xargs¶
Introduction¶
This page contains a few examples of the xargs command that I want to keep at hand. I’m not very familiar with xargs and often resort to a “cheatsheet” (e.g. Mastering Xargs: Your Guide to Linux Command Efficiency) when I have to use it.
Splitting null terminated input items¶
Sometimes you need to list the environement variables of a running Linux
process. If you just do cat /proc/<PID>/environ, you get a single long line
of output with all the environement variables of the process with PID <PID>.
This is because the environement variables are separated by the null character.
There are at least two solutions based on xargs to get the environement variables on separate lines:
cat /proc/<PID>/environ | xargs -0 printf '%s\n'
cat /proc/<PID>/environ | xargs -0 -L1
You can avoid the pipe with the -a option which instructs xargs to read
items from the specified file instead of standard input:
xargs -0 -L1 -a /proc/<PID>/environ
All this also works for /proc/<PID>/cmdline (command line arguments of a
process). If you want the arguments separated by blanks on a single line do:
xargs -0 -a /proc/<PID>/cmdline
Executing a command for each item¶
A command like:
any_command | xargs -n 1 other_command
causes other_command to be executed once for each item output by
any_command.
Executing a command for each item (with item used anywhere in the command)¶
This makes use of the -I option of xargs. The “{}” following -I means
that later occurrences of “{}” are substituted with the item.
Here is an example involving the cleartool command (primary command-line
interface to ClearCase
version-control and configuration management software):
cleartool lsco -all -me -short -cview \
| xargs -I {} sh -c \
'diff --unified $(cleartool describe -fmt '%En@@%PVn\\\\n' {}) {}'
