Provided by: ksh93u+m_1.0.0~beta.2-1_amd64 bug

NAME

       ksh, rksh - KornShell, a standard/restricted command and programming language

SYNOPSIS

       ksh [ ±abcefhiklmnprstuvxBCDEGH ] [ ±o option ] ... [ - ] [ arg ... ]
       rksh [ ±abcefhiklmnpstuvxBCDEGH ] [ ±o option ] ... [ - ] [ arg ... ]

DESCRIPTION

       Ksh is a command and programming language that executes commands read from a terminal or a file.  Rksh is
       a restricted version of the command interpreter ksh; it is used to  set  up  login  names  and  execution
       environments  whose  capabilities  are  more controlled than those of the standard shell.  See Invocation
       below for the meaning of arguments to the shell.

   Definitions.
       A metacharacter is one of the following characters:

              ;   &   (   )   |   <   >   new-line   space   tab

       A blank is a tab or a space.  An identifier is a sequence of letters,  digits,  or  underscores  starting
       with  a  letter  or  underscore.   Identifiers  are  used  as components of variable names.  A vname is a
       sequence of one or more identifiers separated by a . and optionally preceded by a ..  Vnames are used  as
       function  and  variable  names.  A word is a sequence of characters from the character set defined by the
       current locale, excluding non-quoted metacharacters.

       A command is a sequence of characters in the syntax of the shell language.  The shell reads each  command
       and carries out the desired action either directly or by invoking separate utilities.  A built-in command
       is a command that is carried out by the shell itself without creating a separate process.  Some  commands
       are  built-in  purely  for convenience and are not documented here.  Built-ins that cause side effects in
       the shell environment and built-ins that are found before performing a path search (see Execution  below)
       are  documented  here.   For  historical  reasons,  some of these built-ins behave differently than other
       built-ins and are called special built-ins.

   Commands.
       A simple-command is a list of variable assignments (see Variable Assignments  below)  or  a  sequence  of
       blank  separated  words  which may be preceded by a list of variable assignments (see Environment below).
       The first word specifies the name of the  command  to  be  executed.   Except  as  specified  below,  the
       remaining words are passed as arguments to the invoked command.  The command name is passed as argument 0
       (see exec(2)).  The value of a simple-command is its  exit  status;  0-255  if  it  terminates  normally;
       256+signum  if  it  terminates abnormally (the name of the signal corresponding to the exit status can be
       obtained via the -l option of the kill built-in utility).

       A pipeline is a sequence of one or more commands separated by |.  The standard output of each command but
       the  last  is  connected  by  a  pipe(2) to the standard input of the next command.  Each command, except
       possibly the last, is run as a separate process; the shell waits for the last command to terminate.   The
       exit  status  of a pipeline is the exit status of the last command unless the pipefail option is enabled.
       Each pipeline can be preceded by the reserved word !  which causes the exit status  of  the  pipeline  to
       become 0 if the exit status of the last command is non-zero, and 1 if the exit status of the last command
       is 0.

       A list is a sequence of one or more pipelines separated by ;, &, |&, &&, or ||, and optionally terminated
       by  ;,  &, or |&.  Of these five symbols, ;, &, and |& have equal precedence, which is lower than that of
       && and ||.  The symbols && and ||  also  have  equal  precedence.   A  semicolon  (;)  causes  sequential
       execution  of  the  preceding  pipeline;  an ampersand (&) causes asynchronous execution of the preceding
       pipeline (i.e., the shell does not wait for that pipeline to finish).  The symbol |& causes  asynchronous
       execution  of  the  preceding  pipeline with a two-way pipe established to the parent shell; the standard
       input and output of the spawned pipeline can be written to and read from by the parent shell by  applying
       the  redirection  operators  <&  and  >&  with  arg  p to commands and by using -p option of the built-in
       commands read and print described later.  The symbol && (||) causes the list following it to be  executed
       only  if  the  preceding pipeline returns a zero (non-zero) value.  One or more new-lines may appear in a
       list instead of a semicolon, to delimit a command.  The first item  of the first pipeline of a list  that
       is  a  simple  command  not  beginning with a redirection, and not occurring within a while, until, or if
       list, can be preceded by a semicolon.  This semicolon is ignored unless the showme option is  enabled  as
       described with the set built-in below.

       A  command  is  either  a  simple-command  or  one  of the following.  Unless otherwise stated, the value
       returned by a command is that of the last simple-command executed in the command.

       for vname [ in word ... ] ;do list ;done
              Each time a for command is executed, vname is set to the next word taken from the  in  word  list.
              If  in  word  ...   is omitted, then the for command executes the do list once for each positional
              parameter that is set starting from 1 (see Parameter Expansion below).  Execution ends when  there
              are no more words in the list.

       for (( [expr1] ; [expr2] ; [expr3] )) ;do list ;done
              The  arithmetic  expression  expr1  is  evaluated  first  (see  Arithmetic Evaluation below).  The
              arithmetic expression expr2 is repeatedly evaluated until it evaluates to zero and when  non-zero,
              list  is  executed  and  the arithmetic expression expr3 evaluated.  If any expression is omitted,
              then it behaves as if it evaluated to 1.

       select vname [ in word ... ] ;do list ;done
              A select command prints on standard error (file descriptor 2) the set of words, each preceded by a
              number.   If  in  word  ...   is  omitted, then the positional parameters starting from 1 are used
              instead (see Parameter Expansion below).  The PS3 prompt is printed and a line is  read  from  the
              standard input.  If this line consists of the number of one of the listed words, then the value of
              the variable vname is set to the word corresponding to this number.  If this line  is  empty,  the
              selection  list  is printed again.  Otherwise the value of the variable vname is set to null.  The
              contents of the line read from standard input is  saved  in  the  variable  REPLY.   The  list  is
              executed for each selection until a break or end-of-file is encountered.  If the REPLY variable is
              set to null by the execution of list, then the selection list is printed before displaying the PS3
              prompt for the next selection.

       case word in [ [(]pattern [ | pattern ] ... ) list ;; ] ... esac
              A case command executes the list associated with the first pattern that matches word.  The form of
              the patterns is the same as that used for pathname expansion (see Pathname Expansion below).   The
              ;;  operator  causes  execution  of  case  to  terminate.   If  ;& is used in place of ;; the next
              subsequent list, if any,  is executed.

       if list ;then list [ ;elif list ;then list ] ... [ ;else list ] ;fi
              The list following if is executed and, if it returns a zero exit status, the  list  following  the
              first then is executed.  Otherwise, the list following elif is executed and, if its value is zero,
              the list following the next then is executed.  Failing each successive elif list, the else list is
              executed.   If the if list has non-zero exit status and there is no else list, then the if command
              returns a zero exit status.

       while list ;do list ;done
       until list ;do list ;done
              A while command repeatedly executes the while list and, if the exit status of the last command  in
              the  list  is zero, executes the do list; otherwise the loop terminates.  If no commands in the do
              list are executed, then the while command returns a zero exit status; until may be used  in  place
              of while to negate the loop termination test.

       ((expression))
              The  expression  is  evaluated  using the rules for arithmetic evaluation described below.  If the
              value of the arithmetic expression is non-zero, the exit status is 0, otherwise the exit status is
              1.

       (list)
              Execute  list  in  a separate environment.  Note, that if two adjacent open parentheses are needed
              for nesting, a space must be inserted to avoid evaluation as an arithmetic  command  as  described
              above.

       { list;}
              list  is simply executed.  Note that unlike the metacharacters ( and ), { and } are reserved words
              and must occur at the beginning of a line or after a ; in order to be recognized.

       [[ expression ]]
              Evaluates expression and returns a zero exit status when  expression  is  true.   See  Conditional
              Expressions below, for a description of expression.

       function varname { list ;}
       varname () { list ;}
              Define  a  function  which  is  referenced  by varname.  A function whose varname contains a .  is
              called a discipline function and the portion of the varname preceding the last .  must refer to an
              existing  variable.  The body of the function is the list of commands between { and }.  A function
              defined with the function varname syntax can also be used as an argument to the .  special  built-
              in command to get the equivalent behavior as if the varname() syntax were used to define it.  (See
              Functions below.)

       namespace identifier { list ;}
              Defines or uses the name space identifier and runs the commands in list in this name space.   (See
              Name Spaces below.)

       & [ name [ arg... ]  ]
              Causes  subsequent list commands terminated by & to be placed in the background job pool name.  If
              name is omitted a default unnamed pool is used.  Commands  in  a  named  background  pool  may  be
              executed remotely.

       time [ pipeline ]
              If  pipeline  is  omitted  the  user  and  system  time  for the current shell and completed child
              processes is printed on standard error.  Otherwise, pipeline is executed and the elapsed  time  as
              well  as  the  user and system time are printed on standard error.  The TIMEFORMAT variable may be
              set to a format string that specifies how the timing information should be displayed.   See  Shell
              Variables below for a description of the TIMEFORMAT variable.

       The  following  reserved  words are recognized as reserved only when they are the first word of a command
       and are not quoted:

       if then else elif fi case esac for while until do done { } function select time [[ ]] !

   Variable Assignments.
       One or more variable assignments can start a simple command or can be arguments  to  the  typeset,  enum,
       export,  or readonly special built-in commands as well as to other declaration commands created as types.
       The syntax for an assignment is of the form:

       varname=word
       varname[word]=word
              No space is permitted between varname and the = or between = and word.

       varname=(assign_list)
              No space is permitted between varname and the  =.   The  variable  varname  is  unset  before  the
              assignment.  An assign_list can be one of the following:
                      word ...
                             Indexed array assignment.
                      [word]=word ...
                             Associative  array  assignment.   If  preceded  by  typeset  -a this will create an
                             indexed array instead.
                      assignment ...
                             Compound variable assignment.   This  creates  a  compound  variable  varname  with
                             subvariables  of  the  form  varname.name,  where  name  is  the  name  portion  of
                             assignment.  The value  of  varname  will  contain  all  the  assignment  elements.
                             Additional  assignments  made  to subvariables of varname will also be displayed as
                             part of the value of varname.  If no assignments are specified, varname will  be  a
                             compound variable allowing subsequence child elements to be defined.
                      typeset [options] assignment ...
                             Nested  variable  assignment.   Multiple assignments can be specified by separating
                             each of them with a ;.  The previous value is unset before the  assignment.   Other
                             declaration  commands such as readonly, enum, and other declaration commands can be
                             used in place of typeset.
                      . filename
                             Include the assignment commands contained in filename.

       In addition, a += can be used in place of the = to signify adding to or appending to the previous  value.
       When  += is applied to an arithmetic type, word is evaluated as an arithmetic expression and added to the
       current value.  When applied to a string variable, the value defined by word is appended  to  the  value.
       For  compound assignments, the previous value is not unset and the new values are appended to the current
       ones provided that the types are compatible.

       The right hand side of a variable assignment  undergoes  all  the  expansion  listed  below  except  word
       splitting,  brace  expansion,  and  pathname  expansion.   When  the left hand side is an assignment is a
       compound variable and the right hand is the name of a compound variable, the  compound  variable  on  the
       right will be copied or appended to the compound variable on the left.

   Comments.
       A word beginning with # causes that word and all the following characters up to a new-line to be ignored.

   Aliasing.
       The  first  word  of  each command is replaced by the text of an alias if an alias for this word has been
       defined.  An  alias  name  consists  of  any  number  of  characters  excluding  metacharacters,  quoting
       characters,  file  expansion  characters,  parameter  expansion  and command substitution characters, the
       characters /  and  =.   The  replacement  string  can  contain  any  valid  shell  script  including  the
       metacharacters  listed  above.   The first word of each command in the replaced text, other than any that
       are in the process of being replaced, will be tested for aliases.  If the last  character  of  the  alias
       value  is a blank then the word following the alias will also be checked for alias substitution.  Aliases
       can be used to redefine built-in commands but cannot be used to redefine the reserved words listed above.
       Aliases can be created and listed with the alias command and can be removed with the unalias command.

       Aliasing  is  performed  when  scripts are read, not while they are executed.  Therefore, for an alias to
       take effect, the alias definition command has to be executed before  the  command  which  references  the
       alias is read.

       The  following aliases are automatically preset when the shell is invoked as an interactive shell, unless
       invoked in POSIX compliance mode (see Invocation below).  Preset aliases can be unset or redefined.
                           history=′hist -l′
                           r=′hist -s′

   Tilde Expansion.
       After alias substitution is performed, each word is checked to see if it begins with an unquoted .   For
       tilde  expansion,  word  also  refers to the word portion of parameter expansion (see Parameter Expansion
       below).  If a word is preceded by a tilde, then it is checked up to a / to see if it matches a user  name
       in  the  password database (see getpwname(3)).  If a match is found, the  and the matched login name are
       replaced by the login directory of the matched user.  If no match is found, the  original  text  is  left
       unchanged.   A   by itself, or in front of a /, is replaced by $HOME, unless the HOME variable is unset,
       in which case the current user's home directory as configured in the  operating  system  is  used.   A  
       followed by a + or - is replaced by $PWD or $OLDPWD respectively.

       In  addition,  when  expanding a variable assignment (see Variable Assignments above), tilde expansion is
       attempted when the value of the assignment begins with a , and when a  appears after a  :.   A  :  also
       terminates a user name following a .

       The  tilde  expansion  mechanism  may be extended or modified by defining one of the discipline functions
       .sh.tilde.set or .sh.tilde.get (see Functions and Discipline Functions below).  If  either  exists,  then
       upon  encountering a tilde word to expand, that function is called with the tilde word assigned to either
       .sh.value (for the .sh.tilde.set function) or .sh.tilde (for  the  .sh.tilde.get  function).   Performing
       tilde  expansion  within a discipline function will not recursively call that function, but default tilde
       expansion remains active, so literal tildes should still be quoted where required.  Either  function  may
       assign  a  replacement  string  to .sh.value.  If this value is non-empty and does not start with a , it
       replaces the default tilde expansion when the function terminates.  Otherwise,  the  tilde  expansion  is
       left unchanged.

   Command Substitution.
       The standard output from a command list enclosed in parentheses preceded by a dollar sign ( $(list) ), or
       in a brace group preceded by a dollar sign ( ${ list;} ), or in a pair of grave accents (``) may be  used
       as part or all of a word; trailing new-lines are removed.  In the second case, the { and } are treated as
       a reserved words so that { must be followed by a blank and } must appear at the beginning of the line  or
       follow a ;.  In the third (obsolete) form, the string between the quotes is processed for special quoting
       characters before the command is executed (see Quoting below).  The command substitution $(cat file)  can
       be  replaced  by  the equivalent but faster $(<file).  The command substitution $(n<#) will expand to the
       current byte offset for file descriptor n.  Except for the second form, the command  list  is  run  in  a
       subshell  so that no side effects are possible.  For the second form, the final } will be recognized as a
       reserved word after any token.

   Arithmetic Expansion.
       An arithmetic expression enclosed in double parentheses preceded by a dollar sign ( $(()) )  is  replaced
       by the value of the arithmetic expression within the double parentheses.

   Process Substitution.
       Each  command  argument  of the form <(list) or >(list) will run process list asynchronously connected to
       some file in /dev/fd if this directory exists, or else a fifo a temporary directory.  The  name  of  this
       file  will  become the argument to the command.  If the form with > is selected then writing on this file
       will provide input for list.  If < is used, then the file passed as an argument will contain  the  output
       of the list process.  For example,

              paste <(cut -f1 file1) <(cut -f3 file2) | tee >(process1) >(process2)

       cuts  fields  1 and 3 from the files file1 and file2 respectively, pastes the results together, and sends
       it to the processes process1 and process2, as well as putting it onto the standard output.  Note that the
       file,  which  is  passed  as  an  argument  to  the command, is a UNIX pipe(2) so programs that expect to
       lseek(2) on the file will not work.

       Process substitution of the form <(list) can also be used with the < redirection  operator  which  causes
       the output of list to be standard input or the input for whatever file descriptor is specified.

   Parameter Expansion.
       A  parameter  is  a  variable,  one  or more digits, or any of the characters *, @, #, ?, -, $, and !.  A
       variable is denoted by a vname.  To create a variable whose vname contains a ., a  variable  whose  vname
       consists  of  everything  before  the last . must already exist.  A variable has a value and zero or more
       attributes.  Variables can be assigned values and  attributes  by  using  the  typeset  special  built-in
       command.   The  attributes  supported  by the shell are described later with the typeset special built-in
       command.  Exported variables pass their attributes to the environment so that a newly invoked ksh that is
       a  child  or  exec'd  process of the current shell will automatically import them, unless the posix shell
       option is on.

       The shell supports both indexed and associative arrays.  An element of an array variable is referenced by
       a  subscript.   A  subscript  for an indexed array is denoted by an arithmetic expression (see Arithmetic
       Evaluation below) between a [ and a ].  To assign values to an indexed array, use  vname=(value  ...)  or
       set  -A  vname   value  ... .  The value of all non-negative subscripts must be in the range of 0 through
       4,194,303.  A negative subscript is treated as an offset from the maximum current index  +1  so  that  -1
       refers  to  the  last  element.   Indexed  arrays can be declared with the -a option to typeset.  Indexed
       arrays need not be declared.  Any reference to a variable with a valid subscript is legal  and  an  array
       will be created if necessary.

       An  associative  array is created with the -A option to typeset.  A subscript for an associative array is
       denoted by a string enclosed between [ and ].

       Referencing any array without a subscript is equivalent to referencing the array with subscript 0.

