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

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 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
       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 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
       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  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)

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