freebsd-skq/usr.bin/xargs/xargs.1

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.\"	@(#)xargs.1	8.1 (Berkeley) 6/6/93
.\" $FreeBSD$
.\" $xMach: xargs.1,v 1.2 2002/02/23 05:23:37 tim Exp $
.\"
.Dd September 21, 2020
.Dt XARGS 1
.Os
.Sh NAME
.Nm xargs
.Nd "construct argument list(s) and execute utility"
.Sh SYNOPSIS
.Nm
.Op Fl 0oprt
.Op Fl E Ar eofstr
.Oo
.Fl I Ar replstr
.Op Fl R Ar replacements
.Op Fl S Ar replsize
.Oc
.Op Fl J Ar replstr
.Op Fl L Ar number
.Oo
.Fl n Ar number
.Op Fl x
.Oc
.Op Fl P Ar maxprocs
.Op Fl s Ar size
.Op Ar utility Op Ar argument ...
.Sh DESCRIPTION
The
.Nm
utility reads space, tab, newline and end-of-file delimited strings
from the standard input and executes
.Ar utility
with the strings as
arguments.
.Pp
Any arguments specified on the command line are given to
.Ar utility
upon each invocation, followed by some number of the arguments read
from the standard input of
.Nm .
This is repeated until standard input is exhausted.
.Pp
Spaces, tabs and newlines may be embedded in arguments using single
(``\ '\ '')
or double (``"'') quotes or backslashes (``\e'').
Single quotes escape all non-single quote characters, excluding newlines,
up to the matching single quote.
Double quotes escape all non-double quote characters, excluding newlines,
up to the matching double quote.
Any single character, including newlines, may be escaped by a backslash.
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl 0 , Fl -null
Change
.Nm
to expect NUL
(``\\0'')
characters as separators, instead of spaces and newlines.
This is expected to be used in concert with the
.Fl print0
function in
.Xr find 1 .
.It Fl E Ar eofstr
Use
.Ar eofstr
as a logical EOF marker.
.It Fl I Ar replstr
Execute
.Ar utility
for each input line, replacing one or more occurrences of
.Ar replstr
in up to
.Ar replacements
(or 5 if no
.Fl R
flag is specified) arguments to
.Ar utility
with the entire line of input.
The resulting arguments, after replacement is done, will not be allowed to grow
beyond
.Ar replsize
(or 255 if no
.Fl S
flag is specified)
bytes; this is implemented by concatenating as much of the argument
containing
.Ar replstr
as possible, to the constructed arguments to
.Ar utility ,
up to
.Ar replsize
bytes.
The size limit does not apply to arguments to
.Ar utility
which do not contain
.Ar replstr ,
and furthermore, no replacement will be done on
.Ar utility
itself.
Implies
.Fl x .
.It Fl J Ar replstr
If this option is specified,
.Nm
will use the data read from standard input to replace the first occurrence of
.Ar replstr
instead of appending that data after all other arguments.
This option will not affect how many arguments will be read from input
.Pq Fl n ,
or the size of the command(s)
.Nm
will generate
.Pq Fl s .
The option just moves where those arguments will be placed in the command(s)
that are executed.
The
.Ar replstr
must show up as a distinct
.Ar argument
to
.Nm .
It will not be recognized if, for instance, it is in the middle of a
quoted string.
Furthermore, only the first occurrence of the
.Ar replstr
will be replaced.
For example, the following command will copy the list of files and
directories which start with an uppercase letter in the current
directory to
.Pa destdir :
.Pp
.Dl /bin/ls -1d [A-Z]* | xargs -J % cp -Rp % destdir
.It Fl L Ar number
Call
.Ar utility
for every
.Ar number
lines read.
If EOF is reached and fewer lines have been read than
.Ar number
then
.Ar utility
will be called with the available lines.
.It Fl n Ar number , Fl -max-args= Ns Ar number
Set the maximum number of arguments taken from standard input for each
invocation of
.Ar utility .
An invocation of
.Ar utility
will use less than
.Ar number
standard input arguments if the number of bytes accumulated (see the
.Fl s
option) exceeds the specified
.Ar size
or there are fewer than
.Ar number
arguments remaining for the last invocation of
.Ar utility .
The current default value for
.Ar number
is 5000.
.It Fl o
Reopen stdin as
.Pa /dev/tty
in the child process before executing the command.
This is useful if you want
.Nm
to run an interactive application.
.It Fl P Ar maxprocs , Fl -max-procs= Ns Ar maxprocs
Parallel mode: run at most
.Ar maxprocs
invocations of
.Ar utility
at once.
If
.Ar maxprocs
is set to 0,
.Nm
will run as many processes as possible.
.It Fl p , Fl -interactive
Echo each command to be executed and ask the user whether it should be
executed.
An affirmative response,
.Ql y
in the POSIX locale,
causes the command to be executed, any other response causes it to be
skipped.
No commands are executed if the process is not attached to a terminal.
.It Fl r , Fl -no-run-if-empty
Compatibility with GNU
.Nm .
The GNU version of
.Nm
runs the
.Ar utility
argument at least once, even if
.Nm
input is empty, and it supports a
.Fl r
option to inhibit this behavior.
The
.Fx
version of
.Nm
does not run the
.Ar utility
argument on empty input, but it supports the
.Fl r
option for command-line compatibility with GNU
.Nm ,
but the
.Fl r
option does nothing in the
.Fx
version of
.Nm .
.It Fl R Ar replacements
Specify the maximum number of arguments that
.Fl I
will do replacement in.
If
.Ar replacements
is negative, the number of arguments in which to replace is unbounded.
.It Fl S Ar replsize
Specify the amount of space (in bytes) that
.Fl I
can use for replacements.
The default for
.Ar replsize
is 255.
.It Fl s Ar size , Fl -max-chars= Ns Ar size
Set the maximum number of bytes for the command line length provided to
.Ar utility .
The sum of the length of the utility name, the arguments passed to
.Ar utility
(including
.Dv NULL
terminators) and the current environment will be less than or equal to
this number.
The current default value for
.Ar size
is
.Dv ARG_MAX
- 4096.
.It Fl t , Fl -verbose
Echo the command to be executed to standard error immediately before it
is executed.
.It Fl x , Fl -exit
Force
.Nm
to terminate immediately if a command line containing
.Ar number
arguments will not fit in the specified (or default) command line length.
.El
.Pp
If
.Ar utility
is omitted,
.Xr echo 1
is used.
.Pp
Undefined behavior may occur if
.Ar utility
reads from the standard input.
.Pp
If a command line cannot be assembled, or
cannot be invoked, or if an invocation of
.Ar utility
is terminated by a signal,
or an invocation of
.Ar utility
exits with a value of 255, the
.Nm
utility stops processing input and exits after all invocations of
.Ar utility
finish processing.
.Sh EXIT STATUS
The
.Nm
utility exits with a value of 0 if no error occurs.
If
.Ar utility
cannot be found,
.Nm
exits with a value of 127, otherwise if
.Ar utility
cannot be executed,
.Nm
exits with a value of 126.
If any other error occurs,
.Nm
exits with a value of 1.
.Sh EXAMPLES
Create a 3x3 matrix with numbers from 1 to 9.
Every
.Xr echo 1
instance receives three lines as arguments:
.Bd -literal -offset indent
$ seq 1 9 | xargs -L3 echo
1 2 3
4 5 6
7 8 9
.Ed
.Pp
Duplicate every line from standard input:
.Bd -literal -offset indent
$ echo -e "one\\ntwo\\nthree" | xargs -I % echo % %
one one
two two
three three
.Ed
.Pp
Execute at most 2 concurrent instances of
.Xr find 1
every one of them using one of the directories from the standard input:
.Bd -literal -offset indent
echo -e "/usr/ports\\n/etc\\n/usr/local" | xargs -J % -P2 -n1 find % -name file
.Ed
.Sh SEE ALSO
.Xr echo 1 ,
.Xr find 1 ,
.Xr execvp 3
.Sh STANDARDS
The
.Nm
utility is expected to be
.St -p1003.2
compliant.
The
.Fl J , o , P , R
and
.Fl S
options are non-standard
.Fx
extensions which may not be available on other operating systems.
.Sh HISTORY
The
.Nm
utility appeared in PWB UNIX.
.Sh BUGS
If
.Ar utility
attempts to invoke another command such that the number of arguments or the
size of the environment is increased, it risks
.Xr execvp 3
failing with
.Er E2BIG .
.Pp
The
.Nm
utility does not take multibyte characters into account when performing
string comparisons for the
.Fl I
and
.Fl J
options, which may lead to incorrect results in some locales.