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

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.\"	@(#)xargs.1	8.1 (Berkeley) 6/6/93
.\" $FreeBSD$
.\"
.Dd May 7, 2001
.Dt XARGS 1
.Os
.Sh NAME
.Nm xargs
.Nd "construct argument list(s) and execute utility"
.Sh SYNOPSIS
.Nm
.Op Fl 0
.Op Fl J Ar replstr
.Oo
.Fl n Ar number
.Op Fl x
.Oc
.Op Fl s Ar size
.Op Fl t
.Op Ar utility Op Ar argument ...
.Sh DESCRIPTION
The
.Nm
utility reads space, tab, newline and end-of-file delimited arguments
from the standard input and executes the specified
.Ar utility
with them as
arguments.
.Pp
The utility and any arguments specified on the command line are given
to the
.Ar utility
upon each invocation, followed by some number of the arguments read
from standard input.
The
.Ar utility
is repeatedly executed 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
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 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 effect 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
.Pp
.It Fl n Ar number
Set the maximum number of arguments taken from standard input for each
invocation of the 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 s 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
Echo the command to be executed to standard error immediately before it
is executed.
.It Fl x
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 no
.Ar utility
is specified,
.Xr echo 1
is used.
.Pp
Undefined behavior may occur if
.Ar utility
reads from the standard input.
.Pp
The
.Nm
utility exits immediately (without processing any further input) if a
command line cannot be assembled,
.Ar utility
cannot be invoked, an invocation of the utility is terminated by a signal
or an invocation of the utility exits with a value of 255.
.Pp
The
.Nm
utility exits with a value of 0 if no error occurs.
If
.Ar utility
cannot be invoked,
.Nm
exits with a value of 127.
If any other error occurs,
.Nm
exits with a value of 1.
.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
option is a non-standard
.Fx
extension which may not be available on other operating systems.
.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 .