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NAME
fc - process the command history list
SYNOPSIS
fc [-r][-e editor] [first[last]]
fc -l[-nr] [first[last]]
fc -s[old=new][first]
DESCRIPTION
The fc utility shall list, or shall edit and re-execute, commands previously entered to an
interactive sh.
The command history list shall reference commands by number. The first number in the list
is selected arbitrarily. The relationship of a number to its command shall not change
except when the user logs in and no other process is accessing the list, at which time the
system may reset the numbering to start the oldest retained command at another number
(usually 1). When the number reaches an implementation-defined upper limit, which shall be
no smaller than the value in HISTSIZE or 32767 (whichever is greater), the shell may wrap
the numbers, starting the next command with a lower number (usually 1). However, despite
this optional wrapping of numbers, fc shall maintain the time-ordering sequence of the
commands. For example, if four commands in sequence are given the numbers 32766, 32767, 1
(wrapped), and 2 as they are executed, command 32767 is considered the command previous to
1, even though its number is higher.
When commands are edited (when the -l option is not specified), the resulting lines shall
be entered at the end of the history list and then re-executed by sh. The fc command that
caused the editing shall not be entered into the history list. If the editor returns a
non-zero exit status, this shall suppress the entry into the history list and the command
re-execution. Any command line variable assignments or redirection operators used with fc
shall affect both the fc command itself as well as the command that results; for example:
fc -s -- -1 2>/dev/null
reinvokes the previous command, suppressing standard error for both fc and the previous
command.
OPTIONS
The fc utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001,
Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
-e editor
Use the editor named by editor to edit the commands. The editor string is a utility
name, subject to search via the PATH variable (see the Base Definitions volume of
IEEE Std 1003.1-2001, Chapter 8, Environment Variables). The value in the FCEDIT
variable shall be used as a default when -e is not specified. If FCEDIT is null or
unset, ed shall be used as the editor.
-l (The letter ell.) List the commands rather than invoking an editor on them. The
commands shall be written in the sequence indicated by the first and last operands,
as affected by -r, with each command preceded by the command number.
-n Suppress command numbers when listing with -l.
-r Reverse the order of the commands listed (with -l) or edited (with neither -l nor
-s).
-s Re-execute the command without invoking an editor.
OPERANDS
The following operands shall be supported:
first, last
Select the commands to list or edit. The number of previous commands that can be
accessed shall be determined by the value of the HISTSIZE variable. The value of
first or last or both shall be one of the following:
[+]number
A positive number representing a command number; command numbers can be displayed
with the -l option.
-number
A negative decimal number representing the command that was executed number of
commands previously. For example, -1 is the immediately previous command.
string
A string indicating the most recently entered command that begins with that string.
If the old= new operand is not also specified with -s, the string form of the first
operand cannot contain an embedded equal sign.
When the synopsis form with -s is used:
* If first is omitted, the previous command shall be used.
For the synopsis forms without -s:
* If last is omitted, last shall default to the previous command when -l is
specified; otherwise, it shall default to first.
* If first and last are both omitted, the previous 16 commands shall be listed or
the previous single command shall be edited (based on the -l option).
* If first and last are both present, all of the commands from first to last shall
be edited (without -l) or listed (with -l). Editing multiple commands shall be
accomplished by presenting to the editor all of the commands at one time, each
command starting on a new line. If first represents a newer command than last,
the commands shall be listed or edited in reverse sequence, equivalent to using
-r. For example, the following commands on the first line are equivalent to the
corresponding commands on the second:
fc -r 10 20 fc 30 40
fc 20 10 fc -r 40 30
* When a range of commands is used, it shall not be an error to specify first or
last values that are not in the history list; fc shall substitute the value
representing the oldest or newest command in the list, as appropriate. For
example, if there are only ten commands in the history list, numbered 1 to 10:
fc -l
fc 1 99
shall list and edit, respectively, all ten commands.
old=new
Replace the first occurrence of string old in the commands to be re-executed by the
string new.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of fc:
FCEDIT This variable, when expanded by the shell, shall determine the default value for
the -e editor option's editor option-argument. If FCEDIT is null or unset, ed shall
be used as the editor.
HISTFILE
Determine a pathname naming a command history file. If the HISTFILE variable is not
set, the shell may attempt to access or create a file .sh_history in the directory
referred to by the HOME environment variable. If the shell cannot obtain both read
and write access to, or create, the history file, it shall use an unspecified
mechanism that allows the history to operate properly. (References to history
"file" in this section shall be understood to mean this unspecified mechanism in
such cases.) An implementation may choose to access this variable only when
initializing the history file; this initialization shall occur when fc or sh first
attempt to retrieve entries from, or add entries to, the file, as the result of
commands issued by the user, the file named by the ENV variable, or implementation-
defined system start-up files. In some historical shells, the history file is
initialized just after the ENV file has been processed. Therefore, it is
implementation-defined whether changes made to HISTFILE after the history file has
been initialized are effective. Implementations may choose to disable the history
list mechanism for users with appropriate privileges who do not set HISTFILE ; the
specific circumstances under which this occurs are implementation-defined. If more
than one instance of the shell is using the same history file, it is unspecified
how updates to the history file from those shells interact. As entries are deleted
from the history file, they shall be deleted oldest first. It is unspecified when
history file entries are physically removed from the history file.
