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xargs.1: further editing improvements

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* xargs/xargs.1: Start new sentences on a new line.
Use '\~' as unbreakable space in "2048 bytes".
This commit is contained in:
Bernhard Voelker 2023-09-23 16:24:40 +02:00
parent a77c161b65
commit c2002a3646
1 changed files with 105 additions and 84 deletions
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189
xargs/xargs.1
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@ -21,8 +21,8 @@ and executes the
.IR echo )
one or more times with any
.I initial-arguments
followed by items read from standard input. Blank lines on the
standard input are ignored.
followed by items read from standard input.
Blank lines on the standard input are ignored.
.P
The command line for
.I command
@ -30,14 +30,15 @@ is built up until it reaches a system-defined limit (unless the
.B \-n
and
.B \-L
options are used). The specified
options are used).
The specified
.I command
will be invoked as many times as necessary to use up the list of input
items. In general, there will be many fewer invocations of
will be invoked as many times as necessary to use up the list of input items.
In general, there will be many fewer invocations of
.I command
than there were items in the input. This will normally have
significant performance benefits. Some commands can usefully be
executed in parallel too; see the
than there were items in the input.
This will normally have significant performance benefits.
Some commands can usefully be executed in parallel too; see the
.B \-P
option.
.P
@ -52,8 +53,8 @@ prevents such problems.
When using this option you will need to
ensure that the program which produces the input for
.B xargs
also uses a null character as a separator. If that program is
GNU
also uses a null character as a separator.
If that program is GNU
.B find
for example, the
.B \-print0
@ -61,46 +62,46 @@ option does this for you.
.P
If any invocation of the command exits with a status of 255,
.B xargs
will stop immediately without reading any further input. An error
message is issued on stderr when this happens.
will stop immediately without reading any further input.
An error message is issued on stderr when this happens.
.
.SH OPTIONS
.TP
.B \-0, \-\-null
Input items are terminated by a null character instead of by
whitespace, and the quotes and backslash are not special (every
character is taken literally). Disables the end-of-file string, which
is treated like any other argument. Useful when input items might
contain white space, quote marks, or backslashes. The GNU find
\-print0 option produces input suitable for this mode.
character is taken literally).
Disables the end-of-file string, which is treated like any other argument.
Useful when input items might contain white space, quote marks, or backslashes.
The GNU find \-print0 option produces input suitable for this mode.
.TP
.BI "\-a " file ", \-\-arg\-file=" file
Read items from
.I file
instead of standard input. If you use this option, stdin remains
unchanged when commands are run. Otherwise, stdin is redirected
from
instead of standard input.
If you use this option, stdin remains unchanged when commands are run.
Otherwise, stdin is redirected from
.IR /dev/null .
.TP
.BI "\-\-delimiter=" delim ", \-d" " delim"
Input items are terminated by the specified character. The specified
delimiter may be a single character, a C-style character escape such
Input items are terminated by the specified character.
The specified delimiter may be a single character, a C-style character escape such
as
.BR \en ,
or an octal or hexadecimal escape code. Octal and hexadecimal
escape codes are understood as for the
or an octal or hexadecimal escape code.
Octal and hexadecimal escape codes are understood as for the
.B printf
command.
Multibyte characters are not supported.
When processing the input,
quotes and backslash are not special;
When processing the input, quotes and backslash are not special;
every character in the input is taken literally.
The
.B \-d
option disables any end-of-file string, which is treated like any
other argument. You can use this option when the input consists of
other argument.
You can use this option when the input consists of
simply newline-separated items, although it is almost always better to
design your program to use
.B \-\-null
@ -108,7 +109,8 @@ where this is possible.
.TP
.BI \-E " eof-str"
Set the end-of-file string to \fIeof-str\fR. If the end-of-file
Set the end-of-file string to \fIeof-str\fR.
If the end-of-file
string occurs as a line of input, the rest of the input is ignored.
If neither
.B \-E
@ -119,11 +121,13 @@ is used, no end-of-file string is used.
.BR \-e "[\fIeof-str\fR], " "\-\-eof" [\fI=eof-str\fR]
This option is a synonym for the
.B \-E
option. Use
option.
Use
.B \-E
instead,
because it is POSIX compliant while this option is not. If
\fIeof-str\fR is omitted, there is no end-of-file string. If neither
because it is POSIX compliant while this option is not.
If \fIeof-str\fR is omitted, there is no end-of-file string.
