Linux – Trying to understand xargs

command linelinuxxargs

The target is not to list temp/run*.* files. The target is to understand why the second command does not work.

First command:

find . \( -name 'temp' \) -print0 | xargs -0 -L 1 -I datafind ls -ltr datafind

list all the files inside temp folders from actual directory

Second command:

find . \( -name 'temp' \) -print0 | xargs -0 -L 1 -I datafind ls -ltr datafind/run*.*

gives cannot access error on every directory that worked with the previous command.

I searched and read man pages and examples but I can not find why the second command does not work. Any clue, please?

Best Answer

The confusion is that wildcard characters such as * and *.* are evaluated by the shell when you type the command.

Therefore datafind/run*.* is evaluated by the shell and would be replaced by the filenames which match that, but it does not find any files that match. Therefore datafind/run*.* is given to the xargs command and then it passes that right through to the ls command.

The ls command does not understand wildcard characters so it just takes its input and tries to find a file with that name. There is no file with the name run*.* so you get an error No such file or directory.

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Command line wizardry: spaces in file names with find | grep | xargs

Are you looking for "howdy doody" in the filename, or within the file?

# find files with "howdy doody" in the filename
find * -name "*howdy doody*" -print0 | xargs -0 ...

xargs is what you need to use to split the null-terminated output from find -print0. In your example, the echo is extraneous; don't bother with it.

# find files containing "howdy doody"
find * -print0 | xargs -0 grep -l "howdy doody"

# find files containing "howdy doody" and do further processing

# multiple xargs version
find * -print0 | xargs -0 grep -l "howdy doody" | xargs -i{} do-something "{}"

# "sh -c" version
find * -print0 | xargs -0 -i{} sh -c 'grep -l "howdy doody" "{}" && do-something "{}"'

# notes: 
#   "sh -c" allows us to run a complex command with a single xargs
#   "{}" handles spaces-in-filename
#   handles any &&, ||, | command linking

You can also run your command directly from the find with -exec. The difference is that find -exec runs the command once per file found; xargs adds filenames to the end of the command (up to system limit), so it runs the command fewer times. You can simulate this with xargs -n1 to force xargs to only run one command per input.

# grep once per file
find * -exec grep -l "howdy doody" {} \; | ...

Linux – How to use find to copy all found files to a new name in their same directories

This solution is probably the most portable:

find "../content" -name "*_compressed.swf" -exec sh -c 'cp {} `dirname {}`/`basename {} compressed.swf`content.swf' \;

There is also the famous rename.pl script which is distributed with Perl, and the rename command which could have made this a bit easier. These aren't available on all distributions though, these commands are for the most part.

Best Answer

Related Solutions

Command line wizardry: spaces in file names with find | grep | xargs

Linux – How to use find to copy all found files to a new name in their same directories

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