       The value of a variable may be assigned by writing:

              vname=value [ vname=value ] ...

       or
              vname[subscript]=value [ vname[subscript]=value ] ...
       Note that no space is allowed before or after the =.
       Attributes assigned by the typeset special built-in command apply to all elements of the array.  An array
       element  can  be  a  simple variable, a compound variable or an array variable.  An element of an indexed
       array can be either an indexed array or an associative array.  An element of  an  associative  array  can
       also be either.  To refer to an array element that is part of an array element, concatenate the subscript
       in brackets.  For example, to refer to the foobar element of an associative array that is defined as  the
       third element of the indexed array, use ${vname[3][foobar]}
       A  nameref  is  a  variable  that  is  a reference to another variable.  A nameref is created with the -n
       attribute of typeset.  The value of the variable at the time of the typeset command becomes the  variable
       that will be referenced whenever the nameref variable is used.  The name of a nameref cannot contain a ..
       When a variable or function name contains a ., and the portion of the name up to the first . matches  the
       name of a nameref, the variable referred to is obtained by replacing the nameref portion with the name of
       the variable referenced by the nameref.  If a nameref is used  as  the  index  of  a  for  loop,  a  name
       reference  is established for each item in the list.  A nameref provides a convenient way to refer to the
       variable inside a function whose name is passed as an argument to a function.  For example, if  the  name
       of a variable is passed as the first argument to a function, the command
              typeset -n var=$1
       inside  the  function  causes  references  and assignments to var to be references and assignments to the
       variable whose name has been passed to the function.
       If any of the floating point attributes, -E, -F, or -X, or the integer attribute, -i, is set  for  vname,
       then the value is subject to arithmetic evaluation as described below.
       Positional parameters, parameters denoted by a number, may be assigned values with the set special built-
       in command.  Parameter $0 is set from argument zero when the shell is invoked.
       The character $ is used to introduce substitutable parameters.
       ${parameter}
              The shell reads all the characters from ${ to the matching } as part of the same word even  if  it
              contains  braces  or  metacharacters.   The  value,  if any, of the parameter is substituted.  The
              braces are required when parameter is followed by a letter, digit, or underscore that is not to be
              interpreted  as  part  of  its  name,  when  the  variable name contains a ..  The braces are also
              required when a variable is subscripted unless it  is  part  of  an  Arithmetic  Expression  or  a
              Conditional  Expression.  If parameter is one or more digits then it is a positional parameter.  A
              positional parameter of more than one digit must be enclosed in braces.  If parameter is *  or  @,
              then  all  the  positional  parameters,  starting  with  $1, are substituted (separated by a field
              separator character).  If an array vname with last subscript * @, or for  indexed  arrays  of  the
              form  sub1  ..   sub2.   is  used,  then  the value for each of the elements between sub1 and sub2
              inclusive (or all elements for * and @) is substituted, separated by the first  character  of  the
              value of IFS.
       ${#parameter}
              If parameter is * or @, the number of positional parameters is substituted.  Otherwise, the length
              of the value of the parameter is substituted.
       ${#vname[*]}
       ${#vname[@]}
              The number of elements in the array vname is substituted.

       ${@vname}
              Expands to the type name (See Type Variables  below) or attributes of the variable referred to  by
              vname.
       ${!vname}
              Expands to the name of the variable referred to by vname.  This will be vname except when vname is
              a name reference.
       ${!vname[subscript]}
              Expands to name of the subscript unless subscript is *, @.  or of the form sub1  ..   sub2.   When
              subscript  is  *, the list of array subscripts for vname is generated.  For a variable that is not
              an array, the value is 0 if the variable is set.  Otherwise it is null.  When subscript is @, same
              as above, except that when used in double quotes, each array subscript yields a separate argument.
              When subscript is of the form sub1 ..  sub2 it expands to the list of subscripts between sub1  and
              sub2 inclusive using the same quoting rules as @.
       ${!prefix@}
       ${!prefix*}
              These  both  expand  to  the names of the variables whose names begin with prefix.  The expansions
              otherwise work like $@ and $*, respectively (see under Quoting below).
       ${parameter:-word}
              If parameter is set and is non-null then substitute its value; otherwise substitute word.
       ${parameter:=word}
              If parameter is not set or is null then set it to  word;  the  value  of  the  parameter  is  then
              substituted.  Positional parameters may not be assigned to in this way.
       ${parameter:?word}
              If parameter is set and is non-null then substitute its value; otherwise, print word and exit from
              the shell (if not interactive).  If word is omitted then a standard message is printed.
       ${parameter:+word}
              If parameter is set and is non-null then substitute word; otherwise substitute nothing.
       In the above, word is not evaluated unless it is to be used as the substituted string, so  that,  in  the
       following example, pwd is executed only if d is not set or is null:
              print ${d:-$(pwd)}
       If the colon ( : ) is omitted from the above expressions, then the shell only checks whether parameter is
       set or not.
       ${parameter:offset:length}
       ${parameter:offset}
              Expands to the portion of the value of parameter starting  at  the  character  (counting  from  0)
              determined  by  expanding  offset  as  an  arithmetic  expression  and consisting of the number of
              characters determined by the arithmetic expression defined by length.  In  the  second  form,  the
              remainder  of the value is used.  If A negative offset counts backwards from the end of parameter.
              Note that one or more blanks is required in front of a  minus  sign  to  prevent  the  shell  from
              interpreting  the  operator as :-.  If parameter is * or @, or is an array name indexed by * or @,
              then offset and length refer to the array index and number of elements respectively.   A  negative
              offset  is taken relative to one greater than the highest subscript for indexed arrays.  The order
              for associative arrays is unspecified.
       ${parameter#pattern}
       ${parameter##pattern}
              If the shell pattern matches the beginning of the value of  parameter,  then  the  value  of  this
              expansion  is  the value of the parameter with the matched portion deleted; otherwise the value of
              this parameter is substituted.  In the first form the smallest matching pattern is deleted and  in
              the  second  form  the  largest  matching pattern is deleted.  When parameter is @, *, or an array
              variable with subscript @ or *, the substring operation is applied to each element in turn.

       ${parameter%pattern}
       ${parameter%%pattern}
              If the shell pattern matches the end of the value of parameter, then the value of  this  expansion
              is  the  value  of  the parameter with the matched part deleted; otherwise substitute the value of
              parameter.  In the first form the smallest matching pattern is deleted and in the second form  the
              largest  matching pattern is deleted.  When parameter is @, *, or an array variable with subscript
              @ or *, the substring operation is applied to each element in turn.

       ${parameter/pattern/string}
       ${parameter//pattern/string}
       ${parameter/#pattern/string}
       ${parameter/%pattern/string}
              Expands parameter and replaces  the  longest  match  of  pattern  with  the  given  string.   Each
              occurrence  of  \n  in  string  is  replaced  by  the  portion  of parameter that matches the n-th
              subpattern.  In the first form, only the first occurrence of pattern is replaced.  In  the  second
              form,  each  match  for  pattern  is  replaced  by the given string.  The third form restricts the
              pattern match to the beginning of the string while the fourth form restricts the pattern match  to
              the  end  of  the  string.  When string is null, the pattern will be deleted and the / in front of
              string may be omitted.  When parameter is @, *, or an array variable with subscript @  or  *,  the
              substitution  operation  is  applied to each element in turn.  In this case, the string portion of
              word will be re-evaluated for each element.

   Shell Variables.
       The following parameters are automatically set by the shell:
              #      The number of positional parameters in decimal.
              -      Options supplied to the shell on invocation or by the set command.
              ?      The exit status returned by the last executed command. Its meaning depends on  the  command
                     or function that defines it, but there are conventions that other commands often depend on:
                     zero typically means 'success' or 'true', one typically means 'non-success' or 'false', and
                     a  value  greater  than  one  typically  indicates  some  kind  of  error. Only the 8 least
                     significant bits of $? (values 0 to 255) are preserved when the exit status is passed on to
                     a  parent process, but within the same (sub)shell environment, it is a signed integer value
                     with a range of possible values as shown  by  the  commands  getconf  INT_MIN  and  getconf
                     INT_MAX.  Shell  functions  that run in the current environment may return status values in
                     this range.
              $      The process ID of the main shell process. Note  that  this  value  will  not  change  in  a
                     subshell, even if the subshell runs in a different process.  See also .sh.pid.
              _      Initially,  the value of _ is an absolute pathname of the shell or script being executed as
                     passed in the environment.  Subsequently it is assigned the last argument of  the  previous
                     command.  This parameter is not set for commands which are asynchronous.  This parameter is
                     also used to hold the name of the  matching  MAIL  file  when  checking  for  mail.   While
                     defining  a  compound  variable  or a type, _ is initialized as a reference to the compound
                     variable or type.  When a discipline function is invoked, _ is initialized as  a  reference
                     to  the  variable associated with the call to this function.  Finally when _ is used as the
                     name of the first variable of a type definition, the new type is derived from the  type  of
                     the first variable. (See Type Variables  below.)
              !      The  process  id  or the pool name and job number of the last background command invoked or
                     the most recent job put in the background with the bg built-in  command.   Background  jobs
                     started  in  a  named  pool will be in the form pool.number where pool is the pool name and
                     number is the job number within that pool.
              .sh.command
                     When processing a DEBUG trap, this variable contains the current command line that is about
                     to  run.   The  value  is  in  the same format as the output generated by the xtrace option
                     (minus the preceding PS4 prompt).
              .sh.edchar
                     This variable contains the value of the keyboard character (or sequence  of  characters  if
                     the  first  character  is  an ESC, ASCII 033) that has been entered when processing a KEYBD
                     trap (see Key Bindings below).  If the value is changed as part of the  trap  action,  then
                     the new value replaces the key (or key sequence) that caused the trap.
              .sh.edcol
                     The character position of the cursor at the time of the most recent KEYBD trap.
              .sh.edmode
                     The  value  is  set  to  ESC when processing a KEYBD trap while in vi insert mode.  (See Vi
                     Editing Mode  below.)  Otherwise, .sh.edmode is null when processing a KEYBD trap.
              .sh.edtext
                     The characters in the input buffer at the time of the most recent KEYBD trap.  The value is
                     null when not processing a KEYBD trap.
              .sh.file
                     The pathname of the file that contains the current command.
              .sh.fun
                     The name of the current function that is being executed.
              .sh.level
                     Set  to  the  current function depth.  This can be changed inside a DEBUG trap and will set
                     the context to the specified level.
              .sh.lineno
                     Set during a DEBUG trap to the line number for the caller of each function.
              .sh.match
                     An indexed  array  which  stores  the  most  recent  match  and  subpattern  matches  after
                     conditional  pattern  matches that match and after variables expansions using the operators
                     #, %, or /.  The 0-th element stores the complete match and the i-th.  element  stores  the
                     i-th submatch.  The .sh.match variable becomes unset when the variable that has expanded is
                     assigned a new value.
              .sh.math
                     Used for defining arithmetic functions (see Arithmetic Evaluation  below)  and  stores  the
                     list of user defined arithmetic functions.
              .sh.name
                     Set to the name of the variable at the time that a discipline function is invoked.
              .sh.subscript
                     Set  to  the  name  subscript  of  the  variable  at the time that a discipline function is
                     invoked.
              .sh.subshell
                     The current depth for subshells and command substitution.
              .sh.pid
                     Set to the process ID of the current  shell.   This  is  distinct  from  $$  as  in  forked
                     subshells  this  is  set  to  the  process ID of the subshell instead of the parent shell's
                     process ID.  In virtual subshells .sh.pid retains its previous value.
              .sh.value
                     Set to the value of the variable at the time that the set or append discipline function  is
                     invoked.   When  a  user  defined arithmetic function is invoked, the value of .sh.value is
                     saved and .sh.value is set to long double precision floating point.  .sh.value is  restored
                     when the function returns.
              .sh.version
                     Set to a value that identifies the version of this shell.
              KSH_VERSION
                     A name reference to .sh.version.
              LINENO The current line number within the script or function being executed.
              OLDPWD The previous working directory set by the cd command.
              OPTARG The value of the last option argument processed by the getopts built-in command.
              OPTIND The index of the last option argument processed by the getopts built-in command.
              PPID   The process id of the parent of the shell.
              PWD    The present working directory set by the cd command.
              RANDOM Each  time  this  variable is referenced, a random integer, uniformly distributed between 0
                     and 32767, is generated.  The sequence of random numbers can be initialized by assigning  a
                     numeric value to RANDOM.
              REPLY  This  variable  is  set  by  the  select statement and by the read built-in command when no
                     arguments are supplied.
              SECONDS
                     Each time this variable is referenced, the number of  seconds  since  shell  invocation  is
                     returned.   If  this  variable  is assigned a value, then the value returned upon reference
                     will be the value that was assigned plus the number of seconds since the assignment.
              SHLVL  An integer variable that is incremented and exported each time the shell  is  invoked.   If
                     SHLVL is not in the environment when the shell is invoked, it is set to 1.

       The following variables are used by the shell:
              CDPATH The search path for the cd command.
              COLUMNS
                     If  this  variable is set, the value is used to define the width of the edit window for the
                     shell edit modes and for printing select lists.
              EDITOR If the VISUAL variable is not set, the value of this  variable  will  be  checked  for  the
                     patterns  as  described with VISUAL below and the corresponding editing option (see Special
                     Command set below) will be turned on.
              ENV    If this variable is set, then parameter expansion,  command  substitution,  and  arithmetic
                     expansion  are  performed  on the value to generate the pathname of the script that will be
                     executed when the shell is invoked interactively (see  Invocation  below).   This  file  is
                     typically  used for alias and function definitions.  The default value is $HOME/.kshrc.  On
                     systems that support a system wide  /etc/ksh.kshrc initialization  file,  if  the  filename
                     generated  by  the  expansion of ENV begins with /./ or ././ the system wide initialization
                     file will not be executed.
              FCEDIT Obsolete name for the default editor name for the hist command.  FCEDIT is  not  used  when
                     HISTEDIT is set.
              FIGNORE
                     A  pattern  that defines the set of filenames that will be ignored when performing filename
                     matching.
              FPATH  The search path for function definitions.  The directories in this path are searched for  a
                     file with the same name as the function or command when a function with the -u attribute is
                     referenced and when a command is not found.  If an executable file with the  name  of  that
                     command  is  found,  then it is read and executed in the current environment.  Unlike PATH,
                     the current directory must be represented explicitly  by  .   rather  than  by  adjacent  :
                     characters or a beginning or ending :.
              HISTCMD
                     Number of the current command in the history file.
              HISTEDIT
                     Name for the default editor name for the hist command.
              HISTFILE
                     If  this  variable  is set when the shell is invoked, then the value is the pathname of the
                     file that will be used to store the command history (see Command Re-entry below).
              HISTSIZE
                     If this variable is set when the shell is invoked, then the number  of  previously  entered
                     commands  that  are  accessible by this shell will be greater than or equal to this number.
                     The default is 512.
              HOME   The default argument (home directory) for the cd command.
              IFS    Internal field separators, normally space, tab, and new-line that are used to separate  the
                     results  of  command  substitution  or  parameter expansion and to separate fields with the
                     built-in command read.  The first character  of  the  IFS  variable  is  used  to  separate
                     arguments  for  the  "$*"  expansion (see Quoting below).  Each single occurrence of an IFS
                     character in the string to be split, that is not in the isspace character  class,  and  any
                     adjacent  characters  in IFS that are in the isspace character class, delimit a field.  One
                     or more characters in IFS that belong to the isspace character class, delimit a field.   In
                     addition, if the same isspace character appears consecutively inside IFS, this character is
                     treated as if it were not in the isspace  class,  so  that  if  IFS  consists  of  two  tab
                     characters, then two adjacent tab characters delimit a null field.
              JOBMAX This  variable  defines  the maximum number running background jobs that can run at a time.
                     When this limit is reached, the shell will wait for a job to complete before starting a new
                     job.
              LANG   This  variable  determines  the  locale category for any category not specifically selected
                     with a variable starting with LC_ or LANG.
              LC_ALL This variable overrides the value of the LANG variable and any other LC_ variable.
              LC_COLLATE
                     This variable determines the locale category for character collation information.
              LC_CTYPE
                     This variable  determines  the  locale  category  for  character  handling  functions.   It
                     determines the character classes for pattern matching (see Pathname Expansion below).
              LC_NUMERIC
                     This variable determines the locale category for the decimal point character.
              LINES  If  this  variable  is  set,  the value is used to determine the column length for printing
                     select lists.  Select lists will print vertically until about two-thirds of LINES lines are
                     filled.
              MAIL   If  this  variable  is set to the name of a mail file and the MAILPATH variable is not set,
                     then the shell informs the user of arrival of mail in the specified file.
              MAILCHECK
                     This variable specifies how often (in seconds) the shell will  check  for  changes  in  the
                     modification  time  of  any  of the files specified by the MAILPATH or MAIL variables.  The
                     default value is 600 seconds.  When the time  has  elapsed  the  shell  will  check  before
                     issuing the next prompt.
              MAILPATH
                     A  colon  (  :  )  separated  list  of file names.  If this variable is set, then the shell
                     informs the user of any modifications to the specified files that have occurred within  the
                     last  MAILCHECK seconds.  Each file name can be followed by a ?  and a message that will be
                     printed.   The  message  will  undergo  parameter  expansion,  command  substitution,   and
                     arithmetic expansion with the variable $_ defined as the name of the file that has changed.
                     The default message is you have mail in $_.
              PATH   The search path for commands (see Execution below).   The  user  may  not  change  PATH  if
                     executing under rksh (except in .profile).
              PS1    Every  time  a  new  command  line  is  started  on an interactive shell, the value of this
                     variable  is  expanded  to  resolve  backslash  escaping,  parameter   expansion,   command
                     substitution,  and  arithmetic expansion.  The result defines the primary prompt string for
                     that command line.  The default is ``$ ''.  The character !  in the primary  prompt  string
                     is replaced by the command number (see Command Re-entry below).  Two successive occurrences
                     of !  will produce a single !  when the prompt string is printed.  Note that  any  terminal
                     escape  sequences  used  in  the  PS1  prompt  thus need every instance of !  in them to be
                     changed to !!.
              PS2    Secondary prompt string, by default ``> ''.
              PS3    Selection prompt string used within a select loop, by default ``#? ''.
              PS4    The value of this variable is expanded for parameter evaluation, command substitution,  and
                     arithmetic  expansion and precedes each line of an execution trace.  By default, PS4 is ``+
                     ''.  In addition when PS4 is unset, the execution trace prompt is also ``+ ''.
              SHELL  The pathname of the shell is kept in the environment.  At invocation, if  the  basename  of
                     this variable is rsh, rksh, or krsh, then the shell becomes restricted.
              TIMEFORMAT
                     The  value  of  this  parameter  is  used  as  a  format  string  specifying how the timing
                     information for pipelines prefixed with the time reserved word should be displayed.  The  %
                     character  introduces  a  format  sequence  that  is  expanded  to  a  time  value or other
                     information.  The format sequences and their meanings are as follows.
                     %%        A literal %.
                     %[p][l]R  The elapsed time in seconds.
                     %[p][l]U  The number of CPU seconds spent in user mode.
                     %[p][l]S  The number of CPU seconds spent in system mode.
                     %P        The CPU percentage, computed as (U + S) / R.

                     The brackets denote optional portions.  The optional p is a digit specifying the precision,
                     the  number  of  fractional  digits  after a decimal point.  A value of 0 causes no decimal
                     point or fraction to be output.  At most three  places  after  the  decimal  point  can  be
                     displayed; values of p greater than 3 are treated as 3.  If p is not specified, the value 3
                     is used.

                     The optional l specifies a longer format, including hours if greater  than  zero,  minutes,
                     and  seconds  of  the  form  HHhMMmSS.FFs.   The  value  of p determines whether or not the
                     fraction is included.

                     All other characters are output without change and a trailing newline is added.  If  unset,
                     the  default value, $'\nreal\t%2lR\nuser\t%2lU\nsys\t%2lS', is used.  If the value is null,
                     no timing information is displayed.