If neither
.B \-E
nor
.B \-e
@ -131,7 +135,8 @@ is used, no end-of-file string is used.
.TP
.BI \-I " replace-str"
Replace occurrences of \fIreplace-str\fR in the initial-arguments with
names read from standard input. Also, unquoted blanks do not
names read from standard input.
Also, unquoted blanks do not
terminate input items; instead the separator is the newline character.
Implies
.B \-x
@ -144,7 +149,8 @@ This option is a synonym for
.BI \-I replace-str
if
.I replace-str
is specified. If the
is specified.
If the
.I replace-str
argument is missing, the effect is the same as
.BR \-I {}.
@ -155,26 +161,31 @@ instead.
.BI \-L " max-lines"
Use at most \fImax-lines\fR nonblank input lines per command line.
Trailing blanks cause an input line to be logically continued on the
next input line. Implies
next input line.
Implies
.BR \-x .
.TP
.BR \-l "[\fImax-lines\fR], " \-\-max-lines "[=\fImax-lines\fR]"
Synonym for the
.B \-L
option. Unlike
option.
Unlike
.BR \-L ,
the
.I max-lines
argument is optional. If
argument is optional.
If
.I max-lines
is not specified, it defaults to one. The
is not specified, it defaults to one.
The
.B \-l
option is deprecated since the POSIX standard specifies
.B \-L
instead.
.TP
.BI \-n " max-args\fR, \fI" "\-\-max\-args" \fR=\fImax-args
Use at most \fImax-args\fR arguments per command line. Fewer than
Use at most \fImax-args\fR arguments per command line.
Fewer than
.I max-args
arguments will be used if the size (see the
.B \-s
@ -187,12 +198,13 @@ will exit.
.BI \-P " max-procs\fR, \fI" \-\-max\-procs "\fR=\fImax-procs"
Run up to
.I max-procs
processes at a time; the default is 1. If
processes at a time; the default is 1.
If
.I max-procs
is 0,
.B xargs
will run as many processes as
possible at a time. Use the
will run as many processes as possible at a time.
Use the
.B \-n
option or the
.B \-L
@ -203,9 +215,10 @@ While
.B xargs
is running, you can send its process a SIGUSR1 signal to increase the
number of commands to run simultaneously, or a SIGUSR2 to decrease the
number. You cannot increase it above an implementation-defined limit
(which is shown with \-\-show-limits). You cannot decrease it below
1.
number.
You cannot increase it above an implementation-defined limit
(which is shown with \-\-show-limits).
You cannot decrease it below 1.
.B xargs
never terminates its commands; when asked to decrease, it merely
waits for more than one existing command to terminate before starting
@ -213,12 +226,14 @@ another.
.B Please note
that it is up to the called processes to properly manage parallel
access to shared resources. For example, if more than one of them
tries to print to stdout, the output will be produced in an
indeterminate order (and very likely mixed up) unless the processes
collaborate in some way to prevent this. Using some kind of locking
scheme is one way to prevent such problems. In general, using a
locking scheme will help ensure correct output but reduce performance.
access to shared resources.
For example, if more than one of them tries to print to stdout,
the output will be produced in an indeterminate order (and very
likely mixed up) unless the processes collaborate in some way to
prevent this.
Using some kind of locking scheme is one way to prevent such problems.
In general, using a locking scheme will help ensure correct output
but reduce performance.
If you don't want to tolerate the performance difference, simply
arrange for each process to produce a separate output file (or
otherwise use separate resources).
@ -226,37 +241,41 @@ otherwise use separate resources).
.B \-o, \-\-open\-tty
Reopen stdin as
.I /dev/tty
in the child process before executing the command. This is useful if
you want
in the child process before executing the command.
This is useful if you want
.B xargs
to run an interactive application.
.TP
.B \-p, \-\-interactive
Prompt the user about whether to run each command line and read a line
from the terminal. Only run the command line if the response starts
with `y' or `Y'. Implies
from the terminal.
Only run the command line if the response starts with `y' or `Y'.
Implies
.BR \-t .
.TP
.BR \-\-process\-slot\-var "=\fIname\fR"
Set the environment variable
.I name
to a unique value in each running child process. Values are reused
once child processes exit. This can be used in a rudimentary load
distribution scheme, for example.
to a unique value in each running child process.
Values are reused once child processes exit.
This can be used in a rudimentary load distribution scheme, for example.
