Originální popis anglicky:
fc - process the command history list
Návod, kniha: POSIX Programmer's Manual
fc [-r][-e editor]
[first [last]]
fc -l
[-nr]
[first
[last]]
fc -s
[old=new][
first]
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:
reinvokes the previous command, suppressing standard error for both
fc
and the previous command.
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 variable (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
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.
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
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:
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.
Not used.
None.
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
IEEE Std 1003.1-2001, 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 .
Default.
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:
If the <
command> consists of more than one line, the lines after
the first shall be displayed as:
"\t%s\n", <continued-command>
The standard error shall be used only for diagnostic messages.
None.
None.
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.
Default.
The following sections are informative.
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:
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$$
None.
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
"<ESC> v" is equivalent to:
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 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.
None.
sh
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
.