              TMOUT  Terminal read timeout. If set to a value greater than zero, the read built-in  command  and
                     the select compound command time out after TMOUT seconds when input is from a terminal.  An
                     interactive shell will issue a warning and allow for  an  extra  60  second  timeout  grace
                     period  before terminating if a line is not entered within the prescribed number of seconds
                     while reading from a terminal.  (Note that the shell can be compiled with a  maximum  bound
                     for this value which cannot be exceeded.)

              VISUAL If  the  value  of  this  variable  matches the pattern *[Vv][Ii]*, then the vi option (see
                     Special Command set below) is turned on.  If the value matches the pattern  *gmacs*  ,  the
                     gmacs  option is turned on.  If the value matches the pattern *macs*, then the emacs option
                     will be turned on.  The value of VISUAL overrides the value of EDITOR.

       The shell gives default values to PATH, PS1, PS2, PS3, PS4, MAILCHECK, FCEDIT, TMOUT and IFS, while HOME,
       SHELL, ENV, and MAIL are not set at all by the shell (although HOME is set by login(1)).  On some systems
       MAIL and SHELL are also set by login(1).

   Field Splitting.
       After parameter expansion and command substitution, the results of  substitutions  are  scanned  for  the
       field  separator characters (those found in IFS) and split into distinct fields where such characters are
       found.  Explicit null fields ("" or ′′)  are  retained.   Implicit  null  fields  (those  resulting  from
       parameters that have no values or command substitutions with no output) are removed.

   Brace Expansion.
       If  the  braceexpand  (-B) option is set then each of the fields resulting from IFS are checked to see if
       they contain one or more of the brace patterns {*,*}, {l1..l2} , {n1..n2} , {n1..n2% fmt} , {n1..n2 ..n3}
       ,  or  {n1..n2  ..n3%fmt}  ,  where * represents any character, l1,l2 are letters and n1,n2,n3 are signed
       numbers and fmt is a format specified as used by printf.  In each case, fields are created by  prepending
       the  characters before the { and appending the characters after the } to each of the strings generated by
       the characters between the { and }.  The resulting fields are checked to  see  if  they  have  any  brace
       patterns.

       In the first form, a field is created for each string between { and ,, between , and ,, and between , and
       }.  The string represented by * can contain embedded matching { and } without quoting.  Otherwise, each {
       and } with * must be quoted.

       In  the  seconds form, l1 and l2 must both be either upper case or both be lower case characters in the C
       locale.  In this case a field is created for each character from l1 thru l2.

       In the remaining forms, a field is created for each number starting at n1 and continuing until it reaches
       n2  incrementing  n1 by n3.  The cases where n3 is not specified behave as if n3 where 1 if n1<=n2 and -1
       otherwise.  If forms which specify %fmt any format flags, widths and precisions can be specified and  fmt
       can  end  in  any  of  the  specifiers  cdiouxX.  For example, {a,z}{1..5..3%02d}{b..c}x expands to the 8
       fields, a01bx, a01cx, a04bx, a04cx, z01bx, z01cx, z04bx and z04cx.

   Pathname Expansion.
       This is also known as globbing or sometimes filename generation.   Following  splitting,  each  field  is
       scanned  for the characters *, ?, (, and [ unless the -f option has been set.  If one of these characters
       appears, then the word is regarded as a pattern.  Each file name  component  that  contains  any  pattern
       character  is  replaced  with  a lexicographically sorted set of names that matches the pattern from that
       directory.  If no file name is found that matches the pattern, then that component  of  the  filename  is
       left  unchanged  unless the pattern is prefixed with ∼(N) in which case it is removed as described below.
       The special traversal names .  and ..  are never matched.   If  FIGNORE  is  set,  then  each  file  name
       component  that  matches  the  pattern  defined  by  the  value of FIGNORE is ignored when generating the
       matching filenames.  If FIGNORE is not set, the character .  at the start of  each  file  name  component
       will  be  ignored  unless  the  first  character  of  the  pattern corresponding to this component is the
       character .  itself.  Note, that for other uses of  pattern  matching  the  /  and  .   are  not  treated
       specially.

              *      Matches  any  string,  including the null string.  When used for filename expansion, if the
                     globstar option is on, an isolated pattern of two adjacent *'s will  match  all  files  and
                     zero  or more directories and subdirectories.  If followed by a / then only directories and
                     subdirectories will match.
              ?      Matches any single character.
              [...]  Matches any one of the enclosed characters.  A pair of characters separated  by  -  matches
                     any  character lexically between the pair, inclusive.  If the first character following the
                     opening [ is a !  or ^ then any character not enclosed is matched.  A - can be included  in
                     the character set by putting it as the first or last character.
                     Within [ and ], character classes can be specified with the syntax [:class:] where class is
                     one of the following classes defined in the ANSI C standard: (Note that word is  equivalent
                     to alnum plus the character _.)
                     alnum alpha blank cntrl digit graph lower print punct space upper word xdigit
                     Within  [  and ], an equivalence class can be specified with the syntax [=c=] which matches
                     all characters with the same primary collation weight (as defined by the current locale) as
                     the character c.  Within [ and ], [.symbol.]  matches the collating symbol symbol.
       A  pattern-list is a list of one or more patterns separated from each other with a & or |.  A & signifies
       that all patterns must be matched whereas |  requires  that  only  one  pattern  be  matched.   Composite
       patterns can be formed with one or more of the following subpatterns:
              ?(pattern-list)
                     Optionally matches any one of the given patterns.
              *(pattern-list)
                     Matches zero or more occurrences of the given patterns.
              +(pattern-list)
                     Matches one or more occurrences of the given patterns.
              {n}(pattern-list)
                     Matches n occurrences of the given patterns.
              {m,n}(pattern-list)
                     Matches  from  m  to n occurrences of the given patterns.  If m is omitted, 0 will be used.
                     If n is omitted at least m occurrences will be matched.
              @(pattern-list)
                     Matches exactly one of the given patterns.
              !(pattern-list)
                     Matches anything except one of the given patterns.
       By default, each pattern, or subpattern will match the longest string possible consistent with generating
       the longest overall match.  If more than one match is possible, the one starting closest to the beginning
       of the string will be chosen.   However, for each of the above compound patterns a - can be  inserted  in
       front of the ( to cause the shortest match to the specified pattern-list to be used.

       When  pattern-list  is  contained within parentheses, the backslash character \ is treated specially even
       when inside a character class.   All ANSI C character escapes are  recognized  and  match  the  specified
       character.  In addition the following escape sequences are recognized:
              \d     Matches any character in the digit class.
              \D     Matches any character not in the digit class.
              \s     Matches any character in the space class.
              \S     Matches any character not in the space class.
              \w     Matches any character in the word class.
              \W     Matches any character not in the word class.

       A  pattern  of  the  form  %(pattern-pair(s))  is a subpattern that can be used to match nested character
       expressions.  Each pattern-pair is a two character sequence which cannot  contain  &  or  |.   The  first
       pattern-pair  specifies  the  starting and ending characters for the match.  Each subsequent pattern-pair
       represents the beginning and ending characters of a nested group that will be skipped over when  counting
       starting  and  ending  character  matches.   The  behavior  is  unspecified when the first character of a
       pattern-pair is alphanumeric except for the following:
              D      Causes the ending character to terminate the search for  this  pattern  without  finding  a
                     match.
              E      Causes the ending character to be interpreted as an escape character.
              L      Causes  the  ending character to be interpreted as a quote character causing all characters
                     to be ignored when looking for a match.
              Q      Causes the ending character to be interpreted as a quote character causing  all  characters
                     other than any escape character to be ignored when looking for a match.
       Thus,  %({}Q"E\),  matches characters starting at { until the matching } is found not counting any { or }
       that is inside a double quoted string or preceded by the escape character \.  Without the {} this pattern
       matches any C language string.

       Each  subpattern  in  a composite pattern is numbered, starting at 1, by the location of the ( within the
       pattern.  The sequence \n, where n is a single digit and \n comes after the n-th. subpattern, matches the
       same string as the subpattern itself.

       Finally  a  pattern  can contain subpatterns of the form ∼(options:pattern-list), where either options or
       :pattern-list can be omitted.  Unlike the other compound patterns, these subpatterns are not  counted  in
       the  numbered  subpatterns.  :pattern-list must be omitted for options F, G, N , and V below.  If options
       is present, it can consist of one or more of the following:
              +      Enable the following options.  This is the default.
              -      Disable the following options.
              E      The remainder of the pattern uses extended regular  expression  syntax  like  the  egrep(1)
                     command.
              F      The remainder of the pattern uses fgrep(1) expression syntax.
              G      The remainder of the pattern uses basic regular expression syntax like the grep(1) command.
              K      The remainder of the pattern uses shell pattern syntax.  This is the default.
              N      This is ignored.  However, when it is the first letter and is used with pathname expansion,
                     and no matches occur, the file pattern expands to the empty string.
              X      The remainder of the pattern uses augmented regular expression  syntax  like  the  xgrep(1)
                     command.
              P      The  remainder of the pattern uses perl(1) regular expression syntax.  Not all perl regular
                     expression syntax is currently implemented.
              V      The remainder of the pattern uses System V regular expression syntax.
              i      Always treat the match as case-insensitive, regardless of the globcasedetect shell option.
              g      File the longest match (greedy).  This is the default.
              l      Left anchor the pattern.  This is the default for K style patterns.
              r      Right anchor the pattern.  This is the default for K style patterns.
       If both options  and  :pattern-list  are  specified,  then  the  options  apply  only  to   pattern-list.
       Otherwise, these options remain in effect until they are disabled by a subsequent ∼(...) or at the end of
       the subpattern containing ∼(...).

   Quoting.
       Each of the metacharacters listed earlier (see Definitions above) has a special meaning to the shell  and
       causes  termination  of a word unless quoted.  A character may be quoted (i.e., made to stand for itself)
       by preceding it with a \.  The pair \new-line is removed.  All characters  enclosed  between  a  pair  of
       single  quote marks (′′) that is not preceded by a $ are quoted.  A single quote cannot appear within the
       single quotes.  A single quoted string preceded by an unquoted $ is processed as an ANSI C string  except
       for the following:
       \0     Causes the remainder of the string to be ignored.
       \E     Equivalent to the escape character (ASCII 033),
       \e     Equivalent to the escape character (ASCII 033),
       \cx    Expands to the character control-x.
       \C[.name.]
              Expands to the collating element name.

       Inside  double  quote marks (""), parameter and command substitution occur and \ quotes the characters \,
       `, ", and $.  A $ in front of a double quoted string will be ignored in the "C" or  "POSIX"  locale,  and
       may  cause  the string to be replaced by a locale specific string otherwise.  The meaning of $* and $@ is
       identical when not quoted or when used as a variable assignment value or as a file name.   However,  when
       used  as a command argument, "$*" is equivalent to "$1d$2d...", where d is the first character of the IFS
       variable, whereas "$@" is equivalent to "$1" "$2" ....  Inside grave  quote  marks  (``),  \  quotes  the
       characters \, `, and $.  If the grave quotes occur within double quotes, then \ also quotes the character
       ".

       The special meaning of reserved words or aliases can be removed by quoting any character of the  reserved
       word.   The  recognition  of  function  names or built-in command names listed below cannot be altered by
       quoting them.

   Arithmetic Evaluation.
       The shell performs arithmetic evaluation for arithmetic expansion, to evaluate an arithmetic command,  to
       evaluate  an indexed array subscript, and to evaluate arguments to the built-in commands shift and let as
       well as arguments to numeric format specifiers given to print -f  and printf.  Evaluations are  performed
       using double precision floating point arithmetic or long double precision floating point for systems that
       provide this data type.  Floating point constants follow the ANSI C programming language  floating  point
       conventions.   The  case-insensitive floating point constants NaN and Inf can be used to represent "not a
       number" and infinity respectively, unless the posix shell option is on.   Integer  constants  follow  the
       ANSI  C  programming  language integer constant conventions although only single byte character constants
       are recognized and character casts are not recognized.  In addition constants can be of the form [base#]n
       where  base  is  a  decimal number between two and sixty-four representing the arithmetic base and n is a
       number in that base.  The digits above 9 are represented by  the  lower  case  letters,  the  upper  case
       letters,  @, and _ respectively.  For bases less than or equal to 36, upper and lower case characters can
       be used interchangeably.

       An arithmetic expression uses the same syntax, precedence, and  associativity  of  expression  as  the  C
       language.   All  the  C  language  operators  that  apply  to  floating point quantities can be used.  In
       addition, the operator ** can be used for exponentiation.  It has higher precedence  than  multiplication
       and  is  left associative.  In addition, when the value of an arithmetic variable or subexpression can be
       represented as a long integer, all C language integer arithmetic operations can be performed.   Variables
       can  be  referenced by name within an arithmetic expression without using the parameter expansion syntax.
       When a variable is referenced, its value is evaluated as an arithmetic expression.

       Any of the following math library functions that are in  the  C  math  library  can  be  used  within  an
       arithmetic expression:

       abs acos acosh asin asinh atan atan2 atanh cbrt ceil copysign cos cosh erf erfc exp exp10 exp2 expm1 fabs
       fdim finite float floor fma fmax  fmin  fmod  fpclass  fpclassify  hypot  ilogb  int  isfinite  isgreater
       isgreaterequal  isinf  isinfinite isless islessequal islessgreater isnan isnormal issubnormal isunordered
       iszero j0 j1 jn ldexp lgamma log log10 log1p log2 logb nearbyint nextafter nexttoward pow remainder  rint
       round scalb scalbn signbit sin sinh sqrt tan tanh tgamma trunc y0 y1 yn

       In  addition,  arithmetic functions can be defined as shell functions with a variant of the function name
       syntax,

       function .sh.math.name ident ... { list ;}
              where name is the function name used in the arithmetic expression and each identifier, ident is  a
              name  reference to the long double precision floating point argument.  The value of .sh.value when
              the function returns is the value of this function.  User defined  functions  can  take  up  to  3
              arguments and override C math library functions.

       An  internal  representation of a variable as a double precision floating point can be specified with the
       -E [n], -F [n], or -X [n] option of the typeset special built-in  command.   The  -E  option  causes  the
       expansion  of  the  value  to be represented using scientific notation when it is expanded.  The optional
       option argument n defines the number of significant figures.  The -F option causes the  expansion  to  be
       represented  as  a floating decimal number when it is expanded.  The -X option causes the expansion to be
       represented using the %a format defined by ISO C-99.  The optional option argument n defines  the  number
       of places after the decimal (or radix) point in this case.

       An  internal  integer representation of a variable can be specified with the -i [n] option of the typeset
       special built-in command.  The optional option argument n specifies an arithmetic base to  be  used  when
       expanding the variable.  If you do not specify an arithmetic base, base 10 will be used.

       Arithmetic  evaluation is performed on the value of each assignment to a variable with the -E, -F, -X, or
       -i attribute.  Assigning a floating point number to a variable  whose  type  is  an  integer  causes  the
       fractional part to be truncated.

   Prompting.
       When  used  interactively,  the  shell  prompts  with  the  value of PS1 after expanding it for parameter
       expansion, command substitution, and arithmetic expansion, before reading a command.  In  addition,  each
       single  !  in the prompt is replaced by the command number.  A !!  is required to place !  in the prompt.
       If at any time a new-line is typed and further input is needed to complete a command, then the  secondary
       prompt (i.e., the value of PS2) is issued.

   Conditional Expressions.
       A  conditional expression is used with the [[ compound command to test attributes of files and to compare
       strings.  Field splitting and pathname expansion are not performed on the words between [[ and ]].   Each
       expression can be constructed from one or more of the following unary or binary expressions:
       string True, if string is not null.
       -a file
              Same as -e below.  This is obsolete.
       -b file
              True, if file exists and is a block special file.
       -c file
              True, if file exists and is a character special file.
       -d file
              True, if file exists and is a directory.
       -e file
              True, if file exists.
       -f file
              True, if file exists and is an ordinary file.
       -g file
              True, if file exists and it has its setgid bit set.
       -k file
              True, if file exists and it has its sticky bit set.
       -n string
              True, if length of string is non-zero.
       -o ?option
              True, if option named option is a valid option name.
       -o option
              True, if option named option is on.
       -p file
              True, if file exists and is a fifo special file or a pipe.
       -r file
              True, if file exists and is readable by current process.
       -s file
              True, if file exists and has size greater than zero.
       -t fildes
              True, if file descriptor number fildes is open and associated with a terminal device.
       -u file
              True, if file exists and it has its setuid bit set.
       -v name
              True, if variable name is a valid variable name and is set.
       -w file
              True, if file exists and is writable by current process.
       -x file
              True,  if  file  exists  and is executable by current process.  If file exists and is a directory,
              then true if the current process has permission to search in the directory.
       -z string
              True, if length of string is zero.
       -L file
              True, if file exists and is a symbolic link.
       -h file
              True, if file exists and is a symbolic link.
       -N file
              True, if file exists and the modification time is greater than the last access time.
       -O file
              True, if file exists and is owned by the effective user id of this process.
       -G file
              True, if file exists and its group matches the effective group id of this process.
       -R name
              True if variable name is a name reference.
       -S file
              True, if file exists and is a socket.
       file1 -nt file2
              True, if file1 exists and file2 does not, or file1 is newer than file2.
       file1 -ot file2
              True, if file2 exists and file1 does not, or file1 is older than file2.
       file1 -ef file2
              True, if file1 and file2 exist and refer to the same file.
       string == pattern
              True, if string matches pattern.  Any part of pattern can be quoted to cause it to be matched as a
              string.  With a successful match to a pattern, the .sh.match array variable will contain the match
              and subpattern matches.
       string = pattern
              Same as == above, but is obsolete.
       string != pattern
              True, if string does not match pattern.  When the string matches the pattern the  .sh.match  array
              variable will contain the match and subpattern matches.
       string =∼ ere
              True if string matches the pattern ∼(E)ere where ere is an extended regular expression.
       string1 < string2
              True, if string1 comes before string2 based on ASCII value of their characters.
       string1 > string2
              True, if string1 comes after string2 based on ASCII value of their characters.
       The following obsolete arithmetic comparisons are also permitted:
       exp1 -eq exp2
              True, if exp1 is equal to exp2.
       exp1 -ne exp2
              True, if exp1 is not equal to exp2.
       exp1 -lt exp2
              True, if exp1 is less than exp2.
       exp1 -gt exp2
              True, if exp1 is greater than exp2.
       exp1 -le exp2
              True, if exp1 is less than or equal to exp2.
       exp1 -ge exp2
              True, if exp1 is greater than or equal to exp2.

       In  each of the above expressions, if file is of the form /dev/fd/n, where n is an integer, then the test
       is applied to the open file whose descriptor number is n.

       A compound expression can be constructed from these primitives by using any of the following,  listed  in
       decreasing order of precedence.
       (expression)
              True, if expression is true.  Used to group expressions.
       ! expression
              True if expression is false.
       expression1 && expression2
              True, if expression1 and expression2 are both true.
       expression1 || expression2
              True, if either expression1 or expression2 is true.

