Content-type: text/html Man page of xargs

xargs

Section: User Commands (1)
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NAME

xargs - Constructs argument lists and runs commands  

SYNOPSIS

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.
 

STANDARDS

Interfaces documented on this reference page conform to industry standards as follows:

xargs:  XPG4, XPG4-UNIX

Refer to the standards(5) reference page for more information about industry standards and associated tags.
 

OPTIONS

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.
 

OPERANDS

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.
 

DESCRIPTION

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).
 

EXIT STATUS

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.
 

EXAMPLES

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 .old 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

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.
 

SEE ALSO

Commands:  ksh(1), Bourne shell sh(1b), POSIX shell sh(1p)

Standards:  standards(5)


 

Index

NAME
SYNOPSIS
STANDARDS
OPTIONS
OPERANDS
DESCRIPTION
EXIT STATUS
EXAMPLES
ENVIRONMENT VARIABLES
SEE ALSO

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Time: 02:42:45 GMT, October 02, 2010