HISTSIZE
Determine a decimal number representing the limit to the number of previous
commands that are accessible. If this variable is unset, an unspecified default
greater than or equal to 128 shall be used. The maximum number of commands in the
history list is unspecified, but shall be at least 128. An implementation may
choose to access this variable only when initializing the history file, as
described under HISTFILE . Therefore, it is unspecified whether changes made to
HISTSIZE after the history file has been initialized are effective.
LANG Provide a default value for the internationalization variables that are unset or
null. (See the Base Definitions volume of IEEE Std 1003.1-2001, Section 8.2,
Internationalization Variables for the precedence of internationalization variables
used to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of all the other
internationalization variables.
LC_CTYPE
Determine the locale for the interpretation of sequences of bytes of text data as
characters (for example, single-byte as opposed to multi-byte characters in
arguments and input files).
LC_MESSAGES
Determine the locale that should be used to affect the format and contents of
diagnostic messages written to standard error.
NLSPATH
Determine the location of message catalogs for the processing of LC_MESSAGES .
ASYNCHRONOUS EVENTS
Default.
STDOUT
When the -l option is used to list commands, the format of each command in the list shall
be as follows:
"%d\t%s\n", <line number>, <command>
If both the -l and -n options are specified, the format of each command shall be:
"\t%s\n", <command>
If the <command> consists of more than one line, the lines after the first shall be
displayed as:
"\t%s\n", <continued-command>
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 Successful completion of the listing.
>0 An error occurred.
Otherwise, the exit status shall be that of the commands executed by fc.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
Since editors sometimes use file descriptors as integral parts of their editing,
redirecting their file descriptors as part of the fc command can produce unexpected
results. For example, if vi is the FCEDIT editor, the command:
fc -s | more
does not work correctly on many systems.
Users on windowing systems may want to have separate history files for each window by
setting HISTFILE as follows:
HISTFILE=$HOME/.sh_hist$$
EXAMPLES
None.
RATIONALE
This utility is based on the fc built-in of the KornShell.
An early proposal specified the -e option as [-e editor [ old = new ]], which is not
historical practice. Historical practice in fc of either [-e editor ] or [-e - [ old = new
]] is acceptable, but not both together. To clarify this, a new option -s was introduced
replacing the [-e -]. This resolves the conflict and makes fc conform to the Utility
Syntax Guidelines.
HISTFILE
Some implementations of the KornShell check for the superuser and do not create a
history file unless HISTFILE is set. This is done primarily to avoid creating
unlinked files in the root file system when logging in during single-user mode.
HISTFILE must be set for the superuser to have history.
HISTSIZE
Needed to limit the size of history files. It is the intent of the standard
developers that when two shells share the same history file, commands that are
entered in one shell shall be accessible by the other shell. Because of the
difficulties of synchronization over a network, the exact nature of the interaction
is unspecified.
The initialization process for the history file can be dependent on the system start-up
files, in that they may contain commands that effectively preempt the settings the user
has for HISTFILE and HISTSIZE . For example, function definition commands are recorded in
the history file. If the system administrator includes function definitions in some system
start-up file called before the ENV file, the history file is initialized before the user
can influence its characteristics. In some historical shells, the history file is
initialized just after the ENV file has been processed. Because of these situations, the
text requires the initialization process to be implementation-defined.
Consideration was given to omitting the fc utility in favor of the command line editing
feature in sh. For example, in vi editing mode, typing "<ESC> v" is equivalent to:
EDITOR=vi fc
However, the fc utility allows the user the flexibility to edit multiple commands
simultaneously (such as fc 10 20) and to use editors other than those supported by sh for
command line editing.
In the KornShell, the alias r (``re-do") is preset to fc -e - (equivalent to the POSIX fc
-s). This is probably an easier command name to remember than fc (``fix command"), but it
does not meet the Utility Syntax Guidelines. Renaming fc to hist or redo was considered,
but since this description closely matches historical KornShell practice already, such a
renaming was seen as gratuitous. Users are free to create aliases whenever odd historical
names such as fc, awk, cat, grep, or yacc are standardized by POSIX.
Command numbers have no ordering effects; they are like serial numbers. The -r option and
-number operand address the sequence of command execution, regardless of serial numbers.
So, for example, if the command number wrapped back to 1 at some arbitrary point, there
would be no ambiguity associated with traversing the wrap point. For example, if the
command history were:
32766: echo 1
32767: echo 2
1: echo 3
the number -2 refers to command 32767 because it is the second previous command,
regardless of serial number.
FUTURE DIRECTIONS
None.
SEE ALSO
sh
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee document. The
original Standard can be obtained online at http://www.opengroup.org/unix/online.html .