.TP
.B \-r, \-\-no\-run\-if\-empty
If the standard input does not contain any nonblanks, do not run the
command. Normally, the command is run once even if there is no input.
command.
Normally, the command is run once even if there is no input.
This option is a GNU extension.
.TP
.BI \-s " max-chars\fR, \fI" \-\-max\-chars "=\fImax-chars\fR"
Use at most \fImax-chars\fR characters per command line, including the
command and initial-arguments and the terminating nulls at the ends of
the argument strings. The largest allowed value is system-dependent,
and is calculated as the argument length limit for exec, less the size
of your environment, less 2048 bytes of headroom. If this value is
more than 128\~KiB, 128\~KiB is used as the default value; otherwise, the
default value is the maximum. 1\~KiB is 1024 bytes.
the argument strings.
The largest allowed value is system-dependent, and is calculated as the
argument length limit for exec, less the size of your environment,
less 2048\~bytes of headroom.
If this value is more than 128\~KiB, 128\~KiB is used as the default value;
otherwise, the default value is the maximum.
1\~KiB is 1024 bytes.
.B xargs
automatically adapts to tighter constraints.
.TP
@ -266,7 +285,8 @@ operating system,
.BR xargs '
choice of buffer size and the
.B \-s
option. Pipe the input from
option.
Pipe the input from
.I /dev/null
(and perhaps specify
.BR \-\-no-run-if-empty )
@ -284,8 +304,8 @@ Exit if the size (see the
option) is exceeded.
.TP
.B "\-\-"
Delimit the option list. Later arguments, if any, are treated as operands even
if they begin with
Delimit the option list.
Later arguments, if any, are treated as operands even if they begin with
.IR \- .
For example,
.B xargs \-\- \-\-help
@ -318,8 +338,7 @@ and
.B \-\-max-args
(\fB\-n\fP)
are mutually exclusive.
If some of them are specified at the same time,
then
If some of them are specified at the same time, then
.B xargs
will generally use the option specified last on the command line,
i.e., it will reset the value of the offending option (given before)
@ -351,7 +370,8 @@ Find files named
.B core
in or below the directory
.B /tmp
and delete them. Note that this will work incorrectly if there are
and delete them.
Note that this will work incorrectly if there are
any filenames containing newlines or spaces.
.P
.B find /tmp \-name core \-type f \-print0 | xargs \-0 /bin/rm \-f
@ -415,8 +435,8 @@ a program died due to a fatal signal.
.SH "STANDARDS CONFORMANCE"
As of GNU xargs version 4.2.9, the default behaviour of
.B xargs
is not to have a logical end-of-file marker. POSIX (IEEE Std 1003.1,
2004 Edition) allows this.
is not to have a logical end-of-file marker.
POSIX (IEEE Std 1003.1, 2004 Edition) allows this.
.P
The \-l and \-i options appear in the 1997 version of the POSIX
standard, but do not appear in the 2004 version of the standard.
@ -428,10 +448,12 @@ compatibility with BSD.
The POSIX standard allows implementations to have a limit on the size
of arguments to the
.B exec
functions. This limit could be as low as 4096 bytes including the size of the
environment. For scripts to be portable, they must not rely on a
larger value. However, I know of no implementation whose actual limit
is that small. The
functions.
This limit could be as low as 4096 bytes including the size of the
environment.
For scripts to be portable, they must not rely on a larger value.
However, I know of no implementation whose actual limit is that small.
The
.B \-\-show\-limits
option can be used to discover the actual limits in force on the
current system.
@ -452,14 +474,16 @@ to be used securely, since there will always be a time gap between the
production of the list of input files and their use in the commands
that
.B xargs
issues. If other users have access to the system, they can manipulate
issues.
If other users have access to the system, they can manipulate
the filesystem during this time window to force the action of the
commands
.B xargs
runs to apply to files that you didn't intend. For a more detailed
discussion of this and related problems, please refer to the
``Security Considerations'' chapter in the findutils Texinfo
documentation. The
runs to apply to files that you didn't intend.
For a more detailed discussion of this and related problems, please refer
to the ``Security Considerations'' chapter in the findutils Texinfo
documentation.
The
.B \-execdir
option of
.B find
@ -467,11 +491,8 @@ can often be used as a more secure alternative.
When you use the
.B \-I
option,
each line read from the input is buffered
internally.
This means that there is an upper limit on the length
of input line that
option, each line read from the input is buffered internally.
This means that there is an upper limit on the length of input line that
.B xargs
will accept when used with the
.B \-I