   Input/Output.
       Before a command is executed, its input and output may be redirected using a special notation interpreted
       by the shell.  The following may appear anywhere in a simple-command or may precede or follow  a  command
       and  are not passed on to the invoked command.  Command substitution, parameter expansion, and arithmetic
       expansion occur before word or digit is used except as noted below.  Pathname expansion  occurs  only  if
       the shell is interactive and the pattern matches a single file.  Field splitting is not performed.

       In each of the following redirections, if file is of the form /dev/sctp/host/port, /dev/tcp/host/port, or
       /dev/udp/host/port, where host is a hostname or host address, and port is a service given by name  or  an
       integer  port  number,  then  the  redirection  attempts  to  make  a  tcp, sctp or udp connection to the
       corresponding socket.

       No intervening space is allowed between the characters of redirection operators.

       <word         Use file word as standard input (file descriptor 0).

       >word         Use file word as standard output (file descriptor 1).  If the file does not exist  then  it
                     is  created.   If  the  file  exists, and the noclobber option is on, this causes an error;
                     otherwise, it is truncated to zero length.

       >|word        Same as >, except that it overrides the noclobber option.

       >;word        Write output to a temporary file.  If the command completes successfully rename it to word,
                     otherwise,  delete  the  temporary  file.  >;word cannot be used with the exec and redirect
                     built-ins.

       >>word        Use file word as standard output.  If the file exists, then output is appended  to  it  (by
                     first seeking to the end-of-file); otherwise, the file is created.

       <>word        Open  file word for reading and writing as standard output.  If the posix option is active,
                     it defaults to standard input instead.

       <>;word       The same as <>word except that if the command completes successfully, word is truncated  to
                     the offset at command completion.  <>;word cannot be used with the exec and redirect built-
                     ins.

       <<[-]word     The shell input is read up to a line that is the same as word after any  quoting  has  been
                     removed,  or  to  an end-of-file.  No parameter expansion, command substitution, arithmetic
                     expansion or pathname expansion is performed on word.  The  resulting  document,  called  a
                     here-document,  becomes  the  standard  input.  If any character of word is quoted, then no
                     interpretation is  placed  upon  the  characters  of  the  document;  otherwise,  parameter
                     expansion,  command substitution, and arithmetic expansion occur, \new-line is ignored, and
                     \ must be used to quote the characters \, $, `.  If - is appended to <<, then  all  leading
                     tabs  are  stripped  from word and from the document.  If # is appended to <<, then leading
                     spaces and tabs will be stripped off the first line of the document and up to an equivalent
                     indentation will be stripped from the remaining lines and from word.  A tab stop is assumed
                     to occur at every 8 columns for the purposes of determining the indentation.

       <<<word       A short form of here document in which word becomes the contents of the here-document after
                     any parameter expansion, command substitution, and arithmetic expansion occur.

       <&digit       The standard input is duplicated from file descriptor digit (see dup(2)).

       >&digit       The standard output is duplicated from file descriptor digit.

       <&digit-      The file descriptor given by digit is moved to standard input.

       >&digit-      The file descriptor given by digit is moved to standard output.

       <&-           The standard input is closed.

       >&-           The standard output is closed.

       <&p           The input from the co-process is moved to standard input.

       >&p           The output to the co-process is moved to standard output.

       <#((expr))    Evaluate  arithmetic  expression expr and position file descriptor 0 to the resulting value
                     bytes from the start of the file.  The variables CUR and EOF evaluate to the current offset
                     and end-of-file offset respectively when evaluating expr.

       >#((offset))  The same as <# except applies to file descriptor 1.

       <#pattern     Seeks forward to the beginning of the next line containing pattern.

       <##pattern    The  same  as  <# except that the portion of the file that is skipped is copied to standard
                     output.

       If one of the above is preceded by a digit, with no intervening space, then the  file  descriptor  number
       referred  to  is that specified by the digit (instead of the default 0 or 1).  If one of the above, other
       than >&- and the ># and <# forms, is preceded by  {varname}  with  no  intervening  space,  then  a  file
       descriptor number > 9 will be selected by the shell and stored in the variable varname, so it can be read
       from or written to with redirections like <& $varname or >& $varname.  If >&- or the any of the ># and <#
       forms  is  preceded  by  {varname} the value of varname defines the file descriptor to close or position.
       For example:

              ... 2>&1

       means file descriptor 2 is to be opened for writing as a duplicate of file descriptor 1 and

              exec {n}<file

       means open file named file for reading and store the file descriptor number in variable n.

       A special shorthand redirection operator &>word is available; it is equivalent to >word 2>&1.  It  cannot
       be  preceded  by  any  digit  or  variable  name. This shorthand is disabled if the posix shell option is
       active.

       The order in which redirections are specified is significant.  The shell evaluates  each  redirection  in
       terms of the (file descriptor, file) association at the time of evaluation.  For example:

              ... 1>fname 2>&1

       first  associates  file descriptor 1 with file fname.  It then associates file descriptor 2 with the file
       associated with file descriptor 1 (i.e.  fname).  If  the  order  of  redirections  were  reversed,  file
       descriptor  2  would  be associated with the terminal (assuming file descriptor 1 had been) and then file
       descriptor 1 would be associated with file fname.

       If a command is followed by & and job control is not active, then the  default  standard  input  for  the
       command  is the empty file /dev/null.  Otherwise, the environment for the execution of a command contains
       the file descriptors of the invoking shell as modified by input/output specifications.

   Environment.
       The environment (see environ(7)) is a list of name-value pairs that is passed to an executed  program  in
       the  same  way  as  a  normal  argument list.  The names must be identifiers and the values are character
       strings.  The shell interacts with the environment in several ways.  On invocation, the shell  scans  the
       environment  and creates a variable for each name found, giving it the corresponding value and attributes
       and marking it export.  Executed commands inherit the environment.  If the user modifies  the  values  of
       these  variables  or  creates  new ones, using the export or typeset -x commands, they become part of the
       environment.  The environment seen by any executed command is  thus  composed  of  any  name-value  pairs
       originally  inherited by the shell, whose values may be modified by the current shell, plus any additions
       which must be noted in export or typeset -x commands.

       The environment for any simple-command or function may be augmented by prefixing  it  with  one  or  more
       variable assignments.  A variable assignment argument is a word of the form identifier=value.  Thus:

              TERM=450 cmd args                  and
              (export TERM; TERM=450; cmd args)

       are  equivalent  (as  far as the above execution of cmd is concerned except for special built-in commands
       listed below - those that are marked with ).

       If the obsolete -k option is set, all variable assignment arguments are placed in the  environment,  even
       if they occur after the command name.  The following first prints a=b c and then c:

              echo a=b c
              set -k
              echo a=b c
       This  feature is intended for use with scripts written for early versions of the shell and its use in new
       scripts is strongly discouraged.  It is likely to disappear someday.

   Functions.
       For historical reasons, there are two ways to define functions, the name() syntax and the  function  name
       syntax,  described  in  the  Commands  section above.  Shell functions are read in and stored internally.
       Alias names are resolved when the function is read.   Functions  are  executed  like  commands  with  the
       arguments passed as positional parameters.  (See Execution below.)

       Functions  defined  by  the  function  name  syntax and called by name execute in the same process as the
       caller and share all files and present working directory with the caller.  Traps caught by the caller are
       reset to their default action inside the function.  A trap condition that is not caught or ignored by the
       function causes the function to terminate and the condition to be passed on to the  caller.   A  trap  on
       EXIT  set  inside  a  function is executed in the environment of the caller after the function completes.
       Ordinarily, variables are shared between the calling program and  the  function.   However,  the  typeset
       special  built-in command used within a function defines local variables whose scope includes the current
       function.  They can be passed to functions that they call in the variable assignment list  that  precedes
       the  call  or  as  arguments  passed  as  name references.  Errors within functions return control to the
       caller.

       Functions defined with the name() syntax and functions defined with the function  name  syntax  that  are
       invoked with the .  special built-in are executed in the caller's environment and share all variables and
       traps with the caller.  Errors within these function executions cause the script that  contains  them  to
       abort.

       The special built-in command return is used to return from function calls.

       Function  names can be listed with the -f or +f option of the typeset special built-in command.  The text
       of functions, when available, will also be listed with -f.  Functions can be undefined with the -f option
       of the unset special built-in command.

       Ordinarily,  functions  are  unset  when  the  shell  executes a shell script.  Functions that need to be
       defined across separate invocations of the shell should be placed in a directory and the  FPATH  variable
       should contain the name of this directory.  They may also be specified in the ENV file.

   Discipline Functions.
       Each  variable  can  have  zero  or  more  discipline  functions associated with it.  The shell initially
       understands the discipline names get, set, append, and unset but can be added when  defining  new  types.
       On most systems others can be added at run time via the C programming interface extension provided by the
       builtin built-in utility.  If the get discipline is defined for a variable, it is  invoked  whenever  the
       given  variable  is  referenced.   If  the  variable  .sh.value is assigned a value inside the discipline
       function, the referenced variable will evaluate to this value instead.  If the set discipline is  defined
       for  a variable, it is invoked whenever the given variable is assigned a value.  If the append discipline
       is defined for a variable, it is invoked whenever a  value  is  appended  to  the  given  variable.   The
       variable  .sh.value  is  given the value of the variable before invoking the discipline, and the variable
       will be assigned the value of .sh.value after the discipline completes.  If .sh.value is unset inside the
       discipline,  then  that  value  is  unchanged.   If the unset discipline is defined for a variable, it is
       invoked whenever the given variable is unset.  The  variable  will  not  be  unset  unless  it  is  unset
       explicitly from within this discipline function.

       The  variable  .sh.name  contains  the  name of the variable for which the discipline function is called,
       .sh.subscript is the subscript of the variable, and .sh.value  will  contain  the  value  being  assigned
       inside  the  set  discipline  function.   The  variable  _  is  a reference to the variable including the
       subscript if any.  For the set discipline, changing .sh.value will change the value that  gets  assigned.
       Finally,  the  expansion  ${var.name}, when name is the name of a discipline, and there is no variable of
       this name, is equivalent to the command substitution ${ var.name;}.

   Name Spaces.
       Commands and functions that are executed as part of the list of a namespace command that modify variables
       or create new ones, create a new variable whose name is the name of the name space as given by identifier
       preceded by ..  When a variable whose name is  name  is  referenced,  it  is  first  searched  for  using
       .identifier.name.   Similarly, a function defined by a command in the namespace list is created using the
       name space name preceded by a ..

       When  the list of a namespace command contains a namespace command, the names of variables and  functions
       that  are  created  consist  of  the  variable  or function name preceded by the list of identifiers each
       preceded by ..

       Outside of a name space, a variable or function  created  inside  a  name  space  can  be  referenced  by
       preceding it with the name space name.

       By default, variables starting with .sh are in the sh name space.

   Type Variables.
       Typed  variables  provide  a way to create data structure and objects.  A type can be defined either by a
       shared library, by the enum built-in command described below, or by  using  the  new  -T  option  of  the
       typeset  built-in command.  With the -T option of typeset, the type name, specified as an option argument
       to -T, is set with a compound variable assignment that defines the type.  Function definitions can appear
       inside  the  compound  variable assignment and these become discipline functions for this type and can be
       invoked or redefined by each instance of the type.  The function name create is treated specially.  It is
       invoked  for  each  instance of the type that is created but is not inherited and cannot be redefined for
       each instance.

       When a type is defined a special built-in command of that name is added.  These built-ins are declaration
       commands  and  follow  the  same expansion rules as the built-in commands described below that are marked
       with a ‡ symbol. These commands can subsequently be used inside further type definitions.  The  man  page
       for  these  commands  can be generated by using the --man option or any of the other -- options described
       with getopts.  The -r, -a, -A, -h, and -S options of typeset are permitted with each of these new  built-
       ins.

       An  instance of a type is created by invoking the type name followed by one or more instance names.  Each
       instance of the type is initialized with a copy of the subvariables  except  for  subvariables  that  are
       defined with the -S option.  Variables defined with the -S are shared by all instances of the type.  Each
       instance can change the value of any subvariable and can also define new discipline functions of the same
       names  as  those  defined by the type definition as well as any standard discipline names.  No additional
       subvariables can be defined for any instance.

       When defining a type, if the value of a subvariable is not set and the  -r  attribute  is  specified,  it
       causes  the  subvariable  to  be  a required subvariable.  Whenever an instance of a type is created, all
       required subvariables must be specified.  These subvariables become read-only in each instance.

       When unset is invoked on a subvariable within a type, and the -r attribute has  not  been  specified  for
       this  field, the value is reset to the default value associative with the type.  Invoking unset on a type
       instance not contained within another type deletes all subvariables and the variable itself.

       A type definition can be derived from another type definition by defining the first subvariable name as _
       and  defining  its  type as the base type.  Any remaining definitions will be additions and modifications
       that apply to the new type.  If the new type name is the same as that of the base type, the type will  be
       replaced and the original type will no longer be accessible.

       The typeset command with the -T and no option argument or operands will write all the type definitions to
       standard output in a form that can be read in to create all they types.

   Jobs.
       If the monitor option of the set command is turned on, an interactive shell associates a  job  with  each
       pipeline.   It keeps a table of current jobs, printed by the jobs command, and assigns them small integer
       numbers.  When a job is started asynchronously with &, the shell prints a line which looks like:

            [1] 1234

       indicating that the job which was started asynchronously  was  job  number  1  and  had  one  (top-level)
       process, whose process id was 1234.

       This  paragraph and the next require features that are not in all versions of UNIX and may not apply.  If
       you are running a job and wish to do something else you may hit the key ^Z (control-Z) which sends a STOP
       signal  to  the  current job.  The shell will then normally indicate that the job has been `Stopped', and
       print another prompt.  You can then manipulate the state of this job, putting it in the  background  with
       the  bg  command,  or  run some other commands and then eventually bring the job back into the foreground
       with the foreground command fg.  A ^Z takes effect immediately and is like an interrupt in  that  pending
       output and unread input are discarded when it is typed.

       A  job  being run in the background will stop if it tries to read from the terminal.  Background jobs are
       normally allowed to produce output, but this can be disabled by giving the command stty tostop.   If  you
       set  this  tty  option,  then background jobs will stop when they try to produce output like they do when
       they try to read input.

       A job pool is a collection of jobs started with list & associated with a name.

       There are several ways to refer to jobs in the shell.  A job can be referred to by the process id of  any
       process of the job or by one of the following:
       %number
              The job with the given number.
       pool   All the jobs in the job pool named by pool.
       pool.number
              The job number number in the job pool named by pool.
       %string
              Any job whose command line begins with string.
       %?string
              Any job whose command line contains string.
       %%     Current job.
       %+     Equivalent to %%.
       %-     Previous job.  In addition, unless noted otherwise, wherever a job can be specified, the name of a
              background job pool can be used to represent all the jobs in that pool.

       The shell learns immediately whenever a process changes state.  It normally informs you  whenever  a  job
       becomes  blocked  so that no further progress is possible, but only just before it prints a prompt.  This
       is done so that it does not otherwise disturb your work.  The notify option of the set command causes the
       shell to print these job change messages as soon as they occur.

       When the monitor option is on, each background job that completes triggers any trap set for CHLD.

       When  you  try  to  leave  the shell while jobs are running or stopped, you will be warned that `You have
       stopped(running) jobs.'  You may use the jobs command to see what they are.  If you  immediately  try  to
       exit  again,  the shell will not warn you a second time, and the stopped jobs will be terminated.  When a
       login shell receives a HUP signal, it sends a HUP signal to each job that has not been disowned with  the
       disown built-in command described below.

   Signals.
       The  INT  and  QUIT  signals  for  an invoked command are ignored if the command is followed by & and the
       monitor option is not active.  Otherwise, signals have the values inherited by the shell from its  parent
       (but see also the trap built-in command below).

   Execution.
       Each time a command is read, the above expansions and substitutions are carried out.  If the command name
       matches one of the Special Built-in Commands listed below,  it  is  executed  within  the  current  shell
       process.   Next,  the  command name is checked to see if it matches a user defined function.  If it does,
       the positional parameters are saved and then reset to the arguments of the function call.  A function  is
       also  executed  in  the  current  shell  process.   When  the  function completes or issues a return, the
       positional parameter list is restored.  For functions defined with the function name syntax, any trap set
       on  EXIT  within the function is executed.  The exit value of a function is the value of the last command
       executed.  If a command name is not a special built-in command or a user defined function, but it is  one
       of the built-in commands listed below, it is executed in the current shell process.

       The shell variables PATH followed by the variable FPATH defines the list of directories to search for the
       command name.  Alternative directory names are separated by a colon (:).  The default path is  the  value
       that  was output by getconf PATH at the time ksh was compiled.  The current directory can be specified by
       two or more adjacent colons, or by a colon at the beginning or end of the path list.  If the command name
       contains  a  /,  then  the search path is not used.  Otherwise, each directory in the list of directories
       defined by PATH and FPATH is checked in order.  If the directory being searched is contained in FPATH and
       contains  a file whose name matches the command being searched, then this file is loaded into the current
       shell environment as if it were the argument to the  .  command  except  that  only  preset  aliases  are
       expanded, and a function of the given name is executed as described above.

       If  this  directory  is  not in FPATH the shell first determines whether there is a built-in version of a
       command corresponding to a given pathname and if so it is invoked in the current process.  If no built-in
       is  found,  the  shell checks for a file named .paths in this directory.  If found and there is a line of
       the form FPATH=path where path names an existing directory then that directory  is  searched  immediately
       after the current directory as if it were found in the FPATH variable.  If path does not begin with /, it
       is checked for relative to the directory being searched.

       The .paths file is then checked for a line of the form PLUGIN_LIB=libname [  :  libname  ]  ...  .   Each
       library  named  by libname will be searched for as if it were an option argument to builtin -f, and if it
       contains a built-in of the specified name this will be executed instead of a command by this  name.   Any
       built-in loaded from a library found this way will be associated with the directory containing the .paths
       file so it will only execute if not found in an earlier directory.

       Finally, the directory will be checked for a file of the given name.  If the file has execute  permission
       but  is  not  an  a.out  file, it is assumed to be a file containing shell commands.  A separate shell is
       spawned to read it.  All non-exported variables are removed in this case.   If  the  shell  command  file
       doesn't  have  read  permission,  or if the setuid and/or setgid bits are set on the file, then the shell
       executes an agent whose job it is to set up the permissions and execute the shell with the shell  command
       file  passed  down as an open file.  If the .paths contains a line of the form name=value in the first or
       second line, then the environment variable name is modified by  prepending  the  directory  specified  by
       value  to  the  directory  list.   If  value  is not an absolute directory, then it specifies a directory
       relative to the directory that the executable was found.  If  the  environment  variable  name  does  not
       already  exist  it  will  be  added  to  the environment list for the specified command.  A parenthesized
       command is executed in a subshell without removing non-exported variables.

