed, the edit buffer
       shall be empty.

       This command shall be affected by the autowrite and writeany edit options.

       Current line: Set as described for the edit command.

       Current column: Set as described for the edit command.

   Set
       Synopsis:

                     se[t][option[=[value]] ...][nooption ...][option? ...][all]

       When no arguments are specified, write the value of the term edit option and those options
       whose  values  have  been  changed  from  the  default  settings; when the argument all is
       specified, write all of the option values.

       Giving an option name followed by the character '?'  shall cause the current value of that
       option  to  be  written.  The  '?'   can be separated from the option name by zero or more
       <blank> characters. The '?'  shall be necessary only for Boolean valued  options.  Boolean
       options can be given values by the form set option to turn them on or set nooption to turn
       them off; string and numeric options can be assigned by the form  set  option=value.   Any
       <blank>  characters  in  strings  can  be included as is by preceding each <blank> with an
       escaping <backslash>.  More than one option can be set or listed by a single  set  command
       by  specifying  multiple  arguments,  each  separated from the next by one or more <blank>
       characters.

       See Edit Options in ex for details about specific options.

       Current line: Unchanged.

       Current column: Unchanged.

   Shell
       Synopsis:

                     sh[ell]

       Invoke the program named in the shell edit option with the single argument -i (interactive
       mode). Editing shall be resumed when the program exits.

       Current line: Unchanged.

       Current column: Unchanged.

   Source
       Synopsis:

                     so[urce] file

       Read  and  execute ex commands from file.  Lines in the file that are blank lines shall be
       ignored.

       Current line: As specified for the individual ex commands.

       Current column: As specified for the individual ex commands.

   Substitute
       Synopsis:

                     [2addr] s[ubstitute][/pattern/repl/[options][count][flags]]
                     [2addr] &[options][count][flags]]
                     [2addr] ~[options][count][flags]]

       Replace the first instance of the pattern pattern by the string  repl  on  each  specified
       line.  (See Regular Expressions in ex and Replacement Strings in ex.)  Any non-alphabetic,
       non-<blank> delimiter other than <backslash>, '|', <newline>, or double-quote can be  used
       instead  of  '/'.   <backslash>  characters  can be used to escape delimiters, <backslash>
       characters, and other special characters.

       The trailing delimiter can be omitted from pattern or from repl at the end of the  command
       line.  If  both  pattern  and repl are not specified or are empty (for example, "//"), the
       last s command shall be repeated. If only pattern is not specified or is empty,  the  last
       regular  expression  used  in the editor shall be used as the pattern. If only repl is not
       specified or is  empty,  the  pattern  shall  be  replaced  by  nothing.   If  the  entire
       replacement pattern is '%', the last replacement pattern to an s command shall be used.

       Entering  a  <carriage-return>  in repl (which requires an escaping <backslash> in ex mode
       and an escaping <control>‐V in open or vi mode)  shall  split  the  line  at  that  point,
       creating a new line in the edit buffer. The <carriage-return> shall be discarded.

       If  options includes the letter 'g' (global), all non-overlapping instances of the pattern
       in the line shall be replaced.

       If options includes the letter 'c' (confirm), then before each substitution the line shall
       be  written;  the  written line shall reflect all previous substitutions. On the following
       line, <space> characters shall be written beneath the characters from the  line  that  are
       before  the  pattern  to  be  replaced,  and '^' characters written beneath the characters
       included in the pattern to be replaced. The ex utility shall then wait for a response from
       the user. An affirmative response shall cause the substitution to be done, while any other
       input shall not make the substitution. An affirmative response shall  consist  of  a  line
       with  the  affirmative response (as defined by the current locale) at the beginning of the
       line. This line shall be subject to editing in the same way as the ex command line.

       If interrupted (see the ASYNCHRONOUS EVENTS section), any modifications confirmed  by  the
       user shall be preserved in the edit buffer after the interrupt.

       If the remembered search direction is not set, the s command shall set it to forward.

       In  the second Synopsis, the & command shall repeat the previous substitution, as if the &
       command were replaced by:

           s/pattern/repl/

       where pattern and repl are as specified in the previous s, &, or ~ command.

       In the third Synopsis, the ~ command shall repeat the previous substitution, as if the '~'
       were replaced by:

           s/pattern/repl/

       where pattern shall be the last regular expression specified to the editor, and repl shall
       be from the previous substitution (including & and ~) command.

       These commands shall be affected by the LC_MESSAGES environment variable.

       Current line: Set to the last line in which a substitution occurred, or, unchanged  if  no
       substitution occurred.

       Current column: Set to non-<blank>.

   Suspend
       Synopsis:

                     su[spend][!]
                     st[op][!]

       Allow  control  to  return  to  the invoking process; ex shall suspend itself as if it had
       received the SIGTSTP signal. The suspension shall occur only if job control is enabled  in
       the invoking shell (see the description of set -m).

       These commands shall be affected by the autowrite and writeany edit options.

       The current susp character (see stty) shall be equivalent to the suspend command.

   Tag
       Synopsis:

                     ta[g][!] tagstring

       The  results are unspecified if the format of a tags file is not as specified by the ctags
       utility (see ctags) description.

       The tag command shall search for tagstring in the tag files referred to by  the  tag  edit
       option,  in  the  order they are specified, until a reference to tagstring is found. Files
       shall be searched from beginning to end. If no reference is found, it shall  be  an  error
       and an error message to this effect shall be written. If the reference is not found, or if
       an error occurs while processing a file referred to in the tag edit option, it shall be an
       error, and an error message shall be written at the first occurrence of such an error.

       Otherwise, if the tags file contained a pattern, the pattern shall be treated as a regular
       expression used in the editor; for example, for the purposes of the s command.

       If the tagstring is in a file with a different name than the  current  pathname,  set  the
       current  pathname  to  the  name of that file, and replace the contents of the edit buffer
       with the contents of that file. In this case, if no '!'  is appended to the command  name,
       and the edit buffer has been modified since the last complete write, it shall be an error,
       unless the file is successfully written as specified by the autowrite option.

       This command shall be affected  by  the  autowrite,  tag,  taglength,  and  writeany  edit
       options.

       Current  line:  If  the tags file contained a line number, set to that line number. If the
       line number is larger than the last line in the edit buffer, an  error  message  shall  be
       written and the current line shall be set as specified for the edit command.

       If  the  tags  file contained a pattern, set to the first occurrence of the pattern in the
       file. If no matching pattern is found, an error message shall be written and  the  current
       line shall be set as specified for the edit command.

       Current  column:  If  the tags file contained a line-number reference and that line-number
       was not larger than the last line in the edit buffer, or if  the  tags  file  contained  a
       pattern  and  that pattern was found, set to non-<blank>.  Otherwise, set as specified for
       the edit command.

   Unabbreviate
       Synopsis:

                     una[bbrev] lhs

       If lhs is not an entry in the current list of abbreviations (see Abbreviate), it shall  be
       an error. Otherwise, delete lhs from the list of abbreviations.

       Current line: Unchanged.

       Current column: Unchanged.

   Undo
       Synopsis:

                     u[ndo]

       Reverse  the  changes  made  by  the  last  command that modified the contents of the edit
       buffer, including undo.  For this purpose, the global, v, open, and visual  commands,  and
       commands  resulting from buffer executions and mapped character expansions, are considered
       single commands.

       If no action that can be undone preceded the undo command, it shall be an error.

       If the undo command restores lines that were marked,  the  mark  shall  also  be  restored
       unless it was reset subsequent to the deletion of the lines.

       Current line:

        1. If lines are added or changed in the file, set to the first line added or changed.

        2. Set to the line before the first line deleted, if it exists.

        3. Set to 1 if the edit buffer is not empty.

        4. Set to zero.

       Current column: Set to non-<blank>.

   Unmap
       Synopsis:

                     unm[ap][!] lhs

       If  '!'   is  appended to the command name, and if lhs is not an entry in the list of text
       input mode map definitions, it shall be an error. Otherwise, delete lhs from the  list  of
       text input mode map definitions.

       If  no  '!'   is  appended  to the command name, and if lhs is not an entry in the list of
       command mode map definitions, it shall be an error. Otherwise, delete lhs from the list of
       command mode map definitions.

       Current line: Unchanged.

       Current column: Unchanged.

   Version
       Synopsis:

                     ve[rsion]

       Write  a  message containing version information for the editor. The format of the message
       is unspecified.

       Current line: Unchanged.

       Current column: Unchanged.

   Visual
       Synopsis:

                     [1addr] vi[sual][type][count][flags]

       If ex is currently in open or visual mode, the Synopsis and behavior of the visual command
       shall be the same as the edit command, as specified by Edit.

       Otherwise,  this  command  need not be supported on block-mode terminals or terminals with
       insufficient capabilities. If standard input, standard output, or standard error  are  not
       terminal devices, the results are unspecified.

       If  count  is  specified,  the  value  of the window edit option shall be set to count (as
       described in window).  If the '^' type character  was  also  specified,  the  window  edit
       option shall be set before being used by the type character.

       Enter  visual  mode.  If  type  is  not  specified,  it  shall  be as if a type of '+' was
       specified. The type shall cause the following effects:

       +     Place the beginning of the specified line at the top of the display.

       -     Place the end of the specified line at the bottom of the display.

       .     Place the beginning of the specified line in the middle of the display.

       ^     If the specified line is less than or equal to the value of the window edit  option,
             set  the  line  to  1; otherwise, decrement the line by the value of the window edit
             option minus 1. Place the beginning of this line as  close  to  the  bottom  of  the
             displayed  lines  as  possible,  while still displaying the value of the window edit
             option number of lines.

       Current line: Set to the specified line.

       Current column: Set to non-<blank>.

   Write
       Synopsis:

                     [2addr] w[rite][!][>>][file]
                     [2addr] w[rite][!][file]
                     [2addr] wq[!][>>][file]

       If no lines are specified, the lines shall default to the entire file.

       The command wq shall be equivalent to a write command followed  by  a  quit  command;  wq!
       shall  be  equivalent  to  write!   followed by quit.  In both cases, if the write command
       fails, the quit shall not be attempted.

       If the command name is not followed by one or more <blank>  characters,  or  file  is  not
       preceded by a '!'  character, the write shall be to a file.

        1. If  the  >>  argument  is  specified,  and the file already exists, the lines shall be
           appended to the file instead  of  replacing  its  contents.  If  the  >>  argument  is
           specified,  and  the  file does not already exist, it is unspecified whether the write
           shall proceed as if the >> argument had not been specified or if the write shall fail.

        2. If the readonly edit option is set (see readonly), the write shall fail.

        3. If file is specified, and is not the current pathname, and the file exists, the  write
           shall fail.

        4. If  file  is not specified, the current pathname shall be used. If there is no current
           pathname, the write command shall fail.

        5. If the current pathname is used, and the current pathname has been changed by the file
           or  read  commands,  and  the  file  exists,  the  write  shall  fail. If the write is
           successful, subsequent writes shall not fail  for  this  reason  (unless  the  current
           pathname is changed again).

        6. If  the whole edit buffer is not being written, and the file to be written exists, the
           write shall fail.

       For rules 1., 2., 3., and 5., the write can be forced by appending the character  '!'   to
       the command name.

       For rules 2., 3., and 5., the write can be forced by setting the writeany edit option.

       Additional, implementation-defined tests may cause the write to fail.

       If the edit buffer is empty, a file without any contents shall be written.

       An informational message shall be written noting the number of lines and bytes written.

       Otherwise,  if  the command is followed by one or more <blank> characters, and the file is
       preceded by '!', the rest of the line  after  the  '!'   shall  have  '%',  '#',  and  '!'
       characters expanded as described in Command Line Parsing in ex.

       The  ex  utility  shall  then  pass  two  arguments to the program named by the shell edit
       option; the first shall be -c and the second shall be the expanded arguments to the  write
       command  as  a single argument. The specified lines shall be written to the standard input
       of the command. The standard error and standard output of the program, if  any,  shall  be
       written  as described for the print command. If the last character in that output is not a
       <newline>, a <newline> shall be written at the end of the output.

       The special meaning of the '!'  following the write command can be overridden by  escaping
       it with a <backslash> character.

       Current line: Unchanged.

       Current column: Unchanged.

   Write and Exit
       Synopsis:

                     [2addr] x[it][!][file]

       If  the  edit  buffer  has  not  been modified since the last complete write, xit shall be
       equivalent to the quit command, or if a '!'  is appended to the command name, to quit!.

       Otherwise, xit shall be equivalent to the wq command, or if a  '!'   is  appended  to  the
       command name, to wq!.

       Current line: Unchanged.

       Current column: Unchanged.

   Yank
       Synopsis:

                     [2addr] ya[nk][buffer][count]

       Copy  the  specified lines to the specified buffer (by default, the unnamed buffer), which
       shall become a line-mode buffer.

       Current line: Unchanged.

       Current column: Unchanged.

   Adjust Window
       Synopsis:

                     [1addr] z[!][type ...][count][flags]

       If no line is specified, the current line shall be the default;  if  type  is  omitted  as
       well,  the current line value shall first be incremented by 1. If incrementing the current
       line would cause it to be greater than the last line in the edit buffer, it  shall  be  an
       error.

       If there are <blank> characters between the type argument and the preceding z command name
       or optional '!'  character, it shall be an error.

       If count is specified, the value of the window edit option  shall  be  set  to  count  (as
       described  in  window).  If count is omitted, it shall default to 2 times the value of the
       scroll edit option, or if !  was specified, the number of lines in the display minus 1.

