FC(P) POSIX Programmer's Manual FC(P)NAMEfc - process the command history list
SYNOPSISfc [-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 pre‐
viously 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 num‐
ber 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 exe‐
cuted, 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 re‐
direction 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 vari‐
able (see the Base Definitions volume of IEEE Std 1003.1-2001,
Chapter 8, Environment Variables). The value in the FCEDIT vari‐
able 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 edi‐
tor on them. The commands shall be written in the sequence indi‐
cated 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 com‐
mands 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 exe‐
cuted 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 com‐
mand 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 pre‐
senting 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 HIST‐
FILE 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 ini‐
tializing 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. There‐
fore, it is implementation-defined whether changes made to HIST‐
FILE 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 implemen‐
tation-defined. If more than one instance of the shell is using
the same history file, it is unspecified how updates to the his‐
tory 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 his‐
tory 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 Vari‐
ables 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 edi‐
tor, 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 his‐
tory 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 interac‐
tion 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 effec‐
tively 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 com‐
mand line editing feature in sh. For example, in vi editing mode, typ‐
ing "<ESC> v" is equivalent to:
EDITOR=vi fc
However, the fc utility allows the user the flexibility to edit multi‐
ple 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 - (equiva‐
lent 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 cre‐
ate 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 exe‐
cution, 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 .
IEEE/The Open Group 2003 FC(P)