   Command Re-entry.
       The text of the last HISTSIZE (default 512) commands entered from a terminal device is saved in a history
       file.   The file $HOME/.sh_history is used if the HISTFILE variable is not set or if the file it names is
       not writable.  A shell can access the commands of  all  interactive  shells  which  use  the  same  named
       HISTFILE.   The built-in command hist is used to list or edit a portion of this file.  The portion of the
       file to be edited or listed can be selected by number or by giving the first character or  characters  of
       the  command.   A  single command or range of commands can be specified.  If you do not specify an editor
       program as an argument to hist then the value of the variable HISTEDIT is used.  If  HISTEDIT  is  unset,
       the  obsolete  variable  FCEDIT  is  used.   If  FCEDIT is not defined, then /bin/ed is used.  The edited
       command(s) is printed and re-executed upon leaving the editor unless you quit without  writing.   The  -s
       option  (and in obsolete versions, the editor name -) is used to skip the editing phase and to re-execute
       the command.  In this case a substitution parameter of the form old=new can be used to modify the command
       before  execution.   For  example,  with  the  preset  alias  r, which is aliased to ′hist -s′, typing `r
       bad=good c' will re-execute the most recent command which starts with the letter c, replacing  the  first
       occurrence of the string bad with the string good.

   In-line Editing Options.
       Normally,  each  command  line  entered  from  a  terminal  device is simply typed followed by a new-line
       (`RETURN' or `LINE FEED').  If either the emacs, gmacs, or vi option is active, the  user  can  edit  the
       command  line.   To  be in either of these edit modes set the corresponding option.  An editing option is
       automatically selected each time the VISUAL or EDITOR variable is assigned a value ending  in  either  of
       these option names.

       The  editing  features  require  that the user's terminal accept `RETURN' as carriage return without line
       feed and that a space (` ') must overwrite the current character on the screen.

       Unless the multiline option is on, the editing modes implement  a  concept  where  the  user  is  looking
       through  a  window  at  the  current  line.   The  window width is the value of COLUMNS if it is defined,
       otherwise 80.  If the window width is too small to display the prompt and leave at  least  8  columns  to
       enter  input,  the  prompt is truncated from the left.  If the line is longer than the window width minus
       two, a mark is displayed at the end of the window to notify the user.  As the cursor  moves  and  reaches
       the  window  boundaries the window will be centered about the cursor.  The mark is a > (<, *) if the line
       extends on the right (left, both) side(s) of the window.

       The search commands in each edit mode provide access to the history file.  Only strings are matched,  not
       patterns,  although  a leading ^ in the string restricts the match to begin at the first character in the
       line.

       Each of the edit modes has an operation to list the files or commands  that  match  a  partially  entered
       word.   When applied to the first word on the line, or the first word after a ;, |, &, or (, and the word
       does not begin with  or contain a /, the list of aliases, functions, and executable commands defined  by
       the  PATH  variable  that  could  match the partial word is displayed.  Otherwise, the list of files that
       match the given word is displayed.  If the partially entered word does not  contain  any  file  expansion
       characters,  a  *  is  appended  before generating these lists.  After displaying the generated list, the
       input line is redrawn.  These  operations  are  called  command  name  listing  and  file  name  listing,
       respectively.   There  are  additional  operations,  referred to as command name completion and file name
       completion, which compute the list of matching commands or files,  but  instead  of  printing  the  list,
       replace  the  current  word  with a complete or partial match.  For file name completion, if the match is
       unique, a / is appended if the file is a directory and  a  space  is  appended  if  the  file  is  not  a
       directory.   Otherwise,  the  longest  common  prefix  for all the matching files replaces the word.  For
       command name completion, only the portion of the file names after the last / are used to find the longest
       command  prefix.   If  only a single name matches this prefix, then the word is replaced with the command
       name followed by a space.  When using a tab for  completion  that  does  not  yield  a  unique  match,  a
       subsequent  tab  will provide a numbered list of matching alternatives.  A specific selection can be made
       by entering the selection number followed by a tab.

   Key Bindings.
       The KEYBD trap can be used to intercept keys as they  are  typed  and  change  the  characters  that  are
       actually  seen  by the shell.  This trap is executed after each character (or sequence of characters when
       the first character is ESC) is entered while reading from a terminal.  The variable  .sh.edchar  contains
       the  character  or  character sequence which generated the trap.  Changing the value of .sh.edchar in the
       trap action causes the shell to behave as if the new value were entered from the keyboard rather than the
       original value.

       The  variable  .sh.edcol  is  set to the input column number of the cursor at the time of the input.  The
       variable .sh.edmode is set to ESC when in  vi  insert  mode  (see  below)  and  is  null  otherwise.   By
       prepending ${.sh.editmode} to a value assigned to .sh.edchar it will cause the shell to change to control
       mode if it is not already in this mode.

       This trap is not invoked for characters entered as arguments to  editing  directives,  or  while  reading
       input for a character search.

   Emacs Editing Mode.
       This mode is entered by enabling either the emacs or gmacs option.  The only difference between these two
       modes is the way they handle ^T.  To edit, the user moves the cursor to the point needing correction  and
       then  inserts  or deletes characters or words as needed.  All the editing commands are control characters
       or escape sequences.  The notation for control characters is caret (^) followed by  the  character.   For
       example,  ^F  is  the  notation  for control F.  This is entered by depressing `f' while holding down the
       `CTRL' (control) key.  The `SHIFT' key is not depressed.  (The notation ^?  indicates  the  DEL  (delete)
       key.)

       The notation for escape sequences is M- followed by a character.  For example, M-f (pronounced Meta f) is
       entered by depressing ESC (ASCII 033) followed by `f'.  (M-F would be the notation for  ESC  followed  by
       `SHIFT' (capital) `F'.)

       All  edit  commands operate from any place on the line (not just at the beginning).  Neither the `RETURN'
       nor the `LINE FEED' key is entered after edit commands except when noted.

       The M-[ multi-character commands below are DEC VT220  escape  sequences  generated  by  special  keys  on
       standard  PC  keyboards,  such  as  the  arrow  keys.  You could type them directly but they are meant to
       recognize the keys in question, which are indicated in parentheses.

       ^F        Move cursor forward (right) one character.
       M-[C      (Right arrow) Same as ^F.
       M-f       Move cursor forward one word.  (The emacs editor's idea of a word is  a  string  of  characters
                 consisting of only letters, digits and underscores.)
       ^B        Move cursor backward (left) one character.
       M-[D      (Left arrow) Same as ^B.
       M-b       Move cursor backward one word.
       ^A        Move cursor to start of line.
       M-[H      (Home) Same as ^A.
       ^E        Move cursor to end of line.
       M-[F      (End) Same as ^E.
       M-[Y      Same as ^E.
       ^]char    Move cursor forward to character char on current line.
       M-^]char  Move cursor backward to character char on current line.
       ^X^X      Interchange the cursor and mark.
       erase     (User defined erase character as defined by the stty(1) command, usually ^H .)  Delete previous
                 character.
       lnext     (User defined literal next character as defined by the stty(1) command, or ^V if not  defined.)
                 Removes the next character's editing features (if any).
       ^D        Delete current character.
       M-[3~     (Forward delete) Same as ^D.
       M-d       Delete current word.
       M-^H      (Meta-backspace) Delete previous word.
       M-h       Delete previous word.
       M-^?      (Meta-DEL)  Delete  previous  word  (if your interrupt character is ^?  (DEL, the default) then
                 this command will not work).
       ^T        Transpose current character with previous character and  advance  the  cursor  in  emacs  mode.
                 Transpose two previous characters in gmacs mode.
       ^C        Capitalize current character.
       M-c       Capitalize current word.
       M-l       Change the current word to lower case.
       ^K        Delete  from  the  cursor  to  the end of the line.  If preceded by a numerical parameter whose
                 value is less than the current cursor position, then delete  from  given  position  up  to  the
                 cursor.   If  preceded  by a numerical parameter whose value is greater than the current cursor
                 position, then delete from cursor up to given cursor position.
       ^W        Kill from the cursor to the mark.
       M-p       Push the region from the cursor to the mark on the stack.
       kill      (User defined kill character as defined by the stty command, usually ^U  .)   Kill  the  entire
                 current  line.  If two kill characters are entered in succession, all kill characters from then
                 on cause a line feed (useful when using paper terminals).  A subsequent pair of kill characters
                 undoes this change.
       ^Y        Restore last item removed from line. (Yank item back to the line.)
       ^L        Line feed and print current line.
       M-^L      Clear the screen.
       ^@        (Null character) Set mark.
       M-space   (Meta space) Set mark.
       ^J        (New line) Execute the current line.
       ^M        (Return) Execute the current line.
       eof       End-of-file  character, normally ^D, is processed as an End-of-file only if the current line is
                 null.
       ^P        Fetch previous command.  Each time ^P is entered the previous command back in time is accessed.
                 Moves back one line when not on the first line of a multi-line command.
       M-[A      (Up  arrow)  If the cursor is at the end of the line, it is equivalent to ^R with string set to
                 the contents of the current line.  Otherwise, it is equivalent to ^P.
       M-<       Fetch the least recent (oldest) history line.
       M->       Fetch the most recent (youngest) history line.
       ^N        Fetch next command line.  Each time ^N is entered the next command  line  forward  in  time  is
                 accessed.
       M-[B      (Down arrow) Equivalent to ^N.
       ^Rstring  Reverse  search  history for a previous command line containing string.  If a parameter of zero
                 is given, the search is forward.  String is terminated by a `RETURN' or `NEW LINE'.  If  string
                 is  preceded  by  a ^, the matched line must begin with string.  If string is omitted, then the
                 next command line containing the most recent string is accessed.  In this case a  parameter  of
                 zero reverses the direction of the search.
       ^O        Operate  -  Execute  the current line and fetch the next line relative to current line from the
                 history file.
       M-digits  (Escape) Define numeric parameter, the digits are taken as a parameter  to  the  next  command.
                 The  commands that accept a parameter are ^F, ^B, erase, ^C, ^D, ^K, ^R, ^P, ^N, ^], M-., M-^],
                 M-_, M-=, M-b, M-c, M-d, M-f, M-h, M-l, M-^H, and the arrow keys and forward-delete key.
       M-letter  Soft-key - Your alias list is searched for an alias by the name _letter and if an alias of this
                 name  is defined, its value will be inserted on the input queue.  The letter must not be one of
                 the above meta-functions.
       M-[letter Soft-key - Your alias list is searched for an alias by the name __letter and  if  an  alias  of
                 this  name  is  defined,  its  value  will be inserted on the input queue.  This can be used to
                 program function keys on many terminals.
       M-.       The last word of the previous command is inserted on  the  line.   If  preceded  by  a  numeric
                 parameter,  the  value  of  this parameter determines which word to insert rather than the last
                 word.
       M-_       Same as M-..
       M-*       Attempt pathname expansion on the current word.  An asterisk is appended if  the  word  doesn't
                 match any file or contain any special pattern characters.
       M-ESC     Command or file name completion as described above.
       ^I tab    Attempts  command  or file name completion as described above.  If a partial completion occurs,
                 repeating this will behave as if M-= were entered.  If no  match  is  found  or  entered  after
                 space, a tab is inserted.
       M-=       If  not  preceded  by  a  numeric parameter, it generates the list of matching commands or file
                 names as described above.  Otherwise, the word  under  the  cursor  is  replaced  by  the  item
                 corresponding to the value of the numeric parameter from the most recently generated command or
                 file list.  If the cursor is not on a word, it is inserted instead.
       ^U        Multiply parameter of next command by 4.
       \         If the backslashctrl shell option is on (which is the default setting), this escapes  the  next
                 character.   Editing  characters, the user's erase, kill and interrupt (normally ^C) characters
                 may be entered in a command line or in a search string if preceded by a \.  The \  removes  the
                 next  character's  editing features (if any).  See also lnext which is not subject to any shell
                 option.
       M-^V      Display version of the shell.
       M-#       If the line does not begin with a #, a # is inserted at the beginning of  the  line  and  after
                 each  new-line,  and  the line is entered.  This causes a comment to be inserted in the history
                 file.  If the line begins with a #, the # is deleted and one #  after  each  new-line  is  also
                 deleted.

   Vi Editing Mode.
       There are two typing modes.  Initially, when you enter a command you are in the input mode.  To edit, the
       user enters control mode by typing ESC (033) and moves the cursor to the  point  needing  correction  and
       then  inserts  or deletes characters or words as needed.  Most control commands accept an optional repeat
       count prior to the command.

       The notation for control characters used below is ^ followed by a character. For instance, ^H is  entered
       by  holding  down  the  Control  key  and  pressing H.  ^[ (Control+[) is equivalent to the ESC key.  The
       notation for escape sequences is ^[ followed by one or more characters.

       The ^[[ (ESC [) multi-character commands below are DEC VT220 escape sequences generated by  special  keys
       on standard PC keyboards, such as the arrow keys, which are indicated in parentheses. When in input mode,
       these keys will switch you to control mode before performing the associated action.  These sequences  can
       use  preceding  repeat  count  parameters, but only when the ^[ and the subsequent [ are entered into the
       input buffer at the same time, such as when pressing one of those keys.

        Input Edit Commands
              By default the editor is in input mode.
              erase     (User defined erase character as defined by the stty command, usually ^H or #.)   Delete
                        previous character.
              ^W        Delete  the  previous  blank  separated  word.   On some systems the viraw option may be
                        required for this to work.
              eof       As the first character of the line causes the shell to terminate  unless  the  ignoreeof
                        option is set.  Otherwise this character is ignored.
              lnext     (User  defined  literal  next character as defined by the stty(1) or ^V if not defined.)
                        Removes the next character's editing features (if  any).   On  some  systems  the  viraw
                        option may be required for this to work.
              \         If the backslashctrl shell option is on (which is the default setting), this escapes the
                        next erase or kill character.
              ^I tab    Attempts command or file name completion as described above and returns to  input  mode.
                        If  a  partial  completion  occurs, repeating this will behave as if = were entered from
                        control mode.  If no match is found or entered after space, a tab is inserted.
        Motion Edit Commands
              These commands will move the cursor.
              [count]l  Cursor forward (right) one character.
              [count]^[[C
                        (Right arrow) Same as l.
              [count]w  Cursor forward one alphanumeric word.
              [count]W  Cursor to the beginning of the next word that follows a blank.
              [count]e  Cursor to end of word.
              [count]E  Cursor to end of the current blank delimited word.
              [count]h  Cursor backward (left) one character.
              [count]^[[D
                        (Left arrow) Same as h.
              [count]b  Cursor backward one word.
              [count]B  Cursor to preceding blank separated word.
              [count]|  Cursor to column count.
              [count]fc Find the next character c in the current line.
              [count]Fc Find the previous character c in the current line.
              [count]tc Equivalent to f followed by h.
              [count]Tc Equivalent to F followed by l.
              [count];  Repeats count times, the last single character find command, f, F, t, or T.
              [count],  Reverses the last single character find command count times.
              0         Cursor to start of line.
              ^[[H      (Home) Same as 0.
              ^         Cursor to first non-blank character in line.
              $         Cursor to end of line.
              ^[[F      (End) Same as $.
              ^[[Y      Same as $.
              %         Moves to balancing (, ), {, }, [,  or  ].   If  cursor  is  not  on  one  of  the  above
                        characters, the remainder of the line is searched for the first occurrence of one of the
                        above characters first.
        Search Edit Commands
              These commands access your command history.
              [count]k  Fetch previous command.  Each time k is entered the previous command  back  in  time  is
                        accessed.
              [count]-  Equivalent to k.
              [count]^[[A
                        (Up  arrow) If cursor is at the end of the line it is equivalent to / with string set to
                        the contents of the current line.  Otherwise, it is equivalent to k.
              [count]j  Fetch next command.  Each time j  is  entered  the  next  command  forward  in  time  is
                        accessed.
              [count]+  Equivalent to j.
              [count]^[[B
                        (Down arrow) Equivalent to j.
              [count]G  The command number count is fetched.  The default is the least recent history command.
              /string   Search  backward  through  history  for a previous command containing string.  String is
                        terminated by a `RETURN' or `NEW LINE'.  If string is preceded by a ^, the matched  line
                        must begin with string.  If string is null, the previous string will be used.
              ?string   Same as / except that search will be in the forward direction.
              n         Search for next match of the last pattern to / or ?  commands.
              N         Search for next match of the last pattern to / or ?, but in reverse direction.
        Text Modification Edit Commands
              These commands will modify the line.
              a         Enter input mode and enter text after the current character.
              A         Append text to the end of the line.  Equivalent to $a.
              [count]cmotion
              c[count]motion
                        Delete  current character through the character that motion would move the cursor to and
                        enter input mode.  If motion is c, the entire  line  will  be  deleted  and  input  mode
                        entered.
              C         Delete  the  current character through the end of line and enter input mode.  Equivalent
                        to c$.
              S         Equivalent to cc.
              [count]s  Replace characters under the cursor in input mode.
              D         Delete the current character through the end of line.  Equivalent to d$.
              [count]dmotion
              d[count]motion
                        Delete current character through the character that motion would move to.  If motion  is
                        d , the entire line will be deleted.
              i         Enter input mode and insert text before the current character.
              I         Insert text before the beginning of the line.  Equivalent to 0i.
              [count]P  Place the previous text modification before the cursor.
              [count]p  Place the previous text modification after the cursor.
              R         Enter  input  mode and replace characters on the screen with characters you type overlay
                        fashion.
              [count]rc Replace the count character(s) starting at the  current  cursor  position  with  c,  and
                        advance the cursor.
              [count]x  Delete current character.
              [count]^[[3~
                        (Forward delete) Same as x.
              [count]X  Delete preceding character.
              [count].  Repeat the previous text modification command.
              [count]  Invert  the  case  of the count character(s) starting at the current cursor position and
                        advance the cursor.
              [count]_  Causes the count word of the previous command to be appended  and  input  mode  entered.
                        The last word is used if count is omitted.
              *         Causes  an * to be appended to the current word and pathname expansion attempted.  If no
                        match is found, it rings the bell.  Otherwise, the word  is  replaced  by  the  matching
                        pattern and input mode is entered.
              \         Command or file name completion as described above.
        Other Edit Commands
              Miscellaneous commands.
              [count]ymotion
              y[count]motion
                        Yank  current  character through character that motion would move the cursor to and puts
                        them into the delete buffer.  The text and cursor are unchanged.
              yy        Yanks the entire line.
              Y         Yanks from current position to end of line.  Equivalent to y$.
              u         Undo the last text modifying command.
              U         Undo all the text modifying commands performed on the line.
              [count]v  Returns the command hist -e ${VISUAL:-${EDITOR:-vi}} count  in  the  input  buffer.   If
                        count is omitted, then the current line is used.
              ^L        Line feed and print current line.  Has effect only in control mode.
              ^J        (New line) Execute the current line, regardless of mode.
              ^M        (Return) Execute the current line, regardless of mode.
              #         If  the first character of the command is a #, then this command deletes this # and each
                        # that follows a newline.  Otherwise, sends the line after inserting a  #  in  front  of
                        each  line  in  the  command.  Useful for causing the current line to be inserted in the
                        history as a comment and uncommenting previously commented commands in the history file.
              [count]=  If count is not specified, it generates the list of matching commands or file  names  as
                        described  above.   Otherwise,  the  word under the cursor is replaced by the count item
                        from the most recently generated command or file list.  If the cursor is not on a  word,
                        it is inserted instead.
              @letter   Your  alias  list  is  searched for an alias by the name _letter and if an alias of this
                        name is defined, its value will be inserted on the input queue for processing.
              ^V        Display version of the shell.