       If type is omitted, then count lines starting with the specified line  shall  be  written.
       Otherwise,  count  lines  starting  with  the line specified by the type argument shall be
       written.

       The type argument shall change the lines to be written. The possible values of type are as
       follows:

       -     The specified line shall be decremented by the following value:

                 (((number of '-' characters) x count) -1)

             If the calculation would result in a number less than 1, it shall be an error. Write
             lines from the edit buffer, starting at the new value of line, until count lines  or
             the last line in the edit buffer has been written.

       +     The specified line shall be incremented by the following value:

                 (((number of '+' characters) -1) x count) +1

             If  the  calculation would result in a number greater than the last line in the edit
             buffer, it shall be an error. Write lines from the edit buffer, starting at the  new
             value  of  line,  until  count  lines  or  the last line in the edit buffer has been
             written.

       =,.   If more than a single '.'  or '=' is specified, it shall be an error. The  following
             steps shall be taken:

              1. If count is zero, nothing shall be written.

              2. Write  as  many  of  the  N  lines before the current line in the edit buffer as
                 exist. If count or '!'  was specified, N shall be:

                     (count -1) /2

                 Otherwise, N shall be:

                     (count -3) /2

                 If N is a number less than 3, no lines shall be written.

              3. If '=' was specified as the type character,  write  a  line  consisting  of  the
                 smaller  of  the  number  of  columns  in  the display divided by two, or 40 '-'
                 characters.

              4. Write the current line.

              5. Repeat step 3.

              6. Write as many of the N lines after the current line in the edit buffer as exist.
                 N shall be defined as in step 2. If N is a number less than 3, no lines shall be
                 written. If count is less than 3, no lines shall be written.

       ^     The specified line shall be decremented by the following value:

                 (((number of '^' characters) +1) x count) -1

             If the calculation would result in a number less than 1, it shall be an error. Write
             lines  from the edit buffer, starting at the new value of line, until count lines or
             the last line in the edit buffer has been written.

       Current line: Set to the last line written, unless the type is =, in which  case,  set  to
       the specified line.

       Current column: Set to non-<blank>.

   Escape
       Synopsis:

                     ! command
                     [addr]! command

       The  contents of the line after the '!'  shall have '%', '#', and '!'  characters expanded
       as described in Command Line Parsing in ex.  If the expansion causes the text of the  line
       to change, it shall be redisplayed, preceded by a single '!'  character.

       The ex utility shall execute the program named by the shell edit option. It shall pass two
       arguments to the program; the first shall be -c, and the  second  shall  be  the  expanded
       arguments to the !  command as a single argument.

       If  no lines are specified, the standard input, standard output, and standard error of the
       program shall be set to the standard input, standard output, and standard error of the  ex
       program  when  it was invoked. In addition, a warning message shall be written if the edit
       buffer has been modified since the last complete write, and the warn edit option is set.

       If lines are specified, they shall be passed to the program as  standard  input,  and  the
       standard  output  and  standard error of the program shall replace those lines in the edit
       buffer. Each line in the program output (as delimited by <newline> characters or  the  end
       of  the output if it is not immediately preceded by a <newline>), shall be a separate line
       in the edit buffer. Any occurrences of <carriage-return> and <newline> pairs in the output
       shall  be treated as single <newline> characters. The specified lines shall be copied into
       the unnamed buffer before they are replaced, and the unnamed buffer shall become  a  line-
       mode buffer.

       If in ex mode, a single '!'  character shall be written when the program completes.

       This  command  shall  be  affected  by  the  shell  and warn edit options. If no lines are
       specified, this command shall be affected by the autowrite and writeany edit  options.  If
       lines are specified, this command shall be affected by the autoprint edit option.

       Current line:

        1. If no lines are specified, unchanged.

        2. Otherwise, set to the last line read in, if any lines are read in.

        3. Otherwise,  set to the line before the first line of the lines specified, if that line
           exists.

        4. Otherwise, set to the first line of the edit buffer if the edit buffer is not empty.

        5. Otherwise, set to zero.

       Current column: If no lines are specified, unchanged. Otherwise, set to non-<blank>.

   Shift Left
       Synopsis:

                     [2addr] <[< ...][count][flags]

       Shift the specified lines to the start of the line; the number of column positions  to  be
       shifted  shall  be the number of command characters times the value of the shiftwidth edit
       option. Only leading <blank> characters shall be deleted or  changed  into  other  <blank>
       characters in shifting; other characters shall not be affected.

       Lines  to  be  shifted shall be copied into the unnamed buffer, which shall become a line-
       mode buffer.

       This command shall be affected by the autoprint edit option.

       Current line: Set to the last line in the lines specified.

       Current column: Set to non-<blank>.

   Shift Right
       Synopsis:

                     [2addr] >[> ...][count][flags]

       Shift the specified lines away from the start of the line; the number of column  positions
       to  be shifted shall be the number of command characters times the value of the shiftwidth
       edit option. The shift shall be accomplished by adding <blank> characters as a  prefix  to
       the line or changing leading <blank> characters into other <blank> characters. Empty lines
       shall not be changed.

       Lines to be shifted shall be copied into the unnamed buffer, which shall  become  a  line-
       mode buffer.

       This command shall be affected by the autoprint edit option.

       Current line: Set to the last line in the lines specified.

       Current column: Set to non-<blank>.

   <control>‐D
       Synopsis:

                     <control>-D

       Write the next n lines, where n is the minimum of the values of the scroll edit option and
       the number of lines after the current line in the edit buffer. If the current line is  the
       last line of the edit buffer it shall be an error.

       Current line: Set to the last line written.

       Current column: Set to non-<blank>.

   Write Line Number
       Synopsis:

                     [1addr] = [flags]

       If line is not specified, it shall default to the last line in the edit buffer.  Write the
       line number of the specified line.

       Current line: Unchanged.

       Current column: Unchanged.

   Execute
       Synopsis:

                     [2addr] @ buffer
                     [2addr] * buffer

       If no buffer is specified or is specified as '@' or '*', the last buffer executed shall be
       used. If no previous buffer has been executed, it shall be an error.

       For  each  line  specified  by the addresses, set the current line ('.')  to the specified
       line, and execute the contents of the named buffer (as they were at the time the @ command
       was  executed)  as  ex commands. For each line of a line-mode buffer, and all but the last
       line of a character-mode buffer, the ex command parser shall behave as  if  the  line  was
       terminated by a <newline>.

       If  an  error  occurs  during  this process, or a line specified by the addresses does not
       exist when the current line would be set to it, or more than a single line  was  specified
       by the addresses, and the contents of the edit buffer are replaced (for example, by the ex
       :edit command) an error message shall be written, and no more commands resulting from  the
       execution of this command shall be processed.

       Current line: As specified for the individual ex commands.

       Current column: As specified for the individual ex commands.

   Regular Expressions in ex
       The  ex utility shall support regular expressions that are a superset of the basic regular
       expressions described in the Base Definitions volume of POSIX.1‐2017, Section  9.3,  Basic
       Regular  Expressions.   A  null  regular expression ("//") shall be equivalent to the last
       regular expression encountered.

       Regular expressions can be used in addresses to specify lines and, in some  commands  (for
       example, the substitute command), to specify portions of a line to be substituted.

       The following constructs can be used to enhance the basic regular expressions:

       \<    Match  the  beginning  of  a  word.  (See the definition of word at the beginning of
             Command Descriptions in ex.)

       \>    Match the end of a word.

       ~     Match the replacement part  of  the  last  substitute  command.  The  <tilde>  ('~')
             character  can  be escaped in a regular expression to become a normal character with
             no special meaning. The <backslash> shall be discarded.

       When the editor option magic is not set, the only characters with special  meanings  shall
       be  '^'  at the beginning of a pattern, '$' at the end of a pattern, and <backslash>.  The
       characters '.', '*', '[', and '~' shall be treated as ordinary characters unless  preceded
       by  a <backslash>; when preceded by a <backslash> they shall regain their special meaning,
       or in the case of <backslash>, be handled as a single <backslash>.  <backslash> characters
       used to escape other characters shall be discarded.

   Replacement Strings in ex
       The  character  '&' ('\&' if the editor option magic is not set) in the replacement string
       shall stand for the text matched by the pattern to be replaced. The character '~' ('\~' if
       magic  is  not  set)  shall be replaced by the replacement part of the previous substitute
       command. The sequence '\n', where n is an integer, shall be replaced by the  text  matched
       by  the  corresponding  back-reference  expression.  If  the  corresponding back-reference
       expression does not match, then the characters '\n' shall be replaced by the empty string.

       The strings '\l', '\u', '\L', and '\U' can be used to modify the case of elements  in  the
       replacement  string  (using  the  '\&' or "\"digit) notation. The string '\l' ('\u') shall
       cause the character that follows to be converted to lowercase (uppercase). The string '\L'
       ('\U')  shall  cause  all  characters  subsequent  to  it  to  be  converted  to lowercase
       (uppercase) as they are inserted by the substitution until the string '\e' or '\E', or the
       end of the replacement string, is encountered.

       Otherwise,  any  character  following  a  <backslash>  shall  be  treated  as that literal
       character, and the escaping <backslash> shall be discarded.

       An example of case conversion with the s command is as follows:

           :p
           The cat sat on the mat.
           :s/\<.at\>/\u&/gp
           The Cat Sat on the Mat.
           :s/S\(.*\)M/S\U\1\eM/p
           The Cat SAT ON THE Mat.

   Edit Options in ex
       The ex utility has a number of options  that  modify  its  behavior.  These  options  have
       default settings, which can be changed using the set command.

       Options are Boolean unless otherwise specified.

   autoindent, ai
       [Default unset]

       If autoindent is set, each line in input mode shall be indented (using first as many <tab>
       characters as possible, as determined by the editor option tabstop, and then using <space>
       characters) to align with another line, as follows:

        1. If  in  open or visual mode and the text input is part of a line-oriented command (see
           the EXTENDED DESCRIPTION in vi), align to the first column.

        2. Otherwise, if in open or visual mode, indentation  for  each  line  shall  be  set  as
           follows:

            a. If  a line was previously inserted as part of this command, it shall be set to the
               indentation of the last inserted line by default, or as  otherwise  specified  for
               the <control>‐D character in Input Mode Commands in vi.

            b. Otherwise,  it  shall  be  set to the indentation of the previous current line, if
               any; otherwise, to the first column.

        3. For the ex a, i, and c commands, indentation for each line shall be set as follows:

            a. If a line was previously inserted as part of this command, it shall be set to  the
               indentation  of  the  last inserted line by default, or as otherwise specified for
               the eof character in Scroll.

            b. Otherwise, if the command is the ex a  command,  it  shall  be  set  to  the  line
               appended after, if any; otherwise to the first column.

            c. Otherwise,  if  the  command  is  the  ex  i  command, it shall be set to the line
               inserted before, if any; otherwise to the first column.

            d. Otherwise, if the command is the ex c command, it shall be set to the  indentation
               of the line replaced.

   autoprint, ap
       [Default set]

       If autoprint is set, the current line shall be written after each ex command that modifies
       the contents of the current edit buffer, and after each tag  command  for  which  the  tag
       search pattern was found or tag line number was valid, unless:

        1. The command was executed while in open or visual mode.

        2. The command was executed as part of a global or v command or @ buffer execution.

        3. The command was the form of the read command that reads a file into the edit buffer.

        4. The command was the append, change, or insert command.

        5. The command was not terminated by a <newline>.

        6. The  current  line  shall  be written by a flag specified to the command; for example,
           delete # shall write the current line as specified for the flag modifier to the delete
           command, and not as specified by the autoprint edit option.

   autowrite, aw
       [Default unset]

       If  autowrite  is  set, and the edit buffer has been modified since it was last completely
       written to any file, the contents of the edit buffer shall be written as if the  ex  write
       command  had  been  specified  without  arguments,  before  each  command  affected by the
       autowrite edit option is executed. Appending the character '!'  to the command name of any
       of the ex commands except '!'  shall prevent the write. If the write fails, it shall be an
       error and the command shall not be executed.

   beautify, bf
       [Default unset]

       If beautify is set, all non-printable characters, other than <tab>, <newline>, and  <form-
       feed> characters, shall be discarded from text read in from files.

   directory, dir
       [Default implementation-defined]

       The  value  of  this  option  specifies  the directory in which the editor buffer is to be
       placed. If this directory is not writable by the user, the editor shall quit.

   edcompatible, ed
       [Default unset]

       Causes the presence of g and c suffixes on  substitute  commands  to  be  remembered,  and
       toggled by repeating the suffixes.

   errorbells, eb
       [Default unset]

       If  the  editor  is in ex mode, and the terminal does not support a standout mode (such as
       inverse video), and errorbells is set, error messages shall be preceded  by  alerting  the
       terminal.

   exrc
       [Default unset]

       If  exrc  is set, ex shall access any .exrc file in the current directory, as described in
       Initialization in ex and vi.  If exrc is not set, ex shall ignore any .exrc  file  in  the
       current directory during initialization, unless the current directory is that named by the
       HOME environment variable.

   ignorecase, ic
       [Default unset]

       If ignorecase is set, characters that have uppercase and lowercase  representations  shall
       have  those  representations  considered  as equivalent for purposes of regular expression
       comparison.

