Hide

What's this?

commandlinefu.com is the place to record those command-line gems that you return to again and again.

Delete that bloated snippets file you've been using and share your personal repository with the world. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.


If you have a new feature suggestion or find a bug, please get in touch via http://commandlinefu.uservoice.com/

Get involved!

You can sign-in using OpenID credentials, or register a traditional username and password.

First-time OpenID users will be automatically assigned a username which can be changed after signing in.

Hide

Stay in the loop…

Follow the Tweets.

Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.

» http://twitter.com/commandlinefu
» http://twitter.com/commandlinefu3
» http://twitter.com/commandlinefu10

Subscribe to the feeds.

Use your favourite RSS aggregator to stay in touch with the latest commands. There are feeds mirroring the 3 Twitter streams as well as for virtually every other subset (users, tags, functions,…):

Subscribe to the feed for:

Hide

News

2011-03-12 - Confoo 2011 presentation
Slides are available from the commandlinefu presentation at Confoo 2011: http://presentations.codeinthehole.com/confoo2011/
2011-01-04 - Moderation now required for new commands
To try and put and end to the spamming, new commands require moderation before they will appear on the site.
2010-12-27 - Apologies for not banning the trolls sooner
Have been away from the interwebs over Christmas. Will be more vigilant henceforth.
2010-09-24 - OAuth and pagination problems fixed
Apologies for the delay in getting Twitter's OAuth supported. Annoying pagination gremlin also fixed.
Hide

Tags

Hide

Functions

Commands tagged job control from sorted by
Terminal - Commands tagged job control - 13 results
^Z <...> % &
2014-06-13 15:35:52
User: Dev_NIX
Tags: job control
0

Like this you can continue a suspended job without blocking again your terminal

for host in $HOSTNAMES; do ping -q -c3 $host && ssh $host 'command' & for count in {1..15}; do sleep 1; jobs | wc -l | grep -q ^0\$ && continue; done; kill %1; done &>/dev/null
for host in $MYHOSTS; do ping -q -c3 $H 2>&1 1>/dev/null && ssh -o 'AllowedAuthe ntications publickey' $host 'command1; command2' & for count in 1 2 3 4 5; do sleep 1; jobs | wc -l | grep -q ^0\$ && continue; done; kill %1; done
2012-11-13 23:12:27
User: a8ksh4
Functions: grep host jobs kill ping sleep ssh wc
0

Execute commands serially on a list of hosts. Each ssh connection is made in the background so that if, after five seconds, it hasn't closed, it will be killed and the script will go on to the next system.

Maybe there's an easier way to set a timeout in the ssh options...

jobs | grep -o "[0-9]" | while read j; do kill %$j; done
2012-04-12 17:29:58
User: haggen
Functions: grep jobs kill read
0