XE(1)

NAME
xe - execute a command for every argument

SYNOPSIS
xe [-0FLRnqv] [-I replace-arg] [-N maxargs] [-j maxjobs] command ...
xe [flags ...] -p pattern command ... [+ pattern command ...]...
xe [flags ...] -f argfile command ...
xe [flags ...] -s shellscript
xe [flags ...] -a command ... -- args ...
xe [flags ...] -A argsep command ... argsep args ...

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:
    xe -a -j0 gzip -- *.c
Remove all empty files, using lr(1):
    lr -U -t 'size == 0' | xe -N0 rm
Convert .mp3 to .ogg, using all CPU cores:
    xe -a -j0 -s 'ffmpeg -i "${1}" "${1%.mp3}.ogg"' -- *.mp3
Same, using percent rules:
    xe -a -j0 -p %.mp3 ffmpeg -i %.mp3 %.ogg -- *.mp3
Similar, but hiding output of ffmpeg, instead showing spawned jobs:
    xe -ap -j0 -vvq '%.{m4a,ogg,opus}' ffmpeg -y -i {} out/%.mp3 -- *

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/