       The ignorecase edit option shall affect all remembered regular expressions;  for  example,
       unsetting  the  ignorecase edit option shall cause a subsequent vi n command to search for
       the last basic regular expression in a case-sensitive fashion.

   list
       [Default unset]

       If list is set, edit buffer lines written while in ex command mode  shall  be  written  as
       specified  for  the  print command with the l flag specified. In open or visual mode, each
       edit buffer line shall be displayed as specified for the ex print command with the l  flag
       specified.  In  open  or  visual  text  input  mode,  when the cursor does not rest on any
       character in the line, it shall rest on the '$' marking the end of the line.

   magic
       [Default set]

       If magic is set, modify the  interpretation  of  characters  in  regular  expressions  and
       substitution replacement strings (see Regular Expressions in ex and Replacement Strings in
       ex).

   mesg
       [Default set]

       If mesg is set, the permission for others to use the write or talk commands  to  write  to
       the terminal shall be turned on while in open or visual mode. The shell-level command mesg
       n shall take precedence over any setting of the ex mesg option; that is,  if  mesg  y  was
       issued before the editor started (or in a shell escape), such as:

           :!mesg y

       the  mesg  option  in  ex  shall suppress incoming messages, but the mesg option shall not
       enable incoming messages if mesg n was issued.

   number, nu
       [Default unset]

       If number is set, edit buffer lines written while in ex command mode shall be written with
       line  numbers,  in the format specified by the print command with the # flag specified. In
       ex text input mode, each line shall be preceded by the line number it  will  have  in  the
       file.

       In  open  or  visual  mode, each edit buffer line shall be displayed with a preceding line
       number, in the format specified by the ex print command with the #  flag  specified.  This
       line  number  shall  not be considered part of the line for the purposes of evaluating the
       current column; that is, column position 1 shall be the first column  position  after  the
       format specified by the print command.

   paragraphs, para
       [Default in the POSIX locale IPLPPPQPP LIpplpipbp]

       The  paragraphs  edit option shall define additional paragraph boundaries for the open and
       visual mode commands. The paragraphs  edit  option  can  be  set  to  a  character  string
       consisting  of  zero  or  more  character  pairs. It shall be an error to set it to an odd
       number of characters.

   prompt
       [Default set]

       If prompt is set, ex command mode input shall be prompted for with a <colon>  (':');  when
       unset, no prompt shall be written.

   readonly
       [Default see text]

       If  the  readonly  edit  option  is set, read-only mode shall be enabled (see Write).  The
       readonly edit option shall be initialized to set if either of the following conditions are
       true:

        *  The command-line option -R was specified.

        *  Performing  actions  equivalent  to  the  access()  function called with the following
           arguments indicates that the file lacks write permission:

            1. The current pathname is used as the path argument.

            2. The constant W_OK is used as the amode argument.

       The readonly edit option may be  initialized  to  set  for  other,  implementation-defined
       reasons.  The  readonly edit option shall not be initialized to unset based on any special
       privileges of the user or process. The readonly edit option shall  be  reinitialized  each
       time  that  the  contents of the edit buffer are replaced (for example, by an edit or next
       command) unless the user has explicitly set it, in which case it shall  remain  set  until
       the  user explicitly unsets it. Once unset, it shall again be reinitialized each time that
       the contents of the edit buffer are replaced.

   redraw
       [Default unset]

       The editor simulates an intelligent terminal on a dumb terminal.  (Since this is likely to
       require  a  large amount of output to the terminal, it is useful only at high transmission
       speeds.)

   remap
       [Default set]

       If remap is set, map translation shall allow for maps defined  in  terms  of  other  maps;
       translation  shall  continue  until a final product is obtained. If unset, only a one-step
       translation shall be done.

   report
       [Default 5]

       The value of this report edit option specifies what number of lines being  added,  copied,
       deleted,  or modified in the edit buffer will cause an informational message to be written
       to the user. The following conditions shall cause an informational  message.  The  message
       shall  contain  the  number of lines added, copied, deleted, or modified, but is otherwise
       unspecified.

        *  An ex or vi editor command, other than open, undo, or visual, that modifies  at  least
           the  value  of  the report edit option number of lines, and which is not part of an ex
           global or v command, or ex or  vi  buffer  execution,  shall  cause  an  informational
           message to be written.

        *  An  ex  yank  or  vi y or Y command, that copies at least the value of the report edit
           option plus 1 number of lines, and which is not part of an ex global or v command,  or
           ex or vi buffer execution, shall cause an informational message to be written.

        *  An ex global, v, open, undo, or visual command or ex or vi buffer execution, that adds
           or deletes a total of at least the value of the report edit option  number  of  lines,
           and  which  is  not  part  of an ex global or v command, or ex or vi buffer execution,
           shall cause an informational message to be written.  (For example,  if  3  lines  were
           added  and 8 lines deleted during an ex visual command, 5 would be the number compared
           against the report edit option after the command completed.)

   scroll, scr
       [Default (number of lines in the display -1)/2]

       The value of the scroll edit option shall determine the number of lines scrolled by the ex
       <control>‐D  and  z commands. For the vi <control>‐D and <control>‐U commands, it shall be
       the initial number of lines to scroll when no previous <control>‐D or <control>‐U  command
       has been executed.

   sections
       [Default in the POSIX locale NHSHH HUnhsh]

       The  sections  edit  option  shall  define  additional section boundaries for the open and
       visual mode commands. The sections edit option can be set to a character string consisting
       of  zero  or  more  character  pairs;  it  shall be an error to set it to an odd number of
       characters.

   shell, sh
       [Default from the environment variable SHELL]

       The value of this option shall be a string. The default shall  be  taken  from  the  SHELL
       environment  variable. If the SHELL environment variable is null or empty, the sh (see sh)
       utility shall be the default.

   shiftwidth, sw
       [Default 8]

       The value of this option shall give the width in columns  of  an  indentation  level  used
       during autoindentation and by the shift commands (< and >).

   showmatch, sm
       [Default unset]

       The  functionality described for the showmatch edit option need not be supported on block-
       mode terminals or terminals with insufficient capabilities.

       If showmatch is set, in open or visual mode, when a ')' or '}' is typed, if  the  matching
       '('  or  '{' is currently visible on the display, the matching '(' or '{' shall be flagged
       moving the cursor to its location for an unspecified amount of time.

   showmode
       [Default unset]

       If showmode is set, in open or visual mode, the current mode that the editor is  in  shall
       be  displayed  on  the last line of the display. Command mode and text input mode shall be
       differentiated; other unspecified modes  and  implementation-defined  information  may  be
       displayed.

   slowopen
       [Default unset]

       If  slowopen  is  set during open and visual text input modes, the editor shall not update
       portions of the display other than those display line columns that display the  characters
       entered by the user (see Input Mode Commands in vi).

   tabstop, ts
       [Default 8]

       The  value  of  this  edit option shall specify the column boundary used by a <tab> in the
       display (see autoprint, ap and Input Mode Commands in vi).

   taglength, tl
       [Default zero]

       The value of this edit option shall specify the maximum  number  of  characters  that  are
       considered  significant  in  the user-specified tag name and in the tag name from the tags
       file. If the value is zero, all characters in both tag names shall be significant.

   tags
       [Default see text]

       The value of this edit option shall be a string of <blank>-delimited  pathnames  of  files
       used by the tag command. The default value is unspecified.

   term
       [Default from the environment variable TERM]

       The  value of this edit option shall be a string. The default shall be taken from the TERM
       variable in the environment. If the TERM  environment  variable  is  empty  or  null,  the
       default  is  unspecified.  The editor shall use the value of this edit option to determine
       the type of the display device.

       The results are unspecified if the user changes the value of the term  edit  option  after
       editor initialization.

   terse
       [Default unset]

       If  terse  is  set,  error  messages may be less verbose. However, except for this caveat,
       error messages are unspecified. Furthermore,  not  all  error  messages  need  change  for
       different settings of this option.

   warn
       [Default set]

       If  warn  is  set,  and the contents of the edit buffer have been modified since they were
       last completely written, the editor  shall  write  a  warning  message  before  certain  !
       commands (see Escape).

   window
       [Default see text]

       A value used in open and visual mode, by the <control>‐B and <control>‐F commands, and, in
       visual mode, to specify the number of lines displayed when the screen is repainted.

       If the -w command-line option is not specified, the default value  shall  be  set  to  the
       value  of  the  LINES  environment variable. If the LINES environment variable is empty or
       null, the default shall be the number of lines in the display minus 1.

       Setting the window edit option to zero or to a value greater than the number of  lines  in
       the  display minus 1 (either explicitly or based on the -w option or the LINES environment
       variable) shall cause the window edit option to be set to  the  number  of  lines  in  the
       display minus 1.

       The  baud  rate  of  the terminal line may change the default in an implementation-defined
       manner.

   wrapmargin, wm
       [Default 0]

       If the value of this edit option is zero, it shall have no effect.

       If not in the POSIX locale, the effect of this edit option is implementation-defined.

       Otherwise, it shall specify a number of columns from the ending margin of the terminal.

       During open and visual text input modes, for each character for  which  any  part  of  the
       character  is  displayed  in a column that is less than wrapmargin columns from the ending
       margin of the display line, the editor shall behave as follows:

        1. If the character triggering this event is a <blank>, it, and all immediately preceding
           <blank>  characters  on  the  current line entered during the execution of the current
           text input command, shall be discarded, and the editor shall behave as if the user had
           entered a single <newline> instead. In addition, if the next user-entered character is
           a <space>, it shall be discarded as well.

        2. Otherwise, if there are one or more <blank> characters on the current line immediately
           preceding  the  last group of inserted non-<blank> characters which was entered during
           the execution of the current text input  command,  the  <blank>  characters  shall  be
           replaced as if the user had entered a single <newline> instead.

       If  the autoindent edit option is set, and the events described in 1. or 2. are performed,
       any <blank> characters at or after the cursor in the current line shall be discarded.

       The ending margin shall be determined  by  the  system  or  overridden  by  the  user,  as
       described for COLUMNS in the ENVIRONMENT VARIABLES section and the Base Definitions volume
       of POSIX.1‐2017, Chapter 8, Environment Variables.

   wrapscan, ws
       [Default set]

       If wrapscan is set, searches (the ex / or ?  addresses, or open and visual mode /,  ?,  N,
       and  n  commands)  shall  wrap around the beginning or end of the edit buffer; when unset,
       searches shall stop at the beginning or end of the edit buffer.

   writeany, wa
       [Default unset]

       If writeany is set, some of the checks performed when  executing  the  ex  write  commands
       shall be inhibited, as described in editor option autowrite.

EXIT STATUS

       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.

CONSEQUENCES OF ERRORS

       When  any  error  is  encountered and the standard input is not a terminal device file, ex
       shall not write the file or return to command or text input mode, and shall terminate with
       a non-zero exit status.

       Otherwise,  when an unrecoverable error is encountered, it shall be equivalent to a SIGHUP
       asynchronous event.

       Otherwise, when an error is encountered, the editor shall behave as specified  in  Command
       Line Parsing in ex.

       The following sections are informative.

APPLICATION USAGE

       If  a  SIGSEGV  signal  is  received  while  ex  is  saving  a file, the file might not be
       successfully saved.

       The next command can accept more than one file, so usage such as:

           next `ls [abc]*`

       is valid; it would not be valid for the edit or read commands, for example,  because  they
       expect only one file and unspecified results occur.

EXAMPLES

       None.

RATIONALE

       The  ex/vi specification is based on the historical practice found in the 4 BSD and System
       V implementations of ex and vi.

       A restricted editor (both the  historical  red  utility  and  modifications  to  ex)  were
       considered  and rejected for inclusion. Neither option provided the level of security that
       users might expect.

       It is recognized that ex visual mode and related  features  would  be  difficult,  if  not
       impossible,  to  implement  satisfactorily on a block-mode terminal, or a terminal without
       any form of cursor addressing; thus, it is not a mandatory requirement that such  features
       should  work  on  all  terminals.  It is the intention, however, that an ex implementation
       should provide the full set of capabilities on all terminals capable of supporting them.

   Options
       The -c replacement for +command was inspired by the -e option of sed.   Historically,  all
       such  commands  (see  edit  and next as well) were executed from the last line of the edit
       buffer. This meant, for example, that "+/pattern" would fail unless  the  wrapscan  option
       was  set. POSIX.1‐2008 requires conformance to historical practice. The +command option is
       no  longer  specified  by  POSIX.1‐2008  but  may  be  present  in  some  implementations.
       Historically, some implementations restricted the ex commands that could be listed as part
       of the command line arguments.   For  consistency,  POSIX.1‐2008  does  not  permit  these
       restrictions.

       In  historical implementations of the editor, the -R option (and the readonly edit option)
       only prevented overwriting of files; appending  to  files  was  still  permitted,  mapping
       loosely  into the csh noclobber variable. Some implementations, however, have not followed
       this semantic, and readonly does not permit appending  either.  POSIX.1‐2008  follows  the
       latter practice, believing that it is a more obvious and intuitive meaning of readonly.

       The  -s  option suppresses all interactive user feedback and is useful for editing scripts
       in batch jobs. The list of specific effects is  historical  practice.  The  terminal  type
       ``incapable of supporting open and visual modes'' has historically been named ``dumb''.

       The  -t  option  was  required  because  the ctags utility appears in POSIX.1‐2008 and the
       option is available in all historical implementations of ex.

       Historically, the ex and vi utilities accepted a -x option, which did encryption based  on
       the algorithm found in the historical crypt utility. The -x option for encryption, and the
       associated crypt utility, were omitted because the algorithm used was not specifiable  and
       the  export  control  laws  of  some  nations  make  it  difficult to export cryptographic
       technology. In addition, it did not historically provide the level of security that  users
       might expect.

   Standard Input
       An  end-of-file condition is not equivalent to an end-of-file character.  A common end-of-
       file character, <control>‐D, is historically an ex command.

