FC(1)                      POSIX Programmer's Manual                     FC(1)



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

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
       POSIX.1-2017, 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
                 POSIX.1-2017, 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 <equals-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 POSIX.1-2017, Section 8.2, Internationalization
                 Variables for the precedence of internationalization
                 variables used to determine the values of locale categories.)

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

       LC__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 ""<<EESSCC>>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 rr (``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

       The Base Definitions volume of POSIX.1-2017, Chapter _8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

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

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



IEEE/The Open Group                  2017                                FC(1)
