3 ms·

One day I have to learn how to use xargs

limaoscarjuliet 9y ago
You and me, both of us. I once combined rpm -e with xargs rpm -ql to the tune of getting all packages uninstalled from the system in one swift command. It was a test system so all good. But I'm still not sure what I was thinking.
pwg 9y ago
The simplest use case for xargs is that you have a list of filenames and you want to feed that list to a command that only accepts filenames as CLI parameters: I.e., 'find' generates a list of filenames. But 'stat' (for example) only accepts file names as parameters on the command line. You combine these two using 'xargs': find -type f -print0 | xargs -0 stat --format="%y\t%n" And you get an output of human readable modification times, a tab, the filename and a newline. Note, the "-print0" to find instructs find to output null terminated filenames, and the -0 to xargs instructs xargs to expect to receive null terminated filenames. These switches (they may be specific to GNU coreutils) allow for handling filenames with any possible character in them correctly (i.e., spaces cause no troubles). For this use case, remembering how/when to use xargs is easy. The more esoteric usages are the ones where "man xargs" is often handy.
cat199 9y ago
It's pretty much 'apply' for shell arguments https://en.wikipedia.org/wiki/Apply https://en.wikipedia.org/wiki/Apply use it many places instead of a for loop: for x in ; do <cmd> $x done is: echo |xargs cmd Assuming 'cmd' can take multiple arguments. If not, use 'xargs -L 1 cmd' to run cmd 1x per arg. GNU xargs has -1, but -L 1 is portable to xargs in the BSDs and others.. plus it's good to know -L in case you ever need to -L 2, etc. using echo as a driver is not the best example, but anyhow.
- cat199 9y ago
  also of note is: -t : print the commands being run -I %: interpolate file name in command string. e.g. ls .mp4 |xargs -t -L 1 -I % scp % me@somebox:/movies to scp individual files (replaced in %) to a destination, one at a time, printing each command as it is run. Again, not the best example since you can scp .mp4 me@sombeox:/movies or rsync, etc. but you get the idea.
  - bitexploder 9y ago
    Find has exec as well. I tend to use this when searching for things.

You and me, both of us. I once combined rpm -e with xargs rpm -ql to the tune of getting all packages uninstalled from the system in one swift command. It was a test system so all good. But I'm still not sure what I was thinking.

pwg 9y ago

The simplest use case for xargs is that you have a list of filenames and you want to feed that list to a command that only accepts filenames as CLI parameters: I.e., 'find' generates a list of filenames. But 'stat' (for example) only accepts file names as parameters on the command line. You combine these two using 'xargs': find -type f -print0 | xargs -0 stat --format="%y\t%n" And you get an output of human readable modification times, a tab, the filename and a newline. Note, the "-print0" to find instructs find to output null terminated filenames, and the -0 to xargs instructs xargs to expect to receive null terminated filenames. These switches (they may be specific to GNU coreutils) allow for handling filenames with any possible character in them correctly (i.e., spaces cause no troubles). For this use case, remembering how/when to use xargs is easy. The more esoteric usages are the ones where "man xargs" is often handy.

cat199 9y ago

It's pretty much 'apply' for shell arguments https://en.wikipedia.org/wiki/Apply https://en.wikipedia.org/wiki/Apply use it many places instead of a for loop: for x in ; do <cmd> $x done is: echo |xargs cmd Assuming 'cmd' can take multiple arguments. If not, use 'xargs -L 1 cmd' to run cmd 1x per arg. GNU xargs has -1, but -L 1 is portable to xargs in the BSDs and others.. plus it's good to know -L in case you ever need to -L 2, etc. using echo as a driver is not the best example, but anyhow.

cat199 9y ago
also of note is: -t : print the commands being run -I %: interpolate file name in command string. e.g. ls .mp4 |xargs -t -L 1 -I % scp % me@somebox:/movies to scp individual files (replaced in %) to a destination, one at a time, printing each command as it is run. Again, not the best example since you can scp .mp4 me@sombeox:/movies or rsync, etc. but you get the idea.
- bitexploder 9y ago
  Find has exec as well. I tend to use this when searching for things.