       There was no maximum line length in historical implementations of ex.  Specifically, as it
       was  parsed  in  chunks,  the addresses had a different maximum length than the filenames.
       Further, the maximum line buffer size was declared as BUFSIZ, which was different  lengths
       on different systems. This version selected the value of {LINE_MAX} to impose a reasonable
       restriction on portable usage of ex and to aid test suite writers in their development  of
       realistic tests that exercise this limit.

   Input Files
       It  was  an  explicit decision by the standard developers that a <newline> be added to any
       file lacking one. It was believed that this feature of ex and vi was relied on by users in
       order to make text files lacking a trailing <newline> more portable. It is recognized that
       this will require a user-specified option or extension for implementations that permit  ex
       and vi to edit files of type other than text if such files are not otherwise identified by
       the system. It was agreed that the ability to edit files of arbitrary type can be  useful,
       but it was not considered necessary to mandate that an ex or vi implementation be required
       to handle files other than text files.

       The paragraph in the INPUT FILES section, ``By default, ...'',  is  intended  to  close  a
       long-standing  security  problem  in  ex and vi; that of the ``modeline'' or ``modelines''
       edit option. This feature allows any line in the first or last  five  lines  of  the  file
       containing  the  strings  "ex:"  or  "vi:"  (and, apparently, "ei:" or "vx:") to be a line
       containing editor commands, and ex interprets all the text up to the next ':' or <newline>
       as  a command. Consider the consequences, for example, of an unsuspecting user using ex or
       vi as the editor when replying to a mail message in which a line such as:

           ex:! rm -rf :

       appeared in the signature lines. The standard developers believed strongly that an  editor
       should  not by default interpret any lines of a file. Vendors are strongly urged to delete
       this feature from their implementations of ex and vi.

   Asynchronous Events
       The intention of the phrase ``complete write'' is that the entire edit buffer  be  written
       to stable storage. The note regarding temporary files is intended for implementations that
       use temporary files to back edit buffers unnamed by the user.

       Historically, SIGQUIT was ignored by ex, but was the equivalent of the Q command in visual
       mode;  that  is, it exited visual mode and entered ex mode. POSIX.1‐2008 permits, but does
       not require, this behavior. Historically, SIGINT was often used by vi users  to  terminate
       text  input  mode (<control>‐C is often easier to enter than <ESC>).  Some implementations
       of vi alerted the terminal on this event, and some did  not.  POSIX.1‐2008  requires  that
       SIGINT behave identically to <ESC>, and that the terminal not be alerted.

       Historically,  suspending  the  ex editor during text input mode was similar to SIGINT, as
       completed lines were retained, but any partial line discarded, and the editor returned  to
       command  mode.  POSIX.1‐2008  is  silent  on this issue; implementations are encouraged to
       follow historical practice, where possible.

       Historically, the vi editor did not treat SIGTSTP as an asynchronous  event,  and  it  was
       therefore impossible to suspend the editor in visual text input mode.  There are two major
       reasons for this. The first is that SIGTSTP is a broadcast signal on UNIX systems, and the
       chain  of  events  where  the shell execs an application that then execs vi usually caused
       confusion for the terminal state if SIGTSTP was delivered to  the  process  group  in  the
       default  manner.  The  second was that most implementations of the UNIX curses package did
       not handle SIGTSTP safely, and the receipt of SIGTSTP at the wrong time would  cause  them
       to  crash.  POSIX.1‐2008  is silent on this issue; implementations are encouraged to treat
       suspension as an asynchronous event if possible.

       Historically, modifications to the edit buffer made before SIGINT interrupted an operation
       were  retained;  that is, anywhere from zero to all of the lines to be modified might have
       been modified by the time the SIGINT arrived. These changes  were  not  discarded  by  the
       arrival  of  SIGINT.  POSIX.1‐2008  permits this behavior, noting that the undo command is
       required to be able to undo these partially completed commands.

       The action  taken  for  signals  other  than  SIGINT,  SIGCONT,  SIGHUP,  and  SIGTERM  is
       unspecified because some implementations attempt to save the edit buffer in a useful state
       when other signals are received.

   Standard Error
       For ex/vi, diagnostic messages are those messages reported as a result of a failed attempt
       to  invoke  ex  or  vi,  such as invalid options or insufficient resources, or an abnormal
       termination condition. Diagnostic messages should not be confused with the error  messages
       generated by inappropriate or illegal user commands.

   Initialization in ex and vi
       If an ex command (other than cd, chdir, or source) has a filename argument, one or both of
       the alternate and current pathnames will be set. Informally, they are set as follows:

        1. If the ex command is one that replaces  the  contents  of  the  edit  buffer,  and  it
           succeeds,  the  current  pathname  will  be  set  to  the filename argument (the first
           filename argument in the case of the next command) and the alternate pathname will  be
           set to the previous current pathname, if there was one.

        2. In  the  case of the file read/write forms of the read and write commands, if there is
           no current pathname, the current pathname will be set to the filename argument.

        3. Otherwise, the alternate pathname will be set to the filename argument.

       For example, :edit foo and :recover foo, when successful, set the current  pathname,  and,
       if  there  was  a  previous current pathname, the alternate pathname. The commands :write,
       !command, and :edit set neither the current or  alternate  pathnames.  If  the  :edit  foo
       command  were  to  fail for some reason, the alternate pathname would be set. The read and
       write commands set the alternate pathname to  their  file  argument,  unless  the  current
       pathname  is not set, in which case they set the current pathname to their file arguments.
       The alternate pathname was not historically  set  by  the  :source  command.  POSIX.1‐2008
       requires  conformance  to  historical practice.  Implementations adding commands that take
       filenames as arguments are encouraged to set the alternate pathname as described here.

       Historically, ex and vi read the .exrc file in the $HOME directory twice,  if  the  editor
       was executed in the $HOME directory. POSIX.1‐2008 prohibits this behavior.

       Historically,  the 4 BSD ex and vi read the $HOME and local .exrc files if they were owned
       by the real ID of the  user,  or  the  sourceany  option  was  set,  regardless  of  other
       considerations.  This  was  a  security  problem because it is possible to put normal UNIX
       system commands inside a .exrc file. POSIX.1‐2008 does not specify the  sourceany  option,
       and historical implementations are encouraged to delete it.

       The .exrc files must be owned by the real ID of the user, and not writable by anyone other
       than the owner. The appropriate privileges  exception  is  intended  to  permit  users  to
       acquire special privileges, but continue to use the .exrc files in their home directories.

       System V Release 3.2 and later vi implementations added the option [no]exrc.  The behavior
       is that local .exrc files are read-only if the exrc option is set.  The  default  for  the
       exrc  option was off, so by default, local .exrc files were not read. The problem this was
       intended to solve was that System V permitted users to give away files,  so  there  is  no
       possible  ownership  or writeability test to ensure that the file is safe. This is still a
       security problem on systems where  users  can  give  away  files,  but  there  is  nothing
       additional  that  POSIX.1‐2008 can do. The implementation-defined exception is intended to
       permit groups to have local .exrc files that are shared by users, by creating pseudo-users
       to own the shared files.

       POSIX.1‐2008  does  not  mention system-wide ex and vi start-up files. While they exist in
       several implementations of ex  and  vi,  they  are  not  present  in  any  implementations
       considered  historical  practice  by  POSIX.1‐2008.  Implementations  that have such files
       should use them only if they are owned by the real user ID or  an  appropriate  user  (for
       example,  root  on UNIX systems) and if they are not writable by any user other than their
       owner. System-wide start-up files should be read before the EXINIT variable,  $HOME/.exrc,
       or local .exrc files are evaluated.

       Historically,  any  ex  command could be entered in the EXINIT variable or the .exrc file,
       although ones requiring that the edit buffer  already  contain  lines  of  text  generally
       caused  historical implementations of the editor to drop core.  POSIX.1‐2008 requires that
       any ex command be permitted in the EXINIT variable and  .exrc  files,  for  simplicity  of
       specification  and  consistency,  although  many  of  them  will obviously fail under many
       circumstances.

       The initialization of the contents of the edit buffer uses the phrase ``the  effect  shall
       be''  with  regard  to  various ex commands. The intent of this phrase is that edit buffer
       contents loaded during the initialization phase not be lost; that  is,  loading  the  edit
       buffer  should  fail  if  the  .exrc  file  read  in  the  contents  of a file and did not
       subsequently write the edit buffer. An additional intent of this phrase is to specify that
       the initial current line and column is set as specified for the individual ex commands.

       Historically,  the -t option behaved as if the tag search were a +command; that is, it was
       executed from the last line of the file specified by the tag. This resulted in the  search
       failing  if  the pattern was a forward search pattern and the wrapscan edit option was not
       set. POSIX.1‐2008 does not permit this behavior, requiring that the  search  for  the  tag
       pattern  be  performed on the entire file, and, if not found, that the current line be set
       to a more reasonable location in the file.

       Historically, the empty edit buffer presented for editing when a file was not specified by
       the  user  was  unnamed.  This  is permitted by POSIX.1‐2008; however, implementations are
       encouraged to provide users a temporary filename for this buffer because it  permits  them
       the use of ex commands that use the current pathname during temporary edit sessions.

       Historically,  the file specified using the -t option was not part of the current argument
       list. This practice is permitted by POSIX.1‐2008; however, implementations are  encouraged
       to include its name in the current argument list for consistency.

       Historically,  the  -c command was generally not executed until a file that already exists
       was edited. POSIX.1‐2008 requires conformance to this historical practice.  Commands  that
       could  cause  the  -c  command to be executed include the ex commands edit, next, recover,
       rewind, and tag, and the vi commands <control>‐^ and <control>‐].  Historically, reading a
       file into an edit buffer did not cause the -c command to be executed (even though it might
       set the current pathname) with the exception that it  did  cause  the  -c  command  to  be
       executed  if: the editor was in ex mode, the edit buffer had no current pathname, the edit
       buffer was empty, and no read  commands  had  yet  been  attempted.  For  consistency  and
       simplicity of specification, POSIX.1‐2008 does not permit this behavior.

       Historically, the -r option was the same as a normal edit session if there was no recovery
       information available for the file. This allowed users to enter:

           vi -r *.c

       and recover whatever  files  were  recoverable.  In  some  implementations,  recovery  was
       attempted  only  on  the  first file named, and the file was not entered into the argument
       list; in others, recovery was attempted for each file named. In addition, some  historical
       implementations  ignored  -r  if  -t  was  specified  or did not support command line file
       arguments  with  the  -t  option.  For  consistency  and  simplicity   of   specification,
       POSIX.1‐2008  disallows  these  special cases, and requires that recovery be attempted the
       first time each file is edited.

       Historically, vi initialized the ` and ' marks, but ex did not. This  meant  that  if  the
       first  command  in ex mode was visual or if an ex command was executed first (for example,
       vi +10 file), vi was entered without the marks being  initialized.  Because  the  standard
       developers  believed  the marks to be generally useful, and for consistency and simplicity
       of specification, POSIX.1‐2008 requires that they always be  initialized  if  in  open  or
       visual  mode, or if in ex mode and the edit buffer is not empty. Not initializing it in ex
       mode if the edit buffer is empty is historical  practice;  however,  it  has  always  been
       possible  to  set  (and  use)  marks  in  empty  edit buffers in open and visual mode edit
       sessions.

   Addressing
       Historically, ex and vi accepted the additional addressing forms '\/' and '\?'.  They were
       equivalent  to  "//" and "??", respectively. They are not required by POSIX.1‐2008, mostly
       because nobody can remember whether they ever did anything different historically.

       Historically, ex and vi permitted an address of zero for several commands,  and  permitted
       the  %  address  in empty files for others. For consistency, POSIX.1‐2008 requires support
       for the former in the few commands where it makes sense, and disallows  it  otherwise.  In
       addition,  because  POSIX.1‐2008  requires  that % be logically equivalent to "1,$", it is
       also supported where it makes sense and disallowed otherwise.

       Historically, the % address could not be followed by further  addresses.  For  consistency
       and  simplicity  of  specification,  POSIX.1‐2008  requires  that  additional addresses be
       supported.

       All of the following are valid addresses:

       +++       Three lines after the current line.

       /re/-     One line before the next occurrence of re.

       -2        Two lines before the current line.

       3 ---- 2  Line one (note intermediate negative address).

       1 2 3     Line six.

       Any number of addresses can  be  provided  to  commands  taking  addresses;  for  example,
       "1,2,3,4,5p"  prints  lines 4 and 5, because two is the greatest valid number of addresses
       accepted by the print command.  This,  in  combination  with  the  <semicolon>  delimiter,
       permits  users  to create commands based on ordered patterns in the file. For example, the
       command 3;/foo/;+2print will display the first line after line 3 that contains the pattern
       foo,  plus  the  next  two  lines. Note that the address 3; must be evaluated before being
       discarded because the search origin for the /foo/ command depends on this.

       Historically, values could be added to addresses by  including  them  after  one  or  more
       <blank>  characters;  for  example, 3 - 5p wrote the seventh line of the file, and /foo/ 5
       was the same as /foo/+5.  However, only absolute  values  could  be  added;  for  example,
       5 /foo/  was  an error. POSIX.1‐2008 requires conformance to historical practice.  Address
       offsets are separately  specified  from  addresses  because  they  could  historically  be
       provided to visual mode search commands.

       Historically,  any  missing  addresses  defaulted  to  the current line. This was true for
       leading and trailing <comma>-delimited addresses, and for  trailing  <semicolon>-delimited
       addresses.  For consistency, POSIX.1‐2008 requires it for leading <semicolon> addresses as
       well.