   Built-in Commands.
       The simple-commands listed below are built in to the shell and are executed in the same  process  as  the
       shell.   The effects of any added Input/Output redirections are local to the command, except for the exec
       and redirect commands.  Unless otherwise indicated, the  output  is  written  on  standard  output  (file
       descriptor  1)  and  the exit status, when there is no syntax error, is zero.  Except for :, true, false,
       and echo, all built-in commands accept -- to indicate end of options, and are self-documenting.

       The self-documenting commands interpret the option --man as a  request  to  display  that  command's  own
       manual  page,  --help  as  a  request to display the OPTIONS section from their manual page, and -?  as a
       request to print a brief usage message.  All these are processed as error messages, so they  are  written
       on  standard  error  (file  descriptor 2) and to pipe them into a pager such as more(1) you need to add a
       2>&1 redirection before the |. The display of boldface text depends on whether standard  error  is  on  a
       terminal,  so  is  disabled  when  using a pager. Exporting the ERROR_OPTIONS environment variable with a
       value containing emphasis will force this on; a value containing noemphasis forces it  off.   The  test/[
       command needs an additional -- argument to recognize self-documentation options, e.g. test --man --.  The
       exec and redirect commands, as they make redirections permanent, should use self-documentation options in
       a  subshell  when  redirecting, for example: (redirect --man) 2>&1.  There are advanced output options as
       well; see getopts --man for more information.

       Commands that are preceded by a † symbol below are special built-in commands and are treated specially in
       the following ways:
       1.     Variable assignment lists preceding the command remain in effect when the command completes.
       2.     I/O redirections are processed after variable assignments.
       3.     Errors cause a script that contains them to abort.
       4.     They are not valid function names.
       Commands that are preceded by a ‡ symbol below are declaration commands.  Any following words that are in
       the format of a variable assignment are expanded with the same rules  as  a  variable  assignment.   This
       means   that   tilde   expansion   is  performed  after  the  =  sign,  array  assignments  of  the  form
       varname=(assign_list) are supported, and field splitting and pathname expansion are not performed.

       † : [ arg ... ]
              The command only expands parameters.

       † . name [ arg ... ]
              If name is a function defined with the  function  name  reserved  word  syntax,  the  function  is
              executed in the current environment (as if it had been defined with the name() syntax).  Otherwise
              if name refers to a file, the file is read in its entirety and the commands are  executed  in  the
              current  shell  environment.   The  search  path  specified  by PATH is used to find the directory
              containing the file.  If any arguments arg are given, they become the positional parameters  while
              processing  the  .   command  and the original positional parameters are restored upon completion.
              Otherwise the positional parameters are unchanged.  The exit status is the exit status of the last
              command executed.

       [ expression ]
              The  [  command  is  the same as test, with the exception that an additional closing ] argument is
              required. See test below.

       alias [ -ptx ]  [ name[ =value  ] ] ...
              alias with no arguments prints the list of aliases in the form name=value on standard output.  The
              -p  option  causes  the word alias to be inserted before each one.  When one or more arguments are
              given, an alias is defined for each name whose value is given.  A trailing space in  value  causes
              the next word to be checked for alias substitution.  With the -t option, each name is looked up as
              a command in $PATH and its path is added to the hash table as a 'tracked alias'.  If  no  name  is
              given, this prints the hash table. See hash.  Without the -t option, for each name in the argument
              list for which no value is given, the name and value of the alias is  printed.   The  obsolete  -x
              option  has no effect.  The exit status is non-zero if a name is given, but no value, and no alias
              has been defined for the name.

       autoload name ...
              Marks each name undefined so that the FPATH  variable  will  be  searched  to  find  the  function
              definition when the function is referenced.  The same as typeset -fu.

       bg [ job... ]
              This  command  is  only  on  systems  that  support job control.  Puts each specified job into the
              background.  The current job is put in the background if job is not specified.   See  Jobs  for  a
              description of the format of job.

       † break [ n ]
              Exit  from the enclosing for, while, until, or select loop, if any.  If n is specified, then break
              n levels.

       builtin [ -ds ] [ -f file ] [ name ... ]
              If name is not specified, and no -f option is specified, the built-ins  are  printed  on  standard
              output.   The  -s  option  prints only the special built-ins.  Otherwise, each name represents the
              pathname whose basename is the name of the built-in.  The entry point function name is  determined
              by  prepending  b_ to the built-in name.  A built-in specified by a pathname will only be executed
              when that pathname would be found during the path search.  Built-ins found in libraries loaded via
              the .paths file will associate with the pathname of the directory containing the .paths file.

              The  ISO  C/C++  prototype  is  b_mycommand(int argc, char *argv[], void *context) for the builtin
              command mycommand where argv is array an of argc elements and context is an optional pointer to  a
              Shell_t structure as described in <ast/shell.h>.

              Special  built-ins  cannot  be  bound to a pathname or deleted.  The -d option deletes each of the
              given built-ins.  On systems that support dynamic loading, the -f option names  a  shared  library
              containing  the  code for built-ins.  The shared library prefix and/or suffix, which depend on the
              system, can be omitted.  Once a library is loaded, its symbols  become  available  for  subsequent
              invocations  of  builtin.   Multiple  libraries  can be specified with separate invocations of the
              builtin command.  Libraries are searched in the reverse order in which they are specified.  When a
              library  is  loaded,  it  looks for a function in the library whose name is lib_init() and invokes
              this function with an argument of 0.

       cd [ -L ] [ -eP ] [ arg ]
       cd [ -L ] [ -eP ] old new
              This command can be in either of two forms.  In the first form it changes the current directory to
              arg.   If arg is - the directory is changed to the previous directory.  The shell variable HOME is
              the default arg.  The variable PWD is set to the current directory.   The  shell  variable  CDPATH
              defines  the  search  path  for  the  directory  containing  arg.  Alternative directory names are
              separated by a colon (:).  The default path is <null> (specifying the  current  directory).   Note
              that  the  current  directory is specified by a null path name, which can appear immediately after
              the equal sign or between the colon delimiters anywhere else in the path list.  If arg begins with
              a / then the search path is not used.  Otherwise, each directory in the path is searched for arg.
              The second form of cd substitutes the string new for the string old in the current directory name,
              PWD, and tries to change to this new directory.
              By default, symbolic link names are treated literally when finding the directory  name.   This  is
              equivalent  to the -L option.  The -P option causes symbolic links to be resolved when determining
              the directory.  The last instance of -L or -P on the command line determines which method is used.
              If -e and -P are both in effect and the correct PWD could not  be  determined  after  successfully
              changing  the  directory, cd will return with exit status one and produce no output.  If any other
              error occurs while both flags are active, the exit status is greater than one.
              The cd command may not be executed by rksh.

       command [ -pvxV ] name [ arg ... ]
              With the -v option, command is equivalent to the built-in whence command described below.  The  -V
              option causes command to act like whence -v.

              Without  the  -v  or -V options, command executes name with the arguments given by arg.  Functions
              and aliases will not be searched for when finding name.  If name refers to a special built-in,  as
              marked  with    in  this manual, command disables the special properties described above for that
              mark, executing the command as a regular built-in.  (For example, using command set -o option-name
              prevents a script from terminating when an invalid option name is given.)

              The -p option causes the operating system's standard utilities path (as output by getconf PATH) to
              be searched rather than the one defined by the value of PATH.

              The -x option runs name as an external command, bypassing built-ins.  If the arguments contain  at
              least  one word that expands to multiple arguments, such as "$@" or *.txt, then the -x option also
              allows executing external commands with argument lists that are longer than the  operating  system
              allows.  This  functionality  is  similar to xargs(1) but is easier to use. The shell does this by
              invoking the external command multiple times if needed, dividing the expanded argument  list  over
              the invocations. Any arguments that come before the first word that expands to multiple arguments,
              as well as any that follow the last such word, are considered static arguments  and  are  repeated
              for  each  invocation. This allows each invocation to use the same command options, as well as the
              same trailing destination arguments for commands like cp(1) or mv(1).  When  all  invocations  are
              completed,  command  -x  exits with the status of the invocation that had the highest exit status.
              (Note that command -x may still fail with an "argument list too long" error if a  single  argument
              exceeds the maximum length of the argument list, or if a long arguments list contains no word that
              expands to multiple arguments.)

       ‡ compound vname[=value] ...
              Causes each vname to be a compound variable.  The same as typeset -C.

       † continue [ n ]
              Resume the next iteration of the enclosing for, while, until, or select loop.  If n is  specified,
              then resume at the n-th enclosing loop.

       disown [ job... ]
              Causes the shell not to send a HUP signal to each given job, or all active jobs if job is omitted,
              when a login shell terminates.

       echo [ arg ... ]
              When the first arg does not begin with a -, and none of the  arguments  contain  a  \,  then  echo
              prints  each  of  its arguments separated by a space and terminated by a new-line.  Otherwise, the
              behavior of echo is system dependent and print or printf described  below  should  be  used.   See
              echo(1) for usage and description.

       ‡ enum [ -i  ] type[=(value ...) ]
              Creates  a  declaration  command named type that allows one of the specified values as enumeration
              names.  If =(value ...) is omitted, then type must be an indexed array variable with at least  two
              elements  and  the  values  are taken from this array variable.  If -i is specified the values are
              case-insensitive.  Declaration commands are created as special builtins that cannot be removed  or
              overridden  by  shell  functions.   Each created declaration command has a --man option that shows
              documentation on its type's behavior and possible values.

              Within arithmetic expressions (see Arithmetic Evaluation above), enumeration type values translate
              to  index  numbers  between  0  and  the  number  of defined values minus 1. It is an error for an
              arithmetic expression to assign a value outside of that range. Decimal fractions are ignored.

       † eval [ arg ... ]
              The arguments are read as input to the shell and the resulting command(s) executed.

       † exec [ -c ] [ -a name ] [ arg ... ]
              If arg is given, the command specified by the arguments is executed in place of this shell without
              creating  a  new process.  The value of the SHLVL environment variable is decreased by one, unless
              the shell replaced is a subshell.  The -c option causes  the  environment  to  be  cleared  before
              applying  variable  assignments  associated  with  the exec invocation.  The -a option causes name
              rather than the first arg, to become argv[0] for the new process.  If arg is not  given  and  only
              I/O  redirections  are  given,  then  this  command  persistently  modifies file descriptors as in
              redirect.exit [ n ]
              Causes the shell to exit with the exit status specified  by  n.   The  value  will  be  the  least
              significant  8  bits  of  n (if specified) or of the exit status of the last command executed.  An
              end-of-file will also cause the shell to exit, except  for  an  interactive  shell  that  has  the
              ignoreeof option turned on (see set below).

       †‡ export [ -p ] [ name[=value] ] ...
              If  name is not given, the names and values of each variable with the export attribute are printed
              with the values quoted in a manner that allows them to be re-input.  The  export  command  is  the
              same  as typeset -x except that if you use export within a function, no local variable is created.
              The -p option causes the word export to be inserted before each one.  Otherwise, the  given  names
              are marked for automatic export to the environment of subsequently-executed commands.

       false  Does nothing, and exits 1. Used with until for infinite loops.

       fc [ -e ename  ] [ -N num ] [ -nlr ] [ first [ last ] ]
       fc -s  [ old=new ] [ command ]
              The same as hist.

       fg [ job... ]
              This  command  is  only on systems that support job control.  Each job specified is brought to the
              foreground and waited for in the specified order.  Otherwise, the current job is brought into  the
              foreground.  See Jobs for a description of the format of job.

       ‡ float vname[=value] ...
              Declares each vname to be a long floating point number.  The same as typeset -lE.

       functions [ -Stux ] [ name ... ]
              Lists functions.  The same as typeset -f.

       getconf [ name [ pathname ] ]
              Prints  the  current  value  of  the  configuration  parameter  given  by name.  The configuration
              parameters are defined by the IEEE POSIX 1003.1 and IEEE POSIX 1003.2 standards.  (See pathconf(2)
              and  sysconf(3).)   The  pathname  argument  is required for parameters whose value depends on the
              location in the file system.  If no arguments are given, getconf prints the names  and  values  of
              the  current  configuration  parameters.   The  pathname / is used for each of the parameters that
              requires pathname.

       getopts [ -a name ] optstring vname [ arg ... ]
              Checks arg for legal options.  If arg is omitted, the positional parameters are used.   An  option
              argument  begins with a + or a -.  An option not beginning with + or - or the argument -- ends the
              options.  Options beginning with + are only recognized when optstring begins with a +.   optstring
              contains  the  letters  that  getopts  recognizes.  If a letter is followed by a :, that option is
              expected to have an argument.  The options can be separated from  the  argument  by  blanks.   The
              option  -?   causes getopts to generate a usage message on standard error.  The -a argument can be
              used to specify the name to use for the usage message, which defaults to $0.
              getopts places the next option letter it finds inside variable vname each time it is invoked.  The
              option  letter  will be prepended with a + when arg begins with a +.  The index of the next arg is
              stored in OPTIND.  The option argument, if any, gets stored in OPTARG.
              A leading : in optstring causes getopts to store the letter of an invalid option in OPTARG, and to
              set  vname  to  ?   for  an  unknown  option  and to : when a required option argument is missing.
              Otherwise, getopts prints an error message.  The exit status is non-zero when there  are  no  more
              options.
              There  is  no  way  to  specify any of the options :, +, -, ?, [, and ].  The option # can only be
              specified as the first option.

       hash [ -r ] [ utility ]
              hash displays or modifies the hash table with the locations of recently used programs. If given no
              arguments,  it  lists  all command/path associations (a.k.a. 'tracked aliases') in the hash table.
              Otherwise, hash performs a PATH search for each utility supplied and adds the result to  the  hash
              table.  The -r option empties the hash table. This can also be achieved by resetting PATH.

       hist [ -e ename  ] [ -N num ] [ -nlr ] [ first [ last ] ]
       hist -s [ old=new ] [ command ]
              In  the  first  form,  a  range  of commands from first to last is selected from the last HISTSIZE
              commands that were typed at the terminal.  The arguments first and last  may  be  specified  as  a
              number or as a string.  A string is used to locate the most recent command starting with the given
              string.  A negative number is used as an offset to the current command number.  If the  -l  option
              is  selected,  the commands are listed on standard output.  Otherwise, the editor program ename is
              invoked on a file containing these keyboard commands.  If ename is not supplied, then the value of
              the  variable  HISTEDIT is used.  If HISTEDIT is not set, then FCEDIT (default /bin/ed) is used as
              the editor.  When editing is complete, the edited command(s) is executed if the changes have  been
              saved.   If  last  is not specified, then it will be set to first.  If first is not specified, the
              default is the previous command for editing and -16 for listing.  The option -r reverses the order
              of  the  commands  and the option -n suppresses command numbers when listing.  In the second form,
              command is interpreted as first described above and defaults to the last  command  executed.   The
              resulting command is executed after the optional substitution old=new is performed.  The option -N
              causes hist to start num commands back.

       ‡ integer vname[=value] ...
              Declares each vname to be a long integer number.  The same as typeset -li.

       jobs [ -lnp ] [ job ... ]
              Lists information about each given job; or all active jobs if job is omitted.  The -l option lists
              process  ids  in  addition  to the normal information.  The -n option only displays jobs that have
              stopped or exited since last notified.  The -p option causes only the process group to be  listed.
              See Jobs for a description of the format of job.

       kill [ -s signame ] job ...
       kill [ -n signum ] job ...
       kill -Ll [ sig ... ]
              Sends  either  the  TERM  (terminate)  signal  or  the  specified  signal to the specified jobs or
              processes.  Signals are either given by number with the -n option or by name with  the  -s  option
              (as  given  in  <signal.h>, stripped of the prefix ``SIG'' with the exception that SIGCLD is named
              CHLD).  For backward compatibility, the n and s can be omitted  and  the  number  or  name  placed
              immediately  after  the -.  If the signal being sent is TERM (terminate) or HUP (hangup), then the
              job or process will be sent a CONT (continue) signal if it is stopped.  The argument  job  can  be
              the  process  id  of  a  process  that  is not a member of one of the active jobs.  See Jobs for a
              description of the format of job.  In the third  form,  kill  -l,  or  kill  -L,  if  sig  is  not
              specified,  the  signal  names  are listed.  The -l option list only the signal names.  -L options
              lists each signal name and corresponding number.  Otherwise, for each sig  that  is  a  name,  the
              corresponding  signal  number  is  listed.   For  each  sig  that  is  a  number,  the signal name
              corresponding to the least significant 8 bits of sig is listed.

       let arg ...
              Each arg is a separate arithmetic expression to be evaluated.  let only recognizes  octal  numbers
              starting  with  0  when  the  set  option  letoctal  is on.  See Arithmetic Evaluation above for a
              description of arithmetic expression evaluation.
              The exit status is 0 if the value of the last expression is non-zero, and 1 otherwise.

       ‡ nameref vname[=refname] ...
              Declares each vname to be a variable name reference.  The same as typeset -n.

       print [ -CRenprsv ] [ -u unit ] [ -f format ] [ arg ... ]
              With no options or with option - or --, each arg is printed on standard  output.   The  -f  option
              causes  the  arguments to be printed as described by printf.  In this case, any e, n, r, R options
              are ignored.  Otherwise, unless the -C,  -R,  -r,  or  -v  are  specified,  the  following  escape
              conventions will be applied:
              \a     The alert character (ASCII 07).
              \b     The backspace character (ASCII 010).
              \c     Causes print to end without processing more arguments and not adding a new-line.
              \f     The formfeed character (ASCII 014).
              \n     The newline character (ASCII 012).
              \r     The carriage return character (ASCII 015).
              \t     The tab character (ASCII 011).
              \v     The vertical tab character (ASCII 013).
              \E     The escape character (ASCII 033).
              \\     The backslash character \.
              \0x    The character defined by the 1, 2, or 3-digit octal string given by x.

