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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 differ (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  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
              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 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(1P)
 

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