       Historically, ex and vi accepted the '^' character as both an address and as a flag offset
       for  commands.  In both cases it was identical to the '-' character. POSIX.1‐2008 does not
       require or prohibit this behavior.

       Historically, the enhancements to basic regular expressions could be used  in  addressing;
       for  example,  '~',  '\<',  and  '\>'.   POSIX.1‐2008  requires  conformance to historical
       practice; that  is,  that  regular  expression  usage  be  consistent,  and  that  regular
       expression enhancements be supported wherever regular expressions are used.

   Command Line Parsing in ex
       Historical ex command parsing was even more complex than that described here. POSIX.1‐2008
       requires the subset of the command parsing  that  the  standard  developers  believed  was
       documented  and  that users could reasonably be expected to use in a portable fashion, and
       that was historically consistent between implementations. (The discarded functionality  is
       obscure,  at  best.)   Historical  implementations will require changes in order to comply
       with POSIX.1‐2008; however, users are not expected to notice any of these  changes.   Most
       of the complexity in ex parsing is to handle three special termination cases:

        1. The !, global, v, and the filter versions of the read and write commands are delimited
           by <newline> characters (they can contain <vertical-line> characters that are  usually
           shell pipes).

        2. The  ex, edit, next, and visual in open and visual mode commands all take ex commands,
           optionally containing <vertical-line> characters, as their first arguments.

        3. The s command takes  a  regular  expression  as  its  first  argument,  and  uses  the
           delimiting characters to delimit the command.

       Historically,  <vertical-line>  characters in the +command argument of the ex, edit, next,
       vi, and visual commands, and in the pattern and replacement parts of the  s  command,  did
       not  delimit  the  command, and in the filter cases for read and write, and the !, global,
       and v commands, they did not delimit the  command  at  all.  For  example,  the  following
       commands are all valid:

           :edit +25 | s/abc/ABC/ file.c
           :s/ | /PIPE/
           :read !spell % | columnate
           :global/pattern/p | l
           :s/a/b/ | s/c/d | set

       Historically,  empty  or <blank> filled lines in .exrc files and sourced files (as well as
       EXINIT variables and ex command scripts) were treated as default commands; that is,  print
       commands.  POSIX.1‐2008  specifically  requires  that  they be ignored when encountered in
       .exrc and sourced files to eliminate a common source of new user error.

       Historically, ex commands with multiple adjacent  (or  <blank>-separated)  vertical  lines
       were  handled  oddly  when  executed from ex mode. For example, the command ||| <carriage-
       return>, when the cursor was on line 1, displayed lines 2, 3,  and  5  of  the  file.   In
       addition,  the  command  | would only display the line after the next line, instead of the
       next two lines. The former worked more logically when executed from vi mode, and displayed
       lines  2,  3,  and  4.  POSIX.1‐2008  requires  the vi behavior; that is, a single default
       command and line number increment for  each  command  separator,  and  trailing  <newline>
       characters after <vertical-line> separators are discarded.

       Historically,  ex  permitted  a  single  extra <colon> as a leading command character; for
       example, :g/pattern/:p was a valid command. POSIX.1‐2008 generalizes this to require  that
       any number of leading <colon> characters be stripped.

       Historically,  any  prefix  of  the  delete  command could be followed without intervening
       <blank> characters by a flag character because in the command d p, p is interpreted as the
       buffer p.  POSIX.1‐2008 requires conformance to historical practice.

       Historically, the k command could be followed by the mark name without intervening <blank>
       characters. POSIX.1‐2008 requires conformance to historical practice.

       Historically, the s command could be immediately followed by flag and  option  characters;
       for  example, s/e/E/|s|sgc3p was a valid command. However, flag characters could not stand
       alone; for example, the commands sp and s l would fail, while the  command  sgp  and  s gl
       would  succeed. (Obviously, the '#' flag character was used as a delimiter character if it
       followed the command.) Another issue was  that  option  characters  had  to  precede  flag
       characters  even  when  the command was fully specified; for example, the command s/e/E/pg
       would fail, while the command s/e/E/gp would succeed. POSIX.1‐2008 requires conformance to
       historical practice.

       Historically,  the  first  command name that had a prefix matching the input from the user
       was the executed command; for example, ve, ver, and vers all executed the version command.
       Commands  were  in  a  specific  order, however, so that a matched append, not abbreviate.
       POSIX.1‐2008 requires conformance to  historical  practice.  The  restriction  on  command
       search order for implementations with extensions is to avoid the addition of commands such
       that the historical prefixes would fail to work portably.

       Historical implementations of ex and vi did not correctly  handle  multiple  ex  commands,
       separated by <vertical-line> characters, that entered or exited visual mode or the editor.
       Because implementations of vi exist that do not exhibit this  failure  mode,  POSIX.1‐2008
       does not permit it.

       The  requirement  that  alphabetic  command  names  consist  of  all  following alphabetic
       characters up to the next non-alphabetic character means  that  alphabetic  command  names
       must  be separated from their arguments by one or more non-alphabetic characters, normally
       a <blank> or '!'  character, except as specified for the exceptions, the delete, k, and  s
       commands.

       Historically,  the  repeated execution of the ex default print commands (<control>‐D, eof,
       <newline>, <carriage-return>) erased any prompting character and displayed the next  lines
       without scrolling the terminal; that is, immediately below any previously displayed lines.
       This provided a cleaner presentation of the lines in the file for the  user.  POSIX.1‐2008
       does  not  require this behavior because it may be impossible in some situations; however,
       implementations are strongly encouraged to provide this semantic if possible.

       Historically, it was possible to change files in the middle of a  command,  and  have  the
       rest of the command executed in the new file; for example:

           :edit +25 file.c | s/abc/ABC/ | 1

       was  a  valid  command,  and  the  substitution  was  attempted  in the newly edited file.
       POSIX.1‐2008 requires conformance to  historical  practice.  The  following  commands  are
       examples that exercise the ex parser:

           echo 'foo | bar' > file1; echo 'foo/bar' > file2;
           vi
           :edit +1 | s/|/PIPE/ | w file1 | e file2 | 1 | s/\//SLASH/ | wq

       Historically,  there was no protection in editor implementations to avoid ex global, v, @,
       or * commands changing edit buffers during execution of their associated commands. Because
       this   would  almost  invariably  result  in  catastrophic  failure  of  the  editor,  and
       implementations exist that do exhibit these problems, POSIX.1‐2008 requires that  changing
       the  edit  buffer during a global or v command, or during a @ or * command for which there
       will be more than a single execution, be an  error.  Implementations  supporting  multiple
       edit  buffers  simultaneously  are  strongly  encouraged  to  apply  the same semantics to
       switching between buffers as well.

       The ex command quoting required by POSIX.1‐2008 is a superset of the quoting in historical
       implementations  of  the editor. For example, it was not historically possible to escape a
       <blank> in a filename; for example, :edit foo\\\ bar would report that too many  filenames
       had  been  entered  for the edit command, and there was no method of escaping a <blank> in
       the first argument of an edit, ex, next, or visual command at  all.  POSIX.1‐2008  extends
       historical  practice,  requiring  that  quoting  behavior be made consistent across all ex
       commands, except  for  the  map,  unmap,  abbreviate,  and  unabbreviate  commands,  which
       historically  used  <control>‐V  instead  of <backslash> characters for quoting. For those
       four commands, POSIX.1‐2008 requires conformance to historical practice.

       Backslash quoting in ex is non-intuitive.  <backslash>-escapes  are  ignored  unless  they
       escape  a  special  character;  for  example, when performing file argument expansion, the
       string "\\%" is equivalent to '\%', not "\<current pathname>".  This can be confusing  for
       users  because <backslash> is usually one of the characters that causes shell expansion to
       be performed, and  therefore  shell  quoting  rules  must  be  taken  into  consideration.
       Generally,  quoting characters are only considered if they escape a special character, and
       a quoting character must be provided for each layer of parsing for which the character  is
       special.  As another example, only a single <backslash> is necessary for the '\l' sequence
       in substitute replacement patterns, because the  character  'l'  is  not  special  to  any
       parsing layer above it.

       <control>‐V  quoting  in  ex  is  slightly  different  from backslash quoting. In the four
       commands where <control>‐V quoting applies (abbreviate, unabbreviate, map, and unmap), any
       character  may be escaped by a <control>‐V whether it would have a special meaning or not.
       POSIX.1‐2008 requires conformance to historical practice.

       Historical implementations of the editor  did  not  require  delimiters  within  character
       classes  to  be  escaped;  for example, the command :s/[/]// on the string "xxx/yyy" would
       delete the '/' from the  string.  POSIX.1‐2008  disallows  this  historical  practice  for
       consistency  and  because  it  places  a large burden on implementations by requiring that
       knowledge of regular expressions be built into the editor parser.

       Historically, quoting <newline> characters in ex commands was handled  inconsistently.  In
       most  cases,  the  <newline>  character  always  terminated the command, regardless of any
       preceding escape character,  because  <backslash>  characters  did  not  escape  <newline>
       characters  for  most  ex  commands.  However,  some ex commands (for example, s, map, and
       abbreviation) permitted <newline> characters to be escaped (although in the  case  of  map
       and  abbreviation, <control>‐V characters escaped them instead of <backslash> characters).
       This was true in not only the command line, but also .exrc and sourced files. For example,
       the command:

           map = foo<control-V><newline>bar

       would succeed, although it was sometimes difficult to get the <control>‐V and the inserted
       <newline> passed to the ex  parser.  For  consistency  and  simplicity  of  specification,
       POSIX.1‐2008 requires that it be possible to escape <newline> characters in ex commands at
       all times, using <backslash> characters  for  most  ex  commands,  and  using  <control>‐V
       characters   for   the   map   and   abbreviation   commands.  For  example,  the  command
       print<newline>list is required to be parsed  as  the  single  command  print<newline>list.
       While  this differs from historical practice, POSIX.1‐2008 developers believed it unlikely
       that any script or user depended on the historical behavior.

       Historically, an error in a command specified using the -c option did not cause  the  rest
       of  the  -c  commands  to  be  discarded. POSIX.1‐2008 disallows this for consistency with
       mapped keys, the @, global, source, and v commands, the EXINIT environment  variable,  and
       the .exrc files.

   Input Editing in ex
       One  of  the  common  uses  of  the historical ex editor is over slow network connections.
       Editors that run in canonical mode can require far less traffic to and from, and far  less
       processing  on,  the host machine, as well as more easily supporting block-mode terminals.
       For these reasons, POSIX.1‐2008 requires that ex be implemented using canonical mode input
       processing, as was done historically.

       POSIX.1‐2008 does not require the historical 4 BSD input editing characters ``word erase''
       or ``literal next''. For this reason, it is  unspecified  how  they  are  handled  by  ex,
       although  they  must have the required effect. Implementations that resolve them after the
       line has been ended using a <newline> or <control>‐M character, and  implementations  that
       rely  on  the underlying system terminal support for this processing, are both conforming.
       Implementations are strongly urged to use the underlying system functionality, if  at  all
       possible, for compatibility with other system text input interfaces.

       Historically,  when  the  eof  character  was  used to decrement the autoindent level, the
       cursor moved to display the new end of the autoindent characters, but  did  not  move  the
       cursor  to  a  new  line,  nor  did  it  erase  the  <control>‐D  character from the line.
       POSIX.1‐2008 does not specify that the cursor remain on the same line or that the rest  of
       the  line  is erased; however, implementations are strongly encouraged to provide the best
       possible user interface; that is, the cursor should remain  on  the  same  line,  and  any
       <control>‐D character on the line should be erased.

       POSIX.1‐2008  does  not  require the historical 4 BSD input editing character ``reprint'',
       traditionally <control>‐R, which redisplayed the current input from  the  user.  For  this
       reason,  and  because  the  functionality  cannot  be  implemented after the line has been
       terminated by the user, POSIX.1‐2008  makes  no  requirements  about  this  functionality.
       Implementations  are  strongly  urged  to make this historical functionality available, if
       possible.

       Historically, <control>‐Q did not perform a literal next function in ex, as it did in  vi.
       POSIX.1‐2008  requires  conformance to historical practice to avoid breaking historical ex
       scripts and .exrc files.

   eof
       Whether the eof character immediately modifies the autoindent characters in the prompt  is
       left  unspecified  so  that implementations can conform in the presence of systems that do
       not support this functionality. Implementations are encouraged  to  modify  the  line  and
       redisplay it immediately, if possible.

       The  specification  of  the handling of the eof character differs from historical practice
       only in that eof characters are not discarded if they follow normal characters in the text
       input. Historically, they were always discarded.

   Command Descriptions in ex
       Historically,  several commands (for example, global, v, visual, s, write, wq, yank, !, <,
       >, &, and ~) were executable in empty files (that is, the default address(es) were 0),  or
       permitted  explicit addresses of 0 (for example, 0 was a valid address, or 0,0 was a valid
       range). Addresses of 0, or command execution  in  an  empty  file,  make  sense  only  for
       commands that add new text to the edit buffer or write commands (because users may wish to
       write empty files). POSIX.1‐2008 requires this behavior for such commands and disallows it
       otherwise, for consistency and simplicity of specification.

       A  count  to  an ex command has been historically corrected to be no greater than the last
       line in a file; for example, in a five-line file, the command 1,6print would fail, but the
       command 1print300 would succeed. POSIX.1‐2008 requires conformance to historical practice.