              The  -R  option  will print all subsequent arguments and options other than -n.  The -e causes the
              above escape conventions to be applied.  This is the default behavior.  It reverses the effect  of
              an  earlier  -r.   The  -p  option causes the arguments to be written onto the pipe of the process
              spawned with |& instead of standard output.  The -v option treats each arg as a variable name  and
              writes  the  value  in the printf %B format.  The -C option treats each arg as a variable name and
              writes the value in the printf %#B format.  The -s option causes the arguments to be written  onto
              the  history  file  instead  of standard output.  The -u option can be used to specify a one digit
              file descriptor unit number unit on which the output will be placed.  The default is  1.   If  the
              option -n is used, no new-line is added to the output.

       printf [ -v vname ] format [ arg ... ]
              The  arguments  arg  are printed on standard output in accordance with the ANSI C formatting rules
              associated with the format string format.  If the number of arguments exceeds the number of format
              specifications,  the  format  string  is  reused  to  format  remaining  arguments.  The following
              extensions can also be used:
              %b     A %b format can be used instead of %s to cause escape sequences in the corresponding arg to
                     be expanded as described in print.
              %B     A  %B  option  causes  each of the arguments to be treated as variable names and the binary
                     value of variable will be printed.  The alternate flag # causes a compound variable  to  be
                     output  on  a  single line.  This is most useful for compound variables and variables whose
                     attribute is -b.
              %H     A %H format can be used instead of %s to cause characters in arg that are special  in  HTML
                     and XML to be output as their entity name.  The alternate flag # formats the output for use
                     as a URI.
              %p     A %p format will convert the given number to hexadecimal.
              %P     A %P format can be used instead of %s to cause arg to be interpreted as an extended regular
                     expression and be printed as a shell pattern.
              %q     A  %q  format  can  be  used  instead of %s to cause the resulting string to be quoted in a
                     manner than can be reinput to the shell.  When q is  preceded  by  the  alternative  format
                     specifier, #, the string is quoted in manner suitable as a field in a .csv format file.
              %(date-format)T
                     A  %(date-format)T  format  can  be  used to treat an argument as a date/time string and to
                     format the date/time according to the date-format.
              %Q     A %Q format will convert the given number of seconds to readable time.
              %R     A %R format can be used instead of %s to cause arg to be interpreted as a shell pattern and
                     to be printed as an extended regular expression.
              %Z     A %Z format will output a byte whose value is 0.
              %d     The  precision field of the %d format can be followed by a .  and the output base.  In this
                     case, the # flag character causes base# to be prepended.
              #      The # flag, when used with the %d format without an output base,  displays  the  output  in
                     powers  of 1000 indicated by one of the following suffixes: k M G T P E, and when used with
                     the %i format displays the output in powers of 1024  indicated  by  one  of  the  following
                     suffixes: Ki Mi Gi Ti Pi Ei.
              =      The = flag centers the output within the specified field width.
              L      The  L  flag,  when  used  with  the  %c or %s formats, treats precision as character width
                     instead of byte count.
              ,      The , flag, when used with the %d or %f  formats,  separates  groups  of  digits  with  the
                     grouping delimiter (, on groups of 3 in the C locale).

              The -v option assigns the output directly to a variable instead of
                     writing  it  to  standard  output. This is faster than capturing the output using a command
                     substitution and avoids the latter's stripping of final linefeed characters (\n). The vname
                     argument  should  be a valid variable name, optionally with one or more array subscripts in
                     square brackets.  Note that square brackets should be quoted to avoid pathname expansion.

       pwd [ -LP ]
              Outputs the value of the current working directory.  The -L option is the default; it  prints  the
              logical name of the current directory.  If the -P option is given, all symbolic links are resolved
              from the name.  The last instance of -L or -P on the command line determines which method is used.

       read [ -ACSprsv ] [ -d delim ] [ -n n ] [ [ -N n ] [ -t timeout ] [ -u unit ] [ vname?prompt  ]  [  vname
       ... ]
              The  shell input mechanism.  One line is read and is broken up into fields using the characters in
              IFS as separators.  The escape character, \, is used to remove any special meaning  for  the  next
              character  and  for  line  continuation.   The  -d option causes the read to continue to the first
              character of delim rather than new-line.  The -n option causes at most n bytes to  read  rather  a
              full  line  but  will  return  when reading from a slow device as soon as any characters have been
              read.  The -N option causes exactly n to be read unless an end-of-file has been encountered or the
              read  times  out  because  of  the  -t  option.   In  raw mode, -r, the \ character is not treated
              specially.  The first field is assigned to the first vname, the second field to the second  vname,
              etc., with leftover fields assigned to the last vname.  When vname has the binary attribute and -n
              or -N is specified, the bytes that are read are stored directly into the variable.  If the  -v  is
              specified,  then  the value of the first vname will be used as a default value when reading from a
              terminal device.  The -A option causes the variable vname to be unset and each field that is  read
              to be stored in successive elements of the indexed array vname.  The -C option causes the variable
              vname to be read as a compound variable.  Blanks will be ignored when finding the  beginning  open
              parenthesis.   The  -S option causes the line to be treated like a record in a .csv format file so
              that double quotes can be used to allow the delimiter character  and  the  new-line  character  to
              appear  within  a field.  The -p option causes the input line to be taken from the input pipe of a
              process spawned by the shell using |&.  If the -s option is present, the input will be saved as  a
              command  in  the  history  file.  The option -u can be used to specify a one digit file descriptor
              unit unit to read from.  The file descriptor can be opened with the exec special built-in command.
              The  default  value  of  unit  n is 0.  The option -t is used to specify a timeout in seconds when
              reading from a terminal or pipe.  If vname is omitted, then REPLY is used as  the  default  vname.
              An  end-of-file with the -p option causes cleanup for this process so that another can be spawned.
              If the first argument contains a ?, the remainder of this word is used as  a  prompt  on  standard
              error when the shell is interactive.  The exit status is 0 unless an end-of-file is encountered or
              read has timed out.

       †‡ readonly [ -p ] [ vname[=value] ] ...
              If vname is not given, the names and values of each  variable  with  the  read-only  attribute  is
              printed  with the values quoted in a manner that allows them to be re-input.  The -p option causes
              the word readonly to be inserted before each one.  Otherwise, the given vnames  are  marked  read-
              only  and  these  names  cannot be changed by subsequent assignment.  Unlike typeset -r , readonly
              does not create a function-local scope and the given  vnames  are  marked  globally  read-only  by
              default.   When defining a type, if the value of a read-only subvariable is not defined, the value
              is required when creating each instance.

       redirect
              This command only accepts input/output redirections.  It can open and close files and modify  file
              descriptors  from  0  to 9 as specified by the input/output redirection list (see the Input/Output
              section above), with the difference that the effect persists past the execution  of  the  redirect
              command.   When  invoking  another  program, file descriptors greater than 2 that were opened with
              this mechanism are only passed on if they are explicitly redirected to themselves as part  of  the
              invocation (e.g. 4>&4) or if the posix option is set.

       † return [ n ]
              Causes  a  shell  function,  dot  script  (see  .  and source), or profile script to return to the
              invoking shell environment with the exit status specified by n.  This status  value  can  use  the
              full  signed  integer  range as shown by the commands getconf INT_MIN and getconf INT_MAX. A value
              outside that range will produce a warning and an exit status of 128.  If n is  omitted,  then  the
              value  of  $?  is  assumed,  i.e.,  the exit status of the last command executed is passed on.  If
              return is invoked while not in a function, dot script, or profile script, then it behaves the same
              as exit.

       † set [ ±BCGHabefhkmnprstuvx ] [ ±o [ option ] ] ... [ ±A vname ]  [ arg ... ]
              The options for this command have meaning as follows:
              -A      Array  assignment.   Unset  the variable vname and assign values sequentially from the arg
                      list.  If +A is used, the variable vname is not unset first.
              -B      Enable brace group expansion. On by default, except if ksh is invoked as sh or rsh.
              -C      Prevents redirection > from truncating existing files.  Files that are created are  opened
                      with the O_EXCL mode.  Requires >| to truncate a file when turned on.
              -G      Enables  recursive  pathname  expansion.   This  adds  the  double-star  pattern ** to the
                      pathname expansion (see Pathname Expansion above).  By itself, it  matches  the  recursive
                      contents  of  the  current  directory,  which  is to say, all files and directories in the
                      current directory and in all its subdirectories, sub-subdirectories, and so  on.   If  the
                      pathname  pattern  ends in **/, only directories and subdirectories are matched, including
                      symbolic links that point to directories.  A prefixed directory name is  not  included  in
                      the  results  unless  that  directory  was  itself found by a pattern. For example, dir/**
                      matches the recursive contents of dir but not dir itself, whereas  di[r]/**  matches  both
                      dir  itself  and the recursive contents of dir.  Symbolic links to non-directories are not
                      followed.  Symbolic links to directories are followed if they are specified  literally  or
                      match  a  pattern  as  described  under  Pathname Expansion, but not if they result from a
                      double-star pattern.
              -H      Enable !-style history expansion similar to csh(1).
              -a      All subsequent variables that are defined are automatically exported.
              -b      Prints job completion messages as soon as a  background  job  changes  state  rather  than
                      waiting for the next prompt.
              -e      Unless  contained  in  a  ||  or && command, or the command following an if while or until
                      command or in the pipeline following !, if a command has a non-zero exit  status,  execute
                      the ERR trap, if set, and exit.  This mode is disabled while reading profiles.
              -f      Disables pathname expansion.
              -h      Each command becomes a tracked alias when first encountered.
              -k      (Obsolete). All variable assignment arguments are placed in the environment for a command,
                      not just those that precede the command name.
              -m      Background jobs will run  in  a  separate  process  group  and  a  line  will  print  upon
                      completion.   The  exit status of background jobs is reported in a completion message.  On
                      systems with job control, this option is turned on automatically for interactive shells.
              -n      Read commands and check them for syntax errors, but do  not  execute  them.   Ignored  for
                      interactive shells.
              -o      The following argument can be one of the following option names:
                      allexport
                              Same as -a.
                      backslashctrl
                              The backslash character \ escapes the next control character in the emacs built-in
                              editor and the next erase or kill character in the  vi  built-in  editor.   On  by
                              default.
                      bgnice  All background jobs are run at a lower priority.  This is the default mode.
                      braceexpand
                              Same as -B.
                      emacs   Puts you in an emacs style in-line editor for command entry.
                      errexit Same as -e.
                      globcasedetect
                              When  this  option  is turned on, globbing (see Pathname Expansion above) and file
                              name listing and completion (see  In-line  Editing  Options  above)  automatically
                              become  case-insensitive  on  file systems where the difference between upper- and
                              lowercase is ignored for file names. This is  transparently  determined  for  each
                              directory,  so  a  path pattern that spans multiple file systems can be part case-
                              sensitive and part case-insensitive.  In more precise terms, each  slash-separated
                              path  name component pattern p is treated as ~(i:p) if its parent directory exists
                              on a case-insensitive file system.  This  option  is  only  present  on  operating
                              systems that support case-insensitive file systems.
                      globstar
                              Same as -G.
                      gmacs   Puts you in a gmacs style in-line editor for command entry.
                      histexpand
                              Same as -H.
                      ignoreeof
                              An interactive shell will not exit on end-of-file.  The command exit must be used.
                      keyword Same as -k.
                      letoctal
                              The  let  command  allows  octal numbers starting with 0.  On by default if ksh is
                              invoked as sh or rsh.
                      markdirs
                              All directory names resulting from pathname expansion have a trailing / appended.
                      monitor Same as -m.
                      multiline
                              The built-in editors will use multiple lines on the  screen  for  lines  that  are
                              longer than the width of the screen.  This may not work for all terminals.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Obsolete; has no effect.
                      notify  Same as -b.
                      nounset Same as -u.
                      pipefail
                              A  pipeline will not complete until all components of the pipeline have completed,
                              and the return value will be the value of the last non-zero  command  to  fail  or
                              zero if no command has failed.
                      posix   Enables  the  POSIX  standard  mode for maximum compatibility with other compliant
                              shells. At the moment that the posix  option  is  turned  on,  it  also  turns  on
                              letoctal  and  turns  off -B/braceexpand; the reverse is done when posix is turned
                              back off. (These options  can  still  be  controlled  independently  in  between.)
                              Furthermore, the posix option is automatically turned on upon invocation if ksh is
                              invoked as sh or rsh. In that case, or if the option is turned on by specifying -o
                              posix  on  the  invocation command line, the invoked shell will not set the preset
                              aliases even if interactive, and will not import  type  attributes  for  variables
                              (such as integer or left/right justify) from the environment.
                              In addition, while on, the posix option
                              •  disables  exporting  variable  type attributes to the environment for other ksh
                                 processes to import;
                              •  causes file descriptors > 2 to be left open when invoking another program;
                              •  disables the &> redirection shorthand;
                              •  makes the <> redirection operator default to redirecting standard input  if  no
                                 file descriptor number precedes it;
                              •  disables  the  special  floating  point  constants  Inf  and  NaN in arithmetic
                                 evaluation so that, e.g., $((inf)) and $((nan)) refer to the variables by those
                                 names;
                              •  enables the recognition of a leading zero as introducing an octal number in all
                                 arithmetic evaluation contexts, except in the let built-in  while  letoctal  is
                                 off;
                              •  stops the . command (but not source) from looking up functions defined with the
                                 function syntax;
                              •  changes the test/[ built-in command to make its deprecated expr1 -a  expr2  and
                                 expr1  -o expr2 operators work even if expr1 equals "!" or "(" (which means the
                                 nonstandard unary -a file and -o option operators cannot  be  directly  negated
                                 using ! or wrapped in parentheses); and
                              •  disables a hack that makes test -t ([ -t ]) equivalent to test -t 1 ([ -t 1 ]).
                      privileged
                              Same as -p.
                      showme  When  enabled,  simple  commands  or pipelines preceded by a semicolon (;) will be
                              displayed as if  the  xtrace  option  were  enabled  but  will  not  be  executed.
                              Otherwise, the leading ; will be ignored.
                      trackall
                              Same as -h.
                      verbose Same as -v.
                      vi      Puts  you  in  insert  mode  of a vi style in-line editor until you hit the escape
                              character 033.  This puts you in control mode.  A return sends the line.
                      viraw   Each character is processed as it is typed in vi mode.  The shell  may  have  been
                              compiled  to  force  this option on at all times.  Otherwise, canonical processing
                              (line-by-line input) is initially enabled and the  command  line  will  be  echoed
                              again  if the speed is 1200 baud or greater and it contains any control characters
                              or less than one second  has  elapsed  since  the  prompt  was  printed.  The  ESC
                              character terminates canonical processing for the remainder of the command and the
                              user can then modify the command line. This scheme has the advantages of canonical
                              processing  with  the  type-ahead echoing of raw mode. If the viraw option is set,
                              the terminal will  always  have  canonical  processing  disabled.   This  mode  is
                              implicit for systems that do not support two alternate end of line delimiters, and
                              may be helpful for certain terminals.
                      xtrace  Same as -x.
                      If no option name is supplied, then the current option settings are printed.
              -p      Disables processing of the $HOME/.profile file and uses the file /etc/suid_profile instead
                      of  the  ENV  file.   This mode is on whenever the effective uid (gid) is not equal to the
                      real uid (gid).  Turning this off causes the effective uid and gid to be set to  the  real
                      uid and gid.
              -r      Enables the restricted shell.  This option cannot be unset once set.
              -s      Sort the positional parameters lexicographically.
              -t      (Obsolete).  Exit after reading and executing one command.
              -u      Treat unset parameters as an error when substituting.  $@ and $* are exempt.
              -v      Print shell input lines as they are read.
              -x      Print commands and their arguments as they are executed.
              --      Do not change any of the options; useful in setting $1 to a value beginning with -.  If no
                      arguments follow this option then the positional parameters are unset.

              As an obsolete feature, if the first arg is - then the -x and -v options are turned  off  and  the
              next  arg  is  treated  as  the  first argument.  Using + rather than - causes these options to be
              turned off.  These options can also be used upon invocation of the  shell.   The  current  set  of
              options  may  be  found  in  $-.   Unless  -A is specified, the remaining arguments are positional
              parameters and are assigned, in order, to $1 $2 ....  If no arguments are given,  then  the  names
              and values of all variables are printed on the standard output.

       † shift [ n ]
              The positional parameters from $n+1 ...  are renamed $1 ... , default n is 1.  The parameter n can
              be any arithmetic expression that evaluates to a non-negative number less than or equal to $#.

       sleep [ -s ] duration
              Suspends execution for the number of decimal seconds or fractions of a second given  by  duration.
              duration  can  be  an  integer, floating point value or ISO 8601 duration specifying the length of
              time to sleep.  The option -s causes the sleep builtin to terminate when it receives  any  signal.
              If duration is not specified in conjunction with -s, sleep will wait for a signal indefinitely.

       source name [ arg ... ]
              Same as ., except it is not treated as a special built-in command.

       stop job ...
              Sends  a  SIGSTOP  signal  to  one  or more processes specified by job, suspending them until they
              receive SIGCONT.  The same as kill -s STOP.

       suspend
              Sends a SIGSTOP signal to the main shell process, suspending the script  or  child  shell  session
              until  it  receives  SIGCONT  (for  instance,  when  typing fg in the parent shell). Equivalent to
              kill -s STOP "$$", except that it accepts no operands and refuses to suspend a login shell.

       test expression
              The test and [ commands execute conditional expressions similar to  those  specified  for  the  [[
              compound  command under Conditional Expressions above, but with several important differences. The
              =, == and != operators test for string (in)equality without pattern matching;  ==  is  nonstandard
              and  unportable.  The  f3&&  and  ||  operators  are  not available. Instead, the -a and -o binary
              operators can be used, but they are fraught with  pitfalls  due  to  grammatical  ambiguities  and
              therefore  deprecated in favor of invoking separate test commands. Most importantly, as test and [
              are simple regular commands, field splitting and pathname expansion are  performed  on  all  their
              arguments  and  all  aspects of regular shell grammar (such as redirection) remain active. This is
              usually harmful, so care must be taken to quote arguments and expansions to avoid this.  To  avoid
              the  many  pitfalls arising from these issues, the [[ compound command should be used instead. The
              primary purpose of the test and [ commands is compatibility with other shells that lack [[.

              The test/[ command does not parse options except if there are two arguments and the second is  --.
              To  access  the  inline  documentation  with  an  option  such as --man, you need one of the forms
              test --man -- or [ --man -- ].

       times  Displays the accumulated user and system CPU times, one line with the times used by the shell  and
              another with those used by all of the shell's child processes. No options are supported.

