NAME

xe — execute a command for every argument

SYNOPSIS

DESCRIPTION

The xe utility constructs command lines from specified arguments, combining some of the best features of xargs(1) and apply(1).

xe means “execute for every ...”.

xe supports different methods to specify arguments to commands:

command ...

By default, arguments - separated by newlines - are read from the standard input. The resulting command is constructed from the command line parameters, replacing replace-arg with the read argument, and is executed with execvp(3).

In this mode, no shell is involved and replace-arg must appear as a word on its own, i.e. ‘foo {} bar’ will work, but ‘foo{} bar’ will not, where {} is the default value for replace-arg.

If no argument is specified, the default is ‘printf %s\n’.

-f argfile

Read arguments from argfile, instead of the standard input.

This does not close the standard input for execution, it is passed to the forked process.

-s shellscript

In this mode, the single parameter shellscript is executed using sh -c. In the script, the specified arguments can be accessed using $1, $2, ...

For example:

echo 'a\nb' | xe -N2 -s 'echo $2 $1'

-a command ... -- args ...

In this mode, everything after -- is passed as args to command.

-A argsep command ... argsep args ...

Same as -a, but the custom argument separator argsep is used to distinguish between command and its args.

The options are as follows:

-0

Input filenames are separated by NUL bytes (instead of newlines, which is the default)

-F

Fatal: stop and exit when a command execution fails.

-L

Run the resulting commands with line-buffered output; lines from two jobs will not interleave. When used twice, or with -vv, also prefix each line with the number of the job (see ENVIRONMENT) in such a manner that the output can be piped to ‘sort -snk1’ to group it.

-R

Return with status 122 when no arguments have been specified (instead of 0, the default). xe never executes a command when no arguments are specified.

-n

Dry run: don't run the resulting commands, just print them.

-q

Quiet mode: redirect standard output and standard error of commands to /dev/null.

-v

Verbose: print commands to standard error before running them. When used twice, also print job id and exit status for each command.

-p

Enable make(1)-style percent rules. The first argument of command ... is regarded as a pattern, see PERCENT RULES below. Patterns without a slash (or ‘**’) are matched against the basenames only.

Multiple runs of patterns and commands are separated by ‘+’. Only the first matching percent rule is executed; in case no pattern matches, no command is run.

-I replace-arg

Replace first occurrence of replace-arg (default: {}) in the resulting command with the argument(s). Pass an empty replace-arg to disable the replace function. Contrary to xargs(1) this will expand into multiple arguments when needed.

-N maxargs

Pass up to maxargs arguments to each command (default: 1).
Using -N0 will pass as many arguments as possible.

-j maxjobs

Run up to maxjobs processes concurrently. Using -j0 will run as many processes as there are CPU cores running. If maxjobs ends with an ‘x’, it is regarded as a multiplier of the number of running CPU cores (rounded down, but using at least one core).

PERCENT RULES

The percent rules of xe are similar to the globs of sh(1) or fnmatch(3): ‘?’ matches a single character that is not ‘/’. ‘/’ matches one or multiple ‘/’ in the string. ‘*’ matches zero or more characters, but never ‘/’. ‘**’ matches zero or more characters, including ‘/’. Note that all of these also match leading dots in file names.

‘{a,b,c}’ matches either a, b or c. ‘[abc]’ matches one of the characters abc (but never ‘/’). ‘[!abc]’ matches all characters but abc. Alternatively, ‘[^abc]’ can be used too. ‘[a-c]’ matches any character in the range between a and c inclusive. In character ranges, characters can be escaped using a backslash.

In the pattern, a single occurrence of ‘%’ matches one or more characters, and replaces the first occurrence of ‘%’ with the matched string in the remaining arguments, which are then used as the command to be executed.

ENVIRONMENT

The environment variable ITER is passed to the child process and incremented on each command execution.

EXIT STATUS

xe follows the convention of GNU and OpenBSD xargs:

0

on success

123

if any invocation of the command exited with status 1 to 125.

124

if the command exited with status 255

125

if the command was killed by a signal

126

if the command cannot be run

127

if the command was not found

1

if some other error occurred

Additionally, 122 is returned when -R was passed and the command was never executed.

EXAMPLES

Compress all .c files in the current directory, using all CPU cores:

SEE ALSO

apply(1), parallel(1), xapply(1), xargs(1)

AUTHORS

Leah Neukirchen <leah@vuxu.org>

LICENSE

xe is in the public domain.

To the extent possible under law, the creator of this work has waived all copyright and related or neighboring rights to this work.

http://creativecommons.org/publicdomain/zero/1.0/