       Historically,  the  use  of  flags  in  ex  commands  could be obscure. General historical
       practice was as described  by  POSIX.1‐2008,  but  there  were  some  special  cases.  For
       instance,  the  list,  number,  and  print  commands ignored trailing address offsets; for
       example, 3p +++# would display line 3, and 3 would be the current line after the execution
       of  the  command.  The  open and visual commands ignored both the trailing offsets and the
       trailing flags.  Also, flags specified to the open and visual  commands  interacted  badly
       with  the  list  edit  option,  and  setting  and then unsetting it during the open/visual
       session would cause vi to stop displaying lines in the specified format.  For  consistency
       and  simplicity  of specification, POSIX.1‐2008 does not permit any of these exceptions to
       the general rule.

       POSIX.1‐2008 uses the word copy in several places when discussing  buffers.  This  is  not
       intended to imply implementation.

       Historically,  ex  users  could  not specify numeric buffers because of the ambiguity this
       would cause; for example, in the command 3 delete 2, it is unclear whether 2 is  a  buffer
       name or a count.  POSIX.1‐2008 requires conformance to historical practice by default, but
       does not preclude extensions.

       Historically, the contents of the unnamed buffer were frequently discarded after  commands
       that  did  not  explicitly  affect  it; for example, when using the edit command to switch
       files. For consistency and simplicity of specification, POSIX.1‐2008 does not permit  this
       behavior.

       The  ex utility did not historically have access to the numeric buffers, and, furthermore,
       deleting lines in ex did not modify their contents. For example, if, after doing a  delete
       in  vi,  the  user  switched  to ex, did another delete, and then switched back to vi, the
       contents of the numeric buffers would not have changed. POSIX.1‐2008 requires  conformance
       to  historical  practice.  Numeric  buffers  are  described  in the ex utility in order to
       confine the description of buffers to a single location in POSIX.1‐2008.

       The metacharacters that  trigger  shell  expansion  in  file  arguments  match  historical
       practice, as does the method for doing shell expansion. Implementations wishing to provide
       users with the flexibility to alter the set of metacharacters are encouraged to provide  a
       shellmeta string edit option.

       Historically,  ex  commands executed from vi refreshed the screen when it did not strictly
       need to do so; for example, :!date > /dev/null does not require a screen  refresh  because
       the  output  of  the  UNIX  date  command  requires  only  a  single  line  of the screen.
       POSIX.1‐2008 requires that the screen be refreshed if it has been overwritten,  but  makes
       no   requirements   as   to   how   an  implementation  should  make  that  determination.
       Implementations may prompt and refresh the screen regardless.

   Abbreviate
       Historical practice was that characters that were  entered  as  part  of  an  abbreviation
       replacement   were   subject  to  map  expansions,  the  showmatch  edit  option,  further
       abbreviation expansions, and so on; that is, they were logically pushed onto the  terminal
       input  queue,  and  were  not  a  simple replacement. POSIX.1‐2008 requires conformance to
       historical practice.  Historical practice was that whenever a non-word character (that had
       not  been escaped by a <control>‐V) was entered after a word character, vi would check for
       abbreviations. The check was based on the type of the character entered  before  the  word
       character  of  the  word/non-word pair that triggered the check. The word character of the
       word/non-word pair that triggered the check and all characters entered before the  trigger
       pair  that  were  of  that  type were included in the check, with the exception of <blank>
       characters, which always delimited the abbreviation.

       This means that, for the abbreviation to work, the lhs must end  with  a  word  character,
       there  can  be  no transitions from word to non-word characters (or vice versa) other than
       between the last and next-to-last characters in the lhs,  and  there  can  be  no  <blank>
       characters  in  the  lhs.   In  addition,  because of the historical quoting rules, it was
       impossible to enter a literal <control>‐V in the lhs.  POSIX.1‐2008  requires  conformance
       to historical practice. Historical implementations did not inform users when abbreviations
       that could never be used were entered; implementations are strongly encouraged to do so.

       For example, the following abbreviations will work:

           :ab (p  REPLACE
           :ab p   REPLACE
           :ab ((p REPLACE

       The following abbreviations will not work:

           :ab (   REPLACE
           :ab (pp REPLACE

       Historical practice  is  that  words  on  the  vi  colon  command  line  were  subject  to
       abbreviation expansion, including the arguments to the abbrev (and more interestingly) the
       unabbrev command. Because there are implementations that do not do abbreviation  expansion
       for  the  first  argument  to  those  commands,  this  is  permitted, but not required, by
       POSIX.1‐2008. However, the following sequence:

           :ab foo bar
           :ab foo baz

       resulted in the addition of an abbreviation of "baz" for the string  "bar"  in  historical
       ex/vi, and the sequence:

           :ab foo1 bar
           :ab foo2 bar
           :unabbreviate foo2

       deleted  the  abbreviation  "foo1",  not  "foo2".   These  behaviors  are not permitted by
       POSIX.1‐2008 because they clearly violate the expectations of the user.

       It was historical practice that <control>‐V, not <backslash>, characters be interpreted as
       escaping   subsequent   characters   in  the  abbreviate  command.  POSIX.1‐2008  requires
       conformance to historical practice; however, it  should  be  noted  that  an  abbreviation
       containing a <blank> will never work.

   Append
       Historically,  any  text  following  a  <vertical-line> command separator after an append,
       change, or insert command became part of the insert text. For example, in the command:

           :g/pattern/append|stuff1

       a line containing the text "stuff1" would be appended to each line  matching  pattern.  It
       was also historically valid to enter:

           :append|stuff1
           stuff2
           .

       and  the  text on the ex command line would be appended along with the text inserted after
       it.  There was an historical bug, however, that the user  had  to  enter  two  terminating
       lines  (the  '.'   lines) to terminate text input mode in this case. POSIX.1‐2008 requires
       conformance to historical  practice,  but  disallows  the  historical  need  for  multiple
       terminating lines.

   Change
       See the RATIONALE for the append command. Historical practice for cursor positioning after
       the change command when no text is input, is as described in  POSIX.1‐2008.  However,  one
       System  V implementation is known to have been modified such that the cursor is positioned
       on the first address specified, and not on the line before the first address. POSIX.1‐2008
       disallows this modification for consistency.

       Historically,  the  change  command  did  not  support  buffer  arguments,  although  some
       implementations allow the specification of an optional buffer. This  behavior  is  neither
       required nor disallowed by POSIX.1‐2008.

   Change Directory
       A common extension in ex implementations is to use the elements of a cdpath edit option as
       prefix directories for path arguments to chdir that are relative pathnames and that do not
       have  '.'   or  ".."  as  their  first  component.  Elements in the cdpath edit option are
       <colon>-separated.  The initial value of the cdpath edit option is the value of the  shell
       CDPATH environment variable. This feature was not included in POSIX.1‐2008 because it does
       not exist in any of the implementations considered historical practice.

   Copy
       Historical implementations of ex permitted copies to lines inside of the specified  range;
       for  example,  :2,5copy3  was  a  valid  command.  POSIX.1‐2008  requires  conformance  to
       historical practice.

   Delete
       POSIX.1‐2008 requires support for the historical parsing of a delete command  followed  by
       flags, without any intervening <blank> characters. For example:

       1dp     Deletes the first line and prints the line that was second.

       1delep  As for 1dp.

       1d      Deletes the first line, saving it in buffer p.

       1d p1l  (Pee-one-ell.) Deletes the first line, saving it in buffer p, and listing the line
               that was second.

   Edit
       Historically, any ex command could be entered as a +command argument to the edit  command,
       although  some  (for  example,  insert  and  append)  were  known  to  confuse  historical
       implementations. For consistency and simplicity of  specification,  POSIX.1‐2008  requires
       that any command be supported as an argument to the edit command.

       Historically, the command argument was executed with the current line set to the last line
       of the file, regardless of whether the edit command was executed from visual mode or  not.
       POSIX.1‐2008 requires conformance to historical practice.

       Historically,  the  +command  specified to the edit and next commands was delimited by the
       first <blank>, and there was no way to quote them. For consistency, POSIX.1‐2008  requires
       that the usual ex backslash quoting be provided.

       Historically,  specifying the +command argument to the edit command required a filename to
       be specified as well; for example, :edit +100  would  always  fail.  For  consistency  and
       simplicity  of  specification,  POSIX.1‐2008  does  not permit this usage to fail for that
       reason.

       Historically, only the cursor position of the last  file  edited  was  remembered  by  the
       editor.  POSIX.1‐2008  requires  that  this  be  supported;  however,  implementations are
       permitted to remember and restore the cursor position for any file previously edited.

   File
       Historical versions of the ex editor file command displayed a current line and  number  of
       lines  in  the  edit buffer of 0 when the file was empty, while the vi <control>‐G command
       displayed a current line and number of  lines  in  the  edit  buffer  of  1  in  the  same
       situation. POSIX.1‐2008 does not permit this discrepancy, instead requiring that a message
       be displayed indicating that the file is empty.

   Global
       The  two-pass  operation  of  the  global  and  v  commands  is  not  intended  to   imply
       implementation, only the required result of the operation.

       The  current  line  and  column  are set as specified for the individual ex commands. This
       requirement is cumulative; that is, the current line and column must track across all  the
       commands executed by the global or v commands.

   Insert
       See the RATIONALE for the append command.

       Historically, insert could not be used with an address of zero; that is, not when the edit
       buffer was empty. POSIX.1‐2008 requires that this command  behave  consistently  with  the
       append command.

   Join
       The  action  of the join command in relation to the special characters is only defined for
       the POSIX locale because the correct amount of white  space  after  a  period  varies;  in
       Japanese none is required, in French only a single space, and so on.

   List
       The  historical  output  of  the  list  command  was  potentially  ambiguous. The standard
       developers believed correcting this to be  more  important  than  adhering  to  historical
       practice, and POSIX.1‐2008 requires unambiguous output.

   Map
       Historically,  command  mode  maps  only  applied  to  command  names; for example, if the
       character 'x' was mapped to 'y', the command fx searched for the 'x'  character,  not  the
       'y'  character. POSIX.1‐2008 requires this behavior. Historically, entering <control>‐V as
       the first character of a vi command was an error. Several  implementations  have  extended
       the  semantics  of vi such that <control>‐V means that the subsequent command character is
       not mapped. This is permitted,  but  not  required,  by  POSIX.1‐2008.  Regardless,  using
       <control>‐V to escape the second or later character in a sequence of characters that might
       match a map command, or any character in text input  mode,  is  historical  practice,  and
       stops  the  entered  keys  from  matching  a  map.  POSIX.1‐2008  requires  conformance to
       historical practice.

       Historical implementations permitted digits to be used as a  map  command  lhs,  but  then
       ignored the map. POSIX.1‐2008 requires that the mapped digits not be ignored.

       The  historical  implementation  of  the map command did not permit map commands that were
       more than a single character in length if the first character was printable. This behavior
       is permitted, but not required, by POSIX.1‐2008.

       Historically, mapped characters were remapped unless the remap edit option was not set, or
       the prefix of the mapped characters matched the mapping characters; for  example,  in  the
       map:

           :map ab abcd

       the  characters  "ab"  were used as is and were not remapped, but the characters "cd" were
       mapped if appropriate. This can  cause  infinite  loops  in  the  vi  mapping  mechanisms.
       POSIX.1‐2008  requires  conformance  to  historical  practice,  and  that  such  loops  be
       interruptible.

       Text input maps had the same problems with expanding the lhs for the ex map!   and  unmap!
       command  as  did the ex abbreviate and unabbreviate commands. See the RATIONALE for the ex
       abbreviate command. POSIX.1‐2008 requires similar modification of some historical practice
       for the map and unmap commands, as described for the abbreviate and unabbreviate commands.

       Historically,  maps  that  were subsets of other maps behaved differently depending on the
       order in which they were defined.  For example:

           :map! ab     short
           :map! abc    long

       would always translate the  characters  "ab"  to  "short",  regardless  of  how  fast  the
       characters "abc" were entered. If the entry order was reversed:

           :map! abc    long
           :map! ab     short

       the  characters  "ab"  would  cause  the  editor  to pause, waiting for the completing 'c'
       character, and the characters might never be  mapped  to  "short".   For  consistency  and
       simplicity  of specification, POSIX.1‐2008 requires that the shortest match be used at all
       times.

       The length of time the editor spends waiting for the characters to  complete  the  lhs  is
       unspecified because the timing capabilities of systems are often inexact and variable, and
       it may depend on other factors such as the speed of the connection.  The  time  should  be
       long  enough for the user to be able to complete the sequence, but not long enough for the
       user to have to wait. Some implementations of  vi  have  added  a  keytime  option,  which
       permits  users  to  set  the  number  of  0,1  seconds the editor waits for the completing
       characters. Because mapped terminal function and cursor keys tend to start with  an  <ESC>
       character,  and  <ESC>  is  the  key  ending  vi text input mode, maps starting with <ESC>
       characters are generally exempted from  this  timeout  period,  or,  at  least  timed  out
       differently.

   Mark
       Historically,  users  were  able  to  set  the  ``previous  context'' marks explicitly. In
       addition, the ex commands '' and '` and the vi commands '', ``, `', and '` all referred to
       the  same  mark. In addition, the previous context marks were not set if the command, with
       which  the  address  setting  the  mark  was  associated,  failed.  POSIX.1‐2008  requires
       conformance  to  historical practice. Historically, if marked lines were deleted, the mark
       was also deleted, but would reappear if  the  change  was  undone.  POSIX.1‐2008  requires
       conformance to historical practice.

       The  description  of  the  special  events  that  set the ` and ' marks matches historical
       practice. For example, historically the command /a/,/b/ did not set the ` and ' marks, but
       the command /a/,/b/delete did.