       † trap [ -p ] [ action ] [ sig ] ...
              The -p option causes the trap action associated with each trap as specified by the arguments to be
              printed with appropriate quoting.  Otherwise, action will be processed as if it were  an  argument
              to  eval  when the shell receives signal(s) sig.  Each sig can be given as a number or as the name
              of the signal.  Trap commands are executed in order of signal number.  Any attempt to set  a  trap
              on  a  signal that was ignored on entry to the current shell is ineffective.  If action is omitted
              and the first sig is a number, or if action is -, then the trap(s) for each sig are reset to their
              original values.  If action is the null string then this signal is ignored by the shell and by the
              commands it invokes.  If sig is ERR then action will be executed whenever a command has a non-zero
              exit  status.   If  sig  is  DEBUG then action will be executed before each command.  The variable
              .sh.command will contain the current command line when action is running, in the  same  format  as
              the output generated by the xtrace option (minus the preceding PS4 prompt).  If the exit status of
              the trap is 2 the command will not be executed.  If the exit status of the trap is 255 and  inside
              a  function  or a dot script, the function or dot script will return.  If sig is 0 or EXIT and the
              trap statement is executed inside the body of a function defined with the  function  name  syntax,
              then  the command action is executed after the function completes.  If sig is 0 or EXIT for a trap
              set outside any function then the command action is executed on exit from the shell.   If  sig  is
              KEYBD, then action will be executed whenever a key is read while in emacs, gmacs, or vi mode.  The
              trap command with no arguments prints a list of commands associated with each signal number.

       An exit or return without an argument in a trap action will preserve the exit status of the command  that
       invoked the trap.

       true   Does nothing, and exits 0. Used with while for infinite loops.

       type [ -afpq ] name ...
              The same as whence -v.

       †‡  typeset [ ±ACHSbflmnprstux ] [ ±EFLRXZi[n] ]   [ +-M  [ mapname ] ] [ -T  [ tname=(assign_list) ] ] [
       -h str ] [ -a [type] ] [ vname[=value ]  ] ...
              Sets attributes and values for shell variables and functions.   When  invoked  inside  a  function
              defined  with  the  function name syntax, a new instance of the variable vname is created, and the
              variable's value and type are restored  when  the  function  completes.   The  following  list  of
              attributes may be specified:
              -A     Declares  vname  to be an associative array.  Subscripts are strings rather than arithmetic
                     expressions.
              -C     Causes each vname to be a compound variable. If value names  a  compound  variable,  it  is
                     copied into vname.  Otherwise, the empty compound value is assigned to vname.
              -a     Declares  vname  to  be  an indexed array.  If type is specified, it must be the name of an
                     enumeration type created with the enum command and it allows enumeration  constants  to  be
                     used as subscripts.
              -E     Declares  vname  to  be  a  double  precision  floating point number.  If n is non-zero, it
                     defines the number of significant figures that are used when expanding  vname.   Otherwise,
                     ten significant figures will be used.
              -F     Declares  vname  to  be  a  double  precision  floating point number.  If n is non-zero, it
                     defines the number of places after the decimal point that are used  when  expanding  vname.
                     Otherwise ten places after the decimal point will be used.
              -H     This option provides UNIX to host-name file mapping on non-UNIX machines.
              -L     Left  justify and remove leading blanks from value.  If n is non-zero, it defines the width
                     of the field, otherwise it is determined by the width of the  value  of  first  assignment.
                     When  the  variable  is assigned to, it is filled on the right with blanks or truncated, if
                     necessary, to fit into the field.  The -R option is turned off.
              -M     Use the character mapping mapping defined by wctrans(3).  such as tolower and toupper  when
                     assigning  a  value to each of the specified operands.  When mapping is specified and there
                     are not operands, all variables that use this mapping are written to standard output.  When
                     mapping  is omitted and there are no operands, all mapped variables are written to standard
                     output.
              -R     Right justify and fill with leading blanks.  If n is non-zero, it defines the width of  the
                     field, otherwise it is determined by the width of the value of first assignment.  The field
                     is left filled with blanks or truncated from the end if the variable is reassigned.  The -L
                     option is turned off.
              -S     When  used within the assign_list of a type definition, it causes the specified subvariable
                     to be shared by all instances of the type.  When used inside a function  defined  with  the
                     function   reserved  word,  the  specified  variables  will  have  function  static  scope.
                     Otherwise, the variable is unset prior to processing the assignment list.
              -T     If followed by tname, it creates a type  named  by  tname  using  the  compound  assignment
                     assign_list to tname.  Otherwise, it writes all the type definitions to standard output.
              -X     Declares  vname  to  be  a  double precision floating point number and expands using the %a
                     format of ISO-C99.  If n is non-zero, it defines the number of hex digits after  the  radix
                     point that is used when expanding vname.  The default is 10.
              -Z     Right  justify  and fill with leading zeros if the first non-blank character is a digit and
                     the -L option has not been set.  Remove leading zeros if the -L option is also set.   If  n
                     is  non-zero, it defines the width of the field, otherwise it is determined by the width of
                     the value of first assignment.
              -f     The names refer to function names rather than variable names.  No assignments can  be  made
                     and the only other valid options are -S, -t, -u and -x.  The -S can be used with discipline
                     functions defined in a type to  indicate  that  the  function  is  static.   For  a  static
                     function,  the  same  method  will  be  used  by all instances of that type no matter which
                     instance references it.  In addition, it can only use value of variables from the  original
                     type definition.  These discipline functions cannot be redefined in any type instance.  The
                     -t option turns on execution tracing for this function.  The -u option causes this function
                     to  be  marked  undefined.   The  FPATH  variable  will  be  searched  to find the function
                     definition when the function is referenced.  If no options other than -f is specified, then
                     the  function  definition will be displayed on standard output.  If +f is specified, then a
                     line containing the function name followed by a shell comment containing  the  line  number
                     and  path name of the file where this function was defined, if any, is displayed.  The exit
                     status can be used to determine  whether  the  function  is  defined  so  that  typeset  -f
                     .sh.math.name will return 0 when math function name is defined and non-zero otherwise.
              -b     The  variable  can  hold any number of bytes of data.  The data can be text or binary.  The
                     value is represented by the base64 encoding of the data.  If -Z is also specified, the size
                     in  bytes  of the data in the buffer will be determined by the size associated with the -Z.
                     If the base64 string assigned results in more data, it will be  truncated.   Otherwise,  it
                     will  be filled with bytes whose value is zero.  The printf format %B can be used to output
                     the actual data in this buffer instead of the base64 encoding of the data.
              -h     Used within type definitions to add  information  when  generating  information  about  the
                     subvariable  on  the man page.  It is ignored when used outside of a type definition.  When
                     used with -f the information is associated with the corresponding discipline function.
              -i     Declares vname to be represented  internally  as  integer.   The  right  hand  side  of  an
                     assignment  is evaluated as an arithmetic expression when assigning to an integer.  If n is
                     non-zero, it defines the output arithmetic base, otherwise the output base will be ten.
              -l     Used with -i, -E or -F, to indicate long integer, or long float.  Otherwise, all  uppercase
                     characters  are  converted  to  lowercase.   The  uppercase  option,  -u,  is  turned  off.
                     Equivalent to -M tolower .
              -m     moves or renames the variable.  The value is the name of a variable  whose  value  will  be
                     moved  to  vname.   The  original  variable  will  be unset.  Cannot be used with any other
                     options.
              -n     Declares vname to be a reference to the variable whose name is  defined  by  the  value  of
                     variable  vname.  This is usually used to reference a variable inside a function whose name
                     has been passed as an argument.  Cannot be used with any other options.
              -p     The name, attributes and values for the given vnames are written on standard  output  in  a
                     form  that  can  be  used  as  shell  input.   If  +p is specified, then the values are not
                     displayed.
              -r     The given vnames are marked read-only and these  names  cannot  be  changed  by  subsequent
                     assignment.
              -s     When given along with -i, restricts integer size to short.
              -t     Tags the variables.  Tags are user definable and have no special meaning to the shell.
              -u     When  given along with -i, specifies unsigned integer.  Otherwise, all lowercase characters
                     are converted to uppercase.  The lowercase option, -l, is turned  off.   Equivalent  to  -M
                     toupper .
              -x     The  given  vnames  are  marked  for  automatic  export to the environment of subsequently-
                     executed commands.  Variables whose names contain a .  cannot be exported.

              The -i, -F, -E, and -X options cannot be specified along with -R, -L, or -Z.  The -b option cannot
              be  specified  along  with  -L, -u, or -l.  The -f, -m, -n, and -T options cannot be used together
              with any other option.

              Using + rather than - causes these options to be turned off.  If no vname arguments are  given,  a
              list  of  vnames  (and optionally the values) of the variables is printed.  (Using + rather than -
              keeps the values from being printed.)  The -p option causes typeset followed by the option letters
              to  be printed before each name rather than the names of the options.  If any option other than -p
              is given, only those variables which have all of the given options are  printed.   Otherwise,  the
              vnames and attributes of all variables that have attributes are printed.

       ulimit [ -HSaMctdfxlqenupmrbiswTv ] [ limit ]
              Set or display a resource limit.  The available resource limits are listed below.  Many systems do
              not support one or more of these limits.  The limit for a specified resource is set when limit  is
              specified.   The value of limit can be a number in the unit specified below with each resource, or
              the value unlimited.  The -H and -S options specify whether the hard limit or the soft  limit  for
              the  given resource is set.  A hard limit cannot be increased once it is set.  A soft limit can be
              increased up to the value of the hard limit.  If neither the H nor  S  option  is  specified,  the
              limit  applies  to  both.   The  current resource limit is printed when limit is omitted.  In this
              case, the soft limit is printed unless H is specified.  When more than one resource is  specified,
              then the limit name and unit is printed before the value.
              -a     Lists all of the current resource limits.
              -b     The socket buffer size in bytes.
              -c     The number of 512-byte blocks on the size of core dumps.
              -d     The number of K-bytes on the size of the data area.
              -e     The scheduling priority.
              -f     The  number  of  512-byte  blocks on files that can be written by the current process or by
                     child processes (files of any size may be read).
              -i     The signal queue size.
              -l     The locked address space in K-bytes.
              -M     The address space limit in K-bytes.
              -m     The number of K-bytes on the size of physical memory.
              -n     The number of file descriptors plus 1.
              -p     The number of 512-byte blocks for pipe buffering.
              -q     The message queue size in K-bytes.
              -r     The max real-time priority.
              -s     The number of K-bytes on the size of the stack area.
              -T     The number of threads.
              -t     The number of CPU seconds to be used by each process.
              -u     The number of processes.
              -v     The number of K-bytes for virtual memory.
              -w     The swap size in K-bytes.
              -x     The number of file locks.

              If no option is given, -f is assumed.

       umask [ -S ] [ mask ]
              The user file-creation mask is set to mask (see umask(2)).  mask can either be an octal number  or
              a  symbolic  value as described in chmod(1).  If a symbolic value is given, the new umask value is
              the complement of the result of applying mask to the complement of the previous umask  value.   If
              mask  is  omitted,  the current value of the mask is printed.  The -S option causes the mode to be
              printed as a symbolic value.  Otherwise, the mask is printed in octal.

       unalias [ -a ] name ...
              The aliases given by the list of names are removed from the alias list.  The -a option causes  all
              the aliases to be unset.

       † unset [ -fnv ] vname ...
              The  variables  given by the list of vnames are unassigned, i.e., except for subvariables within a
              type, their values and attributes are erased.  For subvariables of a type, the values are reset to
              the default value from the type definition.  Readonly variables cannot be unset.  If the -f option
              is set, then the names refer to function names.  If the -v option is set, then the names refer  to
              variable names.  The -f option overrides -v.  If -n is set and name is a name reference, then name
              will be unset rather than the variable that it references.   The  default  is  equivalent  to  -v.
              Unsetting  LINENO,  MAILCHECK, OPTARG, OPTIND, RANDOM, SECONDS, TMOUT, and _ removes their special
              meaning even if they are subsequently assigned to.

       wait [ job ... ]
              Wait for the specified job and report its termination status.  If  job  is  not  given,  then  all
              currently active child processes are waited for.  The exit status from this command is that of the
              last process waited for if job is specified; otherwise it is zero.  See Jobs for a description  of
              the format of job.

       whence [ -afpqv ] name ...
              For each name, indicate how it would be interpreted if used as a command name.
              The  -v option produces a more verbose report.  The -f option skips the search for functions.  The
              -p option does a path search for name even if name is an alias, a function, or  a  reserved  word.
              The  -p  option turns off the -v option.  The -q option causes whence to enter quiet mode.  whence
              will return zero if all arguments are built-ins, functions, or are programs  found  on  the  path.
              The  -a  option is similar to the -v option but causes all interpretations of the given name to be
              reported.

   Invocation.
       If the shell is invoked by exec(2), initialization depends on argument zero  ($0)  as  follows.   If  the
       first  character  of $0 is -, or the -l option is given on the invocation command line, then the shell is
       assumed to be a login shell.  If the basename of the command path in $0 is rsh, rksh, or krsh,  then  the
       shell  becomes  restricted.   If  the  basename  is  sh  or  rsh,  or the -o posix option is given on the
       invocation command line, then the shell is initialized in full POSIX compliance mode (see the set builtin
       command  above for more information).  After this, if the shell was assumed to be a login shell, commands
       are read from /etc/profile and then from $HOME/.profile if  it  exists.   Alternatively,  the  option  -l
       causes  the  shell  to be treated as a login shell.  Next, for interactive shells, commands are read from
       the file named by ENV if the file exists, its name being determined by  performing  parameter  expansion,
       command  substitution,  and  arithmetic  expansion  on the value of that environment variable.  If the -s
       option is not present and arg and a file by the name of arg exists,  then  it  reads  and  executes  this
       script.  Otherwise, if the first arg does not contain a /, a path search is performed on the first arg to
       determine the name of the script to execute.  The script arg must have execute permission and any  setuid
       and  setgid  settings will be ignored.  If the script is not found on the path, arg is processed as if it
       named a built-in command or function.  Commands are then read as described below; the  following  options
       are interpreted by the shell when it is invoked:

       -D      A  list  of all double quoted strings that are preceded by a $ will be printed on standard output
               and the shell will exit.  This set of strings will be subject to language  translation  when  the
               locale is not C or POSIX.  No commands will be executed.

       -E or -o rc or --rc
               Read the file named by the ENV variable or by $HOME/.kshrc if not defined after the profiles.  On
               by default for interactive shells. Use +E, +o rc or --norc to turn off.

       -c      Read and execute a script from the first arg instead of a file.   The  second  arg,  if  present,
               becomes that script's command name ($0).  Any third and further args become positional parameters
               starting at $1.

       -s      Read and execute a script from standard input instead of a file.  The command name ($0) cannot be
               set.   Any  args become the positional parameters starting at $1.  This option is forced on if no
               arg is given and is ignored if -c is also specified.

       -i or -o interactive or --interactive
               If the -i option is present or if the shell's standard input and standard error are attached to a
               terminal (as told by tcgetattr(3)), then this shell is interactive.  In this case TERM is ignored
               (so that kill 0 does not kill an interactive shell) and INTR is caught and ignored (so that  wait
               is interruptible).  In all cases, QUIT is ignored by the shell.

       -r or -o restricted or --restricted
               If the -r option is present, the shell is a restricted shell.

       The  remaining  options  and  arguments  are described under the set command above.  An optional - as the
       first argument is ignored.

   Rksh Only.
       Rksh is used to set up login names and execution environments whose capabilities are more controlled than
       those  of  the  standard  shell.   The  actions  of  rksh  are identical to those of ksh, except that the
       following are disallowed:
              unsetting the restricted option,
              changing directory (see cd(1)),
              setting or unsetting the value or attributes of SHELL, ENV, FPATH, or PATH,
              specifying path or command names containing /,
              redirecting output (>, >|, <>, and >>),
              adding or deleting built-in commands,
              using command -p to invoke a command.

       The restrictions above are enforced after .profile and the ENV files are interpreted.

       When a command to be executed is found to be a shell procedure, rksh invokes ksh to execute it.  Thus, it
       is  possible  to  provide  to  the  end-user  shell  procedures that have access to the full power of the
       standard shell, while imposing a limited menu of commands; this scheme assumes that the end-user does not
       have write and execute permissions in the same directory.

       The  net effect of these rules is that the writer of the .profile has complete control over user actions,
       by performing guaranteed setup actions and leaving the user in an appropriate directory (probably not the
       login directory).

       The  system  administrator  often  sets  up  a directory of commands (e.g., /usr/rbin) that can be safely
       invoked by rksh.

EXIT STATUS

       Errors detected by the shell, such as syntax errors, cause the shell to return a  non-zero  exit  status.
       If  the  shell  is being used non-interactively, then execution of the shell file is abandoned unless the
       error occurs inside a subshell in which case the subshell is abandoned.  Otherwise, the shell returns the
       exit  status of the last command executed (see also the exit command above).  Run time errors detected by
       the shell are reported by printing the command or function name and the error  condition.   If  the  line
       number  that  the  error  occurred on is greater than one, then the line number is also printed in square
       brackets ([]) after the command or function name.

FILES

       /etc/profile
              The system wide initialization file, executed for login shells.

       $HOME/.profile
              The personal initialization file, executed for login shells after /etc/profile.

       $HOME/.kshrc
              Default personal initialization file, executed for interactive shells when ENV is not set.

       /etc/suid_profile
              Alternative initialization file, executed instead of the personal  initialization  file  when  the
              real and effective user or group id do not match.

       /dev/null
              NULL device

SEE ALSO

       cat(1),  cd(1),  chmod(1),  cut(1),  date(1),  egrep(1),  echo(1),  emacs(1), env(1), fgrep(1), gmacs(1),
       grep(1), stty(1), test(1), umask(1), vi(1), dup(2), exec(2), fork(2),  getpwnam(3),  ioctl(2),  lseek(2),
       paste(1),  pathconf(2),  pipe(2),  sysconf(3),  umask(2),  ulimit(2),  wait(2),  strftime(3), wctrans(3),
       rand(3), profile(5), environ(7).

       Morris I. Bolsky and David G. Korn, The New KornShell Command and Programming  Language,  Prentice  Hall,
       1995.

       POSIX - Part 2: Shell and Utilities, IEEE Std 1003.2-1992, ISO/IEC 9945-2, IEEE, 1993.

CAVEATS

       If a command is executed, and then a command with the same name is installed in a directory in the search
       path before the directory where the original command was found, the  shell  will  continue  to  exec  the
       original command.  Use the hash command or the -t option of the alias command to correct this situation.

       Some very old shell scripts contain a ^ as a synonym for the pipe character |.

       Using  the hist built-in command within a compound command will cause the whole command to disappear from
       the history file.

       The built-in command . file reads the whole file before any commands are executed.  Therefore, alias  and
       unalias commands in the file will not apply to any commands defined in the file.

       Traps  are  not processed while a job is waiting for a foreground process.  Thus, a trap on CHLD won't be
       executed until the foreground job terminates.

       It is a good idea to leave a space after the comma operator in  arithmetic  expressions  to  prevent  the
       comma from being interpreted as the decimal point character in certain locales.

                                                                                                          KSH(1)