Man Pages

fc(1p) - phpMan fc(1p) - phpMan

Command: man perldoc info search(apropos)  


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



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

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 arbitrar-
       ily. 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  com-
       mand 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 Syn-
       tax 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, Envi-
              ronment Variables). The value in the FCEDIT variable shall be used as a default when -e  is  not  speci-
              fied. 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 writ-
              ten in the sequence indicated by the first and last operands, as affected by -r, with each command  pre-
              ceded 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  com-
                 mands 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 imple-
              mentation may choose to access this variable only when initializing the history file;  this  initializa-
              tion  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  circum-
              stances  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  inter-
              act.  As  entries are deleted from the history file, they shall be deleted oldest first.  It is unspeci-
              fied 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  accessi-
              ble.  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 implementa-
              tion  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  prece-
              dence 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  exam-
              ple, 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 writ-
              ten 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  fol-
       lows:


              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. His-
       torical 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 con-
       form 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  Guide-
       lines.  Renaming fc to hist or redo was considered, but since this description closely matches historical Korn-
       Shell 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, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, 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(1P)