   Next
       Historically,  any ex command could be entered as a +command argument to the next command,
       although  some  (for  example,  insert  and  append)  were  known  to  confuse  historical
       implementations. POSIX.1‐2008 requires that any command be permitted and that it behave as
       specified. The next command can accept more than one file, so usage such as:

           next `ls [abc] `

       is valid; it need not be valid for the edit or read commands, for  example,  because  they
       expect only one filename.

       Historically,  the  next  command  behaved differently from the :rewind command in that it
       ignored the force flag if the autowrite flag was set. For consistency,  POSIX.1‐2008  does
       not permit this behavior.

       Historically,  the next command positioned the cursor as if the file had never been edited
       before, regardless. POSIX.1‐2008 does not permit this behavior, for consistency  with  the
       edit command.

       Implementations  wanting  to  provide  a  counterpart  to the next command that edited the
       previous file have used the command prev[ious], which takes no file argument. POSIX.1‐2008
       does not require this command.

   Open
       Historically,  the  open  command  would  fail  if  the  open  edit  option  was  not set.
       POSIX.1‐2008 does not mention the open edit option and does  not  require  this  behavior.
       Some historical implementations do not permit entering open mode from open or visual mode,
       only from ex mode. For consistency, POSIX.1‐2008 does not permit this behavior.

       Historically, entering open mode from the command line (that is,  vi  +open)  resulted  in
       anomalous  behaviors;  for  example,  the  ex  file  and  set commands, and the vi command
       <control>‐G did not work. For consistency, POSIX.1‐2008 does not permit this behavior.

       Historically, the open command only permitted '/' characters to  be  used  as  the  search
       pattern  delimiter. For consistency, POSIX.1‐2008 requires that the search delimiters used
       by the s, global, and v commands be accepted as well.

   Preserve
       The preserve command does not historically cause the file to be considered unmodified  for
       the  purposes  of  future  commands  that  may  exit  the  editor.  POSIX.1‐2008  requires
       conformance to historical practice.

       Historical documentation stated that mail was not sent  to  the  user  when  preserve  was
       executed;  however,  historical  implementations  did send mail in this case. POSIX.1‐2008
       requires conformance to the historical implementations.

   Print
       The writing of NUL by the print command is not specified as a  special  case  because  the
       standard  developers  did  not want to require ex to support NUL characters. Historically,
       characters were displayed using the ARPA standard mappings, which are as follows:

        1. Printable characters are left alone.

        2. Control characters less than \177 are represented as '^'  followed  by  the  character
           offset  from  the  '@' character in the ASCII map; for example, \007 is represented as
           '^G'.

        3. \177 is represented as '^' followed by '?'.

       The display of characters  having  their  eighth  bit  set  was  less  standard.  Existing
       implementations  use  hex  (0x00),  octal  (\000),  and  a  meta-bit  display. (The latter
       displayed bytes that had their eighth bit set as the two characters "M-" followed  by  the
       seven-bit  display  as  described  above.)  The  latter  probably  has  the  best claim to
       historical practice because it was used for the -v option  of  4  BSD  and  4  BSD-derived
       versions of the cat utility since 1980.

       No specific display format is required by POSIX.1‐2008.

       Explicit  dependence on the ASCII character set has been avoided where possible, hence the
       use of the phrase an ``implementation-defined multi-character sequence'' for  the  display
       of  non-printable  characters in preference to the historical usage of, for instance, "^I"
       for the <tab>.  Implementations are encouraged to conform to historical  practice  in  the
       absence of any strong reason to diverge.

       Historically,  all  ex  commands  beginning  with  the  letter  'p' could be entered using
       capitalized versions of the commands; for example, P[rint], Pre[serve], and Pu[t] were all
       valid  command names. POSIX.1‐2008 permits, but does not require, this historical practice
       because capital forms of the commands are used by some implementations for other purposes.

   Put
       Historically, an ex put command, executed from open or visual mode, was the  same  as  the
       open  or visual mode P command, if the buffer was named and was cut in character mode, and
       the same as the p command if the buffer was named and cut in line  mode.  If  the  unnamed
       buffer  was  the  source  of  the  text, the entire line from which the text was taken was
       usually put, and the buffer was handled as if in line mode, but it  was  possible  to  get
       extremely anomalous behavior. In addition, using the Q command to switch into ex mode, and
       then doing a put often resulted in errors  as  well,  such  as  appending  text  that  was
       unrelated  to  the  (supposed)  contents  of the buffer. For consistency and simplicity of
       specification, POSIX.1‐2008 does not permit these  behaviors.  All  ex  put  commands  are
       required  to  operate  in  line  mode,  and the contents of the buffers are not altered by
       changing the mode of the editor.

   Read
       Historically, an ex read command executed from open or visual mode, executed in  an  empty
       file,  left an empty line as the first line of the file. For consistency and simplicity of
       specification, POSIX.1‐2008 does not permit this behavior.  Historically, a read  in  open
       or visual mode from a program left the cursor at the last line read in, not the first. For
       consistency, POSIX.1‐2008 does not permit this behavior.

       Historical implementations of ex were unable to undo read  commands  that  read  from  the
       output of a program. For consistency, POSIX.1‐2008 does not permit this behavior.

       Historically,  the  ex  and  vi message after a successful read or write command specified
       ``characters'',  not  ``bytes''.  POSIX.1‐2008  requires  that  the  number  of  bytes  be
       displayed,  not  the  number  of  characters,  because  it  may be difficult in multi-byte
       implementations to determine the number of characters read. Implementations are encouraged
       to clarify the message displayed to the user.

       Historically,  reads were not permitted on files other than type regular, except that FIFO
       files could be read (probably only because  they  did  not  exist  when  ex  and  vi  were
       originally  written). Because the historical ex evaluated read!  and read !  equivalently,
       there can be no optional way to  force  the  read.  POSIX.1‐2008  permits,  but  does  not
       require, this behavior.

   Recover
       Some  historical  implementations of the editor permitted users to recover the edit buffer
       contents from a previous edit session, and then exit without  saving  those  contents  (or
       explicitly  discarding them). The intent of POSIX.1‐2008 in requiring that the edit buffer
       be treated as already modified is to prevent this user error.

   Rewind
       Historical implementations supported the rewind command when  the  user  was  editing  the
       first file in the list; that is, the file that the rewind command would edit. POSIX.1‐2008
       requires conformance to historical practice.

   Substitute
       Historically, ex accepted an r option to the s command. The effect of the r option was  to
       use  the  last  regular  expression  used in any command as the pattern, the same as the ~
       command. The r option is not required by POSIX.1‐2008. Historically, the c and  g  options
       were  toggled;  for  example,  the command :s/abc/def/ was the same as s/abc/def/ccccgggg.
       For simplicity of specification, POSIX.1‐2008 does not permit this behavior.

       The tilde command is often used to replace  the  last  search  RE.  For  example,  in  the
       sequence:

           s/red/blue/
           /green
           ~

       the ~ command is equivalent to:

           s/green/blue/

       Historically, ex accepted all of the following forms:

           s/abc/def/
           s/abc/def
           s/abc/
           s/abc

       POSIX.1‐2008 requires conformance to this historical practice.

       The  s  command  presumes  that  the  '^'  character  only occupies a single column in the
       display. Much of the ex and vi specification presumes that the  <space>  only  occupies  a
       single  column  in  the  display.  There are no known character sets for which this is not
       true.

       Historically, the final column position for the substitute commands was based on  previous
       column movements; a search for a pattern followed by a substitution would leave the column
       position unchanged, while a 0 command followed by a substitution would change  the  column
       position  to  the  first  non-<blank>.   For  consistency and simplicity of specification,
       POSIX.1‐2008 requires  that  the  final  column  position  always  be  set  to  the  first
       non-<blank>.

   Set
       Historical  implementations  redisplayed all of the options for each occurrence of the all
       keyword. POSIX.1‐2008 permits, but does not require, this behavior.

   Tag
       No requirement is made as to where ex and vi shall look for the file referenced by the tag
       entry.  Historical practice has been to look for the path found in the tags file, based on
       the current directory. A useful extension found in some implementations is to  look  based
       on  the directory containing the tags file that held the entry, as well. No requirement is
       made as to which reference for the tag in the tags file is used. This  is  deliberate,  in
       order to permit extensions such as multiple entries in a tags file for a tag.

       Because  users often specify many different tags files, some of which need not be relevant
       or exist at any particular time, POSIX.1‐2008 requires that error messages  about  problem
       tags  files  be  displayed only if the requested tag is not found, and then, only once for
       each time that the tag edit option is changed.

       The requirement that the current edit buffer be unmodified is only necessary if  the  file
       indicated  by the tag entry is not the same as the current file (as defined by the current
       pathname). Historically, the file would be reloaded if the filename had changed,  as  well
       as if the filename was different from the current pathname. For consistency and simplicity
       of specification, POSIX.1‐2008 does not permit this behavior, requiring that the  name  be
       the only factor in the decision.

       Historically, vi only searched for tags in the current file from the current cursor to the
       end of the file, and therefore, if the wrapscan option was not set, tags occurring  before
       the  current cursor were not found. POSIX.1‐2008 considers this a bug, and implementations
       are required to search for the first occurrence in the file, regardless.

   Undo
       The undo description deliberately uses the word ``modified''.  The  undo  command  is  not
       intended  to  undo  commands  that  replace the contents of the edit buffer, such as edit,
       next, tag, or recover.

       Cursor positioning after the undo command was inconsistent in the historical vi, sometimes
       attempting  to  restore  the  original cursor position (global, undo, and v commands), and
       sometimes, in the presence of maps, placing the cursor on the last line added  or  changed
       instead  of  the  first.  POSIX.1‐2008  requires a simplified behavior for consistency and
       simplicity of specification.

   Version
       The version command  cannot  be  exactly  specified  since  there  is  no  widely-accepted
       definition of what the version information should contain.  Implementations are encouraged
       to do something reasonably intelligent.

   Write
       Historically, the ex and vi message after a successful read  or  write  command  specified
       ``characters'',  not  ``bytes''.  POSIX.1‐2008  requires  that  the  number  of  bytes  be
       displayed, not the number  of  characters  because  it  may  be  difficult  in  multi-byte
       implementations  to  determine  the  number  of  characters  written.  Implementations are
       encouraged to clarify the message displayed to the user.

       Implementation-defined tests are permitted so that  implementations  can  make  additional
       checks; for example, for locks or file modification times.

       Historically, attempting to append to a nonexistent file caused an error. It has been left
       unspecified in POSIX.1‐2008 to permit implementations to let the write  succeed,  so  that
       the append semantics are similar to those of the historical csh.

       Historical  vi  permitted  empty edit buffers to be written. However, since the way vi got
       around dealing with ``empty'' files was to always have a  line  in  the  edit  buffer,  no
       matter  what, it wrote them as files of a single, empty line. POSIX.1‐2008 does not permit
       this behavior.

       Historically, ex restored standard output and standard error to their values as of when ex
       was  invoked,  before  writes  to programs were performed. This could disturb the terminal
       configuration as well as be a security issue for some  terminals.  POSIX.1‐2008  does  not
       permit  this,  requiring that the program output be captured and displayed as if by the ex
       print command.

   Adjust Window
       Historically, the line count was set to the  value  of  the  scroll  option  if  the  type
       character was end-of-file. This feature was broken on most historical implementations long
       ago, however, and is not documented anywhere. For this reason, POSIX.1‐2008 is  resolutely
       silent.

       Historically,  the  z  command  was <blank>-sensitive and z + and z - did different things
       than z+ and z- because the type could not be distinguished from a flag. (The commands  z .
       and  z =  were historically invalid.) POSIX.1‐2008 requires conformance to this historical
       practice.

       Historically, the z command was further <blank>-sensitive in that the count could  not  be
       <blank>-delimited;  for example, the commands z= 5 and z- 5 were also invalid. Because the
       count is not ambiguous with respect to either the type character or the flags, this is not
       permitted by POSIX.1‐2008.

   Escape
       Historically,  ex  filter  commands only read the standard output of the commands, letting
       standard error appear on the terminal  as  usual.  The  vi  utility,  however,  read  both
       standard  output and standard error. POSIX.1‐2008 requires the latter behavior for both ex
       and vi, for consistency.

   Shift Left and Shift Right
       Historically, it was possible to add shift  characters  to  increase  the  effect  of  the
       command;  for  example,  <<< outdented (or >>> indented) the lines 3 levels of indentation
       instead of the default 1.  POSIX.1‐2008 requires conformance to historical practice.

   <control>‐D
       Historically, the <control>‐D command erased  the  prompt,  providing  the  user  with  an
       unbroken presentation of lines from the edit buffer. This is not required by POSIX.1‐2008;
       implementations are encouraged to provide it if possible.  Historically,  the  <control>‐D
       command took, and then ignored, a count.  POSIX.1‐2008 does not permit this behavior.

   Write Line Number
       Historically, the ex = command, when executed in ex mode in an empty edit buffer, reported
       0, and  from  open  or  visual  mode,  reported  1.  For  consistency  and  simplicity  of
       specification, POSIX.1‐2008 does not permit this behavior.

   Execute
       Historically,  ex  did not correctly handle the inclusion of text input commands (that is,
       append, insert, and change)  in  executed  buffers.  POSIX.1‐2008  does  not  permit  this
       exclusion for consistency.

       Historically,  the  logical  contents  of  the buffer being executed did not change if the
       buffer itself were modified by the commands being executed; that is, buffer execution  did
       not support self-modifying code. POSIX.1‐2008 requires conformance to historical practice.

       Historically,  the @ command took a range of lines, and the @ buffer was executed once per
       line, with the current line ('.')  set  to  each  specified  line.  POSIX.1‐2008  requires
       conformance to historical practice.

       Some historical implementations did not notice if errors occurred during buffer execution.
       This, coupled with the ability to specify a range of lines for the ex @ command, makes  it
       trivial  to  cause  them  to  drop  core.  POSIX.1‐2008 requires that implementations stop
       buffer execution if any error occurs, if the specified  line  doesn't  exist,  or  if  the
       contents  of  the edit buffer itself are replaced (for example, the buffer executes the ex
       :edit command).

   Regular Expressions in ex
       Historical practice is that the characters in the replacement part of the last s  command—
       that  is,  those  matched  by  entering  a  '~' in the regular expression—were not further
       expanded by the regular expression engine. So, if  the  characters  contained  the  string
       "a.,"  they  would  match  'a'  followed  by  ".,"  and not 'a' followed by any character.
       POSIX.1‐2008 requires conformance to historical practice.

   Edit Options in ex
       The following paragraphs describe the historical behavior of some edit options  that  were
       not,  for  whatever  reason,  included  in  POSIX.1‐2008.   Implementations  are  strongly
       encouraged to only use these names if the functionality described here is fully supported.

       extended  The extended edit option has been used in some implementations of vi to  provide
                 extended  regular  expressions  instead of basic regular expressions This option
                 was omitted from POSIX.1‐2008 because it is not widespread historical practice.

       flash     The flash edit option historically caused the screen to flash instead of beeping
                 on  error.  This option was omitted from POSIX.1‐2008 because it is not found in
                 some historical implementations.

       hardtabs  The hardtabs edit option historically defined  the  number  of  columns  between
                 hardware  tab settings. This option was omitted from POSIX.1‐2008 because it was
                 believed to no longer be generally useful.

       modeline  The modeline (sometimes named modelines) edit option historically caused  ex  or
                 vi  to read the five first and last lines of the file for editor commands.  This
                 option is a security problem, and vendors are strongly encouraged to  delete  it
                 from historical implementations.

       open      The  open  edit  option historically disallowed the ex open and visual commands.
                 This  edit  option  was  omitted  because  these  commands   are   required   by
                 POSIX.1‐2008.

       optimize  The  optimize  edit option historically expedited text throughput by setting the
                 terminal to not do automatic <carriage-return>  characters  when  printing  more
                 than  one  logical  line  of  output.  This option was omitted from POSIX.1‐2008
                 because it was intended for terminals without  addressable  cursors,  which  are
                 rarely, if ever, still used.

       ruler     The  ruler  edit option has been used in some implementations of vi to present a
                 current row/column ruler for the user. This option was omitted from POSIX.1‐2008
                 because it is not widespread historical practice.

       sourceany The  sourceany edit option historically caused ex or vi to source start-up files
                 that were owned by users other than the user running the editor. This option  is
                 a  security problem, and vendors are strongly encouraged to remove it from their
                 implementations.

       timeout   The timeout edit option historically enabled the (now standard) feature of  only
                 waiting  for a short period before returning keys that could be part of a macro.
                 This feature was omitted from POSIX.1‐2008 because its behavior is now standard,
                 it is not widely useful, and it was rarely documented.

       verbose   The  verbose edit option has been used in some implementations of vi to cause vi
                 to output error messages for common errors; for example, attempting to move  the
                 cursor  past  the  beginning  or  end  of  the line instead of only alerting the
                 screen. (The historical vi only alerted the terminal and  presented  no  message
                 for  such  errors.  The  historical  editor  option terse did not select when to
                 present error messages, it only  made  existing  error  messages  more  or  less
                 verbose.) This option was omitted from POSIX.1‐2008 because it is not widespread
                 historical practice; however, implementors are encouraged to use it if they wish
                 to provide error messages for naive users.

       wraplen   The  wraplen  edit option has been used in some implementations of vi to specify
                 an automatic margin measured from the left margin  instead  of  from  the  right
                 margin.  This  is  useful  when  multiple  screen sizes are being used to edit a
                 single file. This option  was  omitted  from  POSIX.1‐2008  because  it  is  not
                 widespread  historical  practice; however, implementors are encouraged to use it
                 if they add this functionality.

   autoindent, ai
       Historically, the command 0a did not do any autoindentation,  regardless  of  the  current
       indentation  of  line  1.  POSIX.1‐2008 requires that any indentation present in line 1 be
       used.

   autoprint, ap
       Historically, the autoprint edit option was not completely consistent or based  solely  on
       modifications  to  the  edit buffer. Exceptions were the read command (when reading from a
       file, but not from a filter), the append, change, insert, global, and v commands,  all  of
       which  were  not  affected  by  autoprint,  and  the  tag  command,  which was affected by
       autoprint.  POSIX.1‐2008 requires conformance to historical practice.

       Historically, the autoprint option only applied to the last of multiple  commands  entered
       using <vertical-line> delimiters; for example, delete <newline> was affected by autoprint,
       but delete|version <newline> was not.  POSIX.1‐2008  requires  conformance  to  historical
       practice.

   autowrite, aw
       Appending the '!'  character to the ex next command to avoid performing an automatic write
       was not supported in historical implementations. POSIX.1‐2008 requires that  the  behavior
       match the other ex commands for consistency.

   ignorecase, ic
       Historical  implementations of case-insensitive matching (the ignorecase edit option) lead
       to counter-intuitive situations when uppercase characters were used in range  expressions.
       Historically, the process was as follows:

        1. Take a line of text from the edit buffer.

        2. Convert uppercase to lowercase in text line.

        3. Convert  uppercase  to  lowercase  in  regular  expressions, except in character class
           specifications.

        4. Match regular expressions against text.

       This would mean that, with ignorecase in effect, the text:

           The cat sat on the mat

       would be matched by

           /^the/

       but not by:

           /^[A-Z]he/

       For consistency with other commands implementing regular  expressions,  POSIX.1‐2008  does
       not permit this behavior.

   paragraphs, para
       The  ISO POSIX‐2:1993  standard  made  the  default  paragraphs  and sections edit options
       implementation-defined, arguing they were historically oriented to the UNIX  system  troff
       text  formatter,  and a ``portable user'' could use the {, }, [[, ]], (, and ) commands in
       open or visual mode and have the cursor stop in unexpected places. POSIX.1‐2008  specifies
       their values in the POSIX locale because the unusual grouping (they only work when grouped
       into two characters at a  time)  means  that  they  cannot  be  used  for  general-purpose
       movement, regardless.

   readonly
       Implementations  are encouraged to provide the best possible information to the user as to
       the read-only status of the file, with the exception that they  should  not  consider  the
       current  special  privileges of the process. This provides users with a safety net because
       they must force the overwrite of  read-only  files,  even  when  running  with  additional
       privileges.

       The  readonly  edit option specification largely conforms to historical practice. The only
       difference is that historical implementations did not notice that the  user  had  set  the
       readonly edit option in cases where the file was already marked read-only for some reason,
       and would therefore reinitialize the readonly edit option the next time  the  contents  of
       the edit buffer were replaced. This behavior is disallowed by POSIX.1‐2008.

   report
       The  requirement  that lines copied to a buffer interact differently than deleted lines is
       historical practice. For example, if the report edit option is set to 3, deleting 3  lines
       will cause a report to be written, but 4 lines must be copied before a report is written.

       The  requirement  that  the  ex global, v, open, undo, and visual commands present reports
       based on the total number of lines added or deleted during the command execution, and that
       commands  executed  by  the  global  and  v  commands  not  present reports, is historical
       practice. POSIX.1‐2008 extends historical practice by requiring that buffer  execution  be
       treated similarly. The reasons for this are two-fold. Historically, only the report by the
       last command executed from the buffer would be seen by the user, as each new report  would
       overwrite  the  last.  In addition, the standard developers believed that buffer execution
       had more in common with global and v commands than it did  with  other  ex  commands,  and
       should behave similarly, for consistency and simplicity of specification.

   showmatch, sm
       The  length of time the cursor spends on the matching character is unspecified because the
       timing capabilities of systems are often inexact and variable. The  time  should  be  long
       enough  for  the  user to notice, but not long enough for the user to become annoyed. Some
       implementations of vi have added a matchtime option that permits users to set  the  number
       of 0,1 second intervals the cursor pauses on the matching character.

   showmode
       The  showmode  option  has  been  used  in some historical implementations of ex and vi to
       display the current editing mode when in open or  visual  mode.  The  editing  modes  have
       generally   included  ``command''  and  ``input'',  and  sometimes  other  modes  such  as
       ``replace'' and ``change''. The string was usually displayed on the  bottom  line  of  the
       screen  at the far right-hand corner. In addition, a preceding '*' character often denoted
       whether the contents of the  edit  buffer  had  been  modified.  The  latter  display  has
       sometimes  been  part  of the showmode option, and sometimes based on another option. This
       option was not available in the 4 BSD historical implementation of vi, but was  viewed  as
       generally useful, particularly to novice users, and is required by POSIX.1‐2008.

       The   smd   shorthand   for  the  showmode  option  was  not  present  in  all  historical
       implementations of the editor.  POSIX.1‐2008 requires it, for consistency.

       Not all historical implementations of the editor displayed a mode string for command mode,
       differentiating  command  mode  from  text  input  mode  by  the absence of a mode string.
       POSIX.1‐2008  permits  this  behavior  for  consistency  with  historical  practice,   but
       implementations are encouraged to provide a display string for both modes.

   slowopen
       Historically, the slowopen option was automatically set if the terminal baud rate was less
       than 1200 baud, or if the baud rate was 1200 baud and the redraw option was not  set.  The
       slowopen option had two effects. First, when inserting characters in the middle of a line,
       characters after the cursor would not be pushed ahead, but would appear to be overwritten.
       Second,  when  creating  a  new  line  of  text, lines after the current line would not be
       scrolled down, but would appear to be overwritten. In both cases, ending text  input  mode
       would  cause  the  screen to be refreshed to match the actual contents of the edit buffer.
       Finally, terminals that were sufficiently intelligent caused  the  editor  to  ignore  the
       slowopen  option.  POSIX.1‐2008  permits  most  historical  behavior, extending historical
       practice to require slowopen behaviors if the edit option is set by the user.

   tags
       The default path for tags files is left unspecified as implementations may have their  own
       tags  implementations  that  do  not  correspond  to the historical ones. The default tags
       option value should probably at least include the file ./tags.

   term
       Historical implementations of ex and vi ignored changes to the term edit option after  the
       initial  terminal  information  was  loaded.  This  is permitted by POSIX.1‐2008; however,
       implementations are encouraged to permit the user to modify their  terminal  type  at  any
       time.

   terse
       Historically,  the terse edit option optionally provided a shorter, less descriptive error
       message, for some error messages. This is permitted, but not  required,  by  POSIX.1‐2008.
       Historically,  most common visual mode errors (for example, trying to move the cursor past
       the end of a line) did not result in an error message, but simply  alerted  the  terminal.
       Implementations  wishing  to provide messages for novice users are urged to do so based on
       the edit option verbose, and not terse.

   window
       In historical implementations, the default for the window edit option  was  based  on  the
       baud rate as follows:

        1. If  the  baud  rate was less than 1200, the edit option w300 set the window value; for
           example, the line:

               set w300=12

           would set the window option to 12 if the baud rate was less than 1200.

        2. If the baud rate was equal to 1200, the edit option w1200 set the window value.

        3. If the baud rate was greater than 1200, the edit option w9600 set the window value.

       The w300, w1200, and w9600  options  do  not  appear  in  POSIX.1‐2008  because  of  their
       dependence on specific baud rates.

       In  historical  implementations,  the size of the window displayed by various commands was
       related to, but not necessarily the same as, the window edit option. For example, the size
       of  the window was set by the ex command visual 10, but it did not change the value of the
       window edit option. However, changing the value of the window edit option did  change  the
       number  of  lines that were displayed when the screen was repainted. POSIX.1‐2008 does not
       permit this behavior in the interests of consistency and simplicity of specification,  and
       requires  that  all  commands  that change the number of lines that are displayed do it by
       setting the value of the window edit option.

   wrapmargin, wm
       Historically, the wrapmargin option did not affect maps inserting characters that also had
       associated  counts;  for  example  :map K 5aABC DEF.  Unfortunately, there are widely used
       maps that depend on this behavior.   For  consistency  and  simplicity  of  specification,
       POSIX.1‐2008 does not permit this behavior.

       Historically,  wrapmargin  was calculated using the column display width of all characters
       on the screen. For example, an implementation using "^I"  to  represent  <tab>  characters
       when  the  list edit option was set, where '^' and 'I' each took up a single column on the
       screen, would calculate the wrapmargin based on a value of 2 for each <tab>.   The  number
       edit  option  similarly  changed  the  effective length of the line as well.  POSIX.1‐2008
       requires conformance to historical practice.

       Earlier versions of this standard allowed for implementations with bytes other than  eight
       bits, but this has been modified in this version.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Section 2.9.1.1, Command Search and Execution, ctags, ed, sed, sh, stty, vi

       The  Base  Definitions  volume of POSIX.1‐2017, Table 5-1, Escape Sequences and Associated
       Actions, Chapter 8, Environment Variables, Section 9.3, Basic Regular Expressions, Section
       12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1‐2017, access()

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1-2017, Standard for Information Technology -- Portable  Operating  System  Interface
       (POSIX),  The  Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by
       the Institute of Electrical and Electronics Engineers, Inc and The  Open  Group.   In  the
       event  of  any  discrepancy  between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or  formatting errors that appear in this page are most likely to have
       been introduced during the conversion of the source files to man page  format.  To  report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .