xargs - Constructs argument lists and runs commands
xargs [-e[eofstr]] [-E eofstr] [-i[replstr]] [-I replstr]
[-l[number]] [-L number] [-n[number]] [-ptrx] [-slength]
[CommandString] [argument...]
The xargs command constructs a command line by combining a
command string, containing a command and its options or
arguments, with additional arguments read from standard
input.
Interfaces documented on this reference page conform to
industry standards as follows:
xargs: XCU5.0
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Sets the logical end-of-file string to eofstr. The xargs
command reads standard input until it encounters either an
end-of-file character or the logical end-of-file string.
If you do (underline). If you specify -e with no eofstr,
xargs interprets the underline character as a literal
character, rather than as an end-of-file marker. Specifies
a logical end-of-file string to replace the default
underscore. The xargs command reads standard input until
either an end-of-file character or the logical end-of-file
string is encountered. Takes an entire line as a single
argument and inserts it in each instance of replstr found
in the command string. A maximum of five arguments in the
command string can each contain one or more instances of
replstr. The xargs command discards spaces and tabs at
the beginning of each line. The argument constructed cannot
be larger than 255 bytes. The default replstr is {}.
This option also turns on the -x option. Insert mode:
command is executed for each line from standard input,
taking the entire line as a single argument, inserting it
in arguments for each occurrence of replstr. Any blank
characters at the beginning of each line are ignored. Constructed
arguments cannot grow larger than 255 bytes.
Option -x is forced on. The -I and -i options are mutually
exclusive; the last one specified takes effect. Runs the
command string with the specified number of nonempty argument
lines read from standard input. The last invocation
of the command string can have fewer argument lines if
fewer than number remain. A line ends with the first newline
character unless the last character of the line is a
space or a tab. A trailing space or tab indicates a continuation
through the next nonempty line. The default number
is 1. This option turns on the -x option. The command
is executed for each non-empty number lines of argument
from standard input. The last invocation of command
has fewer lines of argument if fewer than number remain. A
line is considered to end with the first newline character
unless the last character of the line is a blank character.
A trailing blank character signals continuation to
the next non-empty line, inclusive. The -L, -l and -n
options are mutually exclusive; the last one takes effect.
Executes the command string using as many standard input
arguments as possible, up to a maximum of number. The
xargs command uses fewer arguments if their total length
is greater than the number of characters specified by the
-s [length] option. It also uses fewer arguments for the
last invocation if fewer than number arguments remain.
When -x is present, each number argument must fit the
length limitation specified by -s. Asks whether or not to
run the command string. It displays the constructed command
line, followed by a ?... prompt. Press y, or the
locale's equivalent of a y, to run the command string.
Any other response causes xargs to skip that particular
invocation of the command string. You are asked about
each invocation. Sets the maximum total length of each
argument list. The length must be a positive integer less
than or equal to 470. The default length is 470 bytes.
Note that the character count for length includes one
extra character for each argument and the number of characters
in the command name. Echoes the command string and
each constructed argument list to file descriptor 2 (usually
standard error). Stops running xargs if any argument
list is greater than the number of characters specified by
the -s length option. This option is turned on if you
specify either the -i or -l options. If you do not specify
-i, -l, or -n, the total length of all arguments must
be within the length limit.
The name of the command to be invoked, found by searching
the path using the PATH environment variable. If CommandString
is omitted, the default is the echo command. An
initial option or operand for the invocation of CommandString.
The xargs command runs the command string as many times as
necessary to process all input arguments. The default
command string is echo.
Arguments read from standard input are character strings
delimited by one or more spaces, tabs, or newline characters.
You can embed a space or a tab in arguments by preceding
it with a \ (backslash) or by quoting it. The
xargs command reads characters enclosed in single or double
quotes as literals and removes the delimiting quotes.
It always discards empty lines.
The xargs command ends if it cannot run the command string
or if it receives an exit code of -1. When the command
string calls a shell procedure, the shell procedure should
explicitly exit with an appropriate value to avoid accidentally
returning -1. (See the sh command.)
The LC_MESSAGES variables determines the locale's equivalent
of y and n (for yes/no queries).
The following exit values are returned: All invocations of
CommandString returned exit status zero. A command line
meeting the specified requirements could not be assembled,
one or more of the invocations of CommandString returned a
non-zero exit status, or some other error occurred. The
command specified by CommandString was found but could not
be invoked. The command specified by CommandString could
not be found.
To use a command on files whose names are listed in a
file, use a command line similar to the following: xargs
lint -a < cfiles
If cfiles contains the text, enter: main.c readit.c
gettoken.c putobj.c
then xargs constructs and runs the command: lint
-a main.c readit.c gettoken.c putobj.c
Each shell command line can be up to 470 bytes
long. If cfiles contains more file namess than fit
on a single line, then xargs runs the lint command
with the file namess that fit. It then constructs
and runs another lint command using the remaining
file namess. Depending on the names listed in
cfiles, the commands might look like the following:
lint -a main.c readit.c gettoken.c... lint -a
getisx.c getprp.c getpid.c... lint -a fltadd.c
fltmult.c fltdiv.c...
This is not quite the same as running lint once
with all the file namess. The lint command checks
cross-references between files. However, in this
example it cannot check between main.c and
fltadd.c, or between any two files listed on separate
command lines.
For this reason you might want to run the command
only if all the file namess fit on one line. Do
this by using xargs with the -x option: xargs -x
lint -a <cfiles
If all the file names in cfiles do not fit on one
command line, then xargs displays an error message.
To construct commands that contain a certain number
of file namess, use a command line similar to the
following: xargs -t -n2 diff <<end starting
chap1 concepts chap2 writing chap3 end
This constructs and runs diff commands that contain
two file names each (-n2):
diff starting chap1 diff concepts chap2 diff
writing chap3
The -t option tells xargs to display each command
before running it so that you can see what is happening.
The <<end and end arguments define a Here
Document, which uses the text entered before the
end line as standard input for the xargs command.
(For more details, see the section Inline Input
(Here) Documents in the sh(1) reference page.) To
insert file namess into the middle of commands, use
a command line similar to the following: ls |
xargs -t -i mv {} {}.old
This renames all files in the current directory by
adding to the end of each name. The -i tells xargs
to insert each line of the ls directory listing
where { } (braces) appear. If the current directory
contains the files chap1, chap2, and chap3,
then this constructs the following commands:
mv chap1 chap1.old mv chap2 chap2.old mv chap3
chap3.old To run a command on files that you select
individually, use a command line similar to the
following: ls | xargs -p -n1 ar r lib.a
This allows you to select files to add to the
library lib.a. The -p option tells xargs to display
each ar command it constructs and ask if you
want to run it. Press y, or the locale's equivalent
of a y, and press <Return> to run the command.
Press <Return> alone if you do not want to run it.
ENVIRONMENT VARIABLES [Toc] [Back] The following environment variables affect the execution
of xargs: Provides a default value for the internationalization
variables that are unset or null. If LANG is unset
or null, the corresponding value from the default locale
is used. If any of the internationalization variables
contain an invalid setting, the utility behaves as if none
of the variables had been defined. If set to a non-empty
string value, overrides the values of all the other internationalization
variables. Determines the locale for the
interpretation of sequences of bytes of text data as characters
(for example, single-byte as opposed to multibyte
characters in arguments and input files) and the behavior
of character classes used for yesexprlocal keyword in the
LC_MESSAGES category. Determines the locale for the format
and contents of diagnostic messages written to standard
error. Determines the location of message catalogues
for the processing of LC_MESSAGES. Determines the location
of CommandString.
Commands: ksh(1), Bourne shell sh(1b), POSIX shell sh(1p)
Standards: standards(5)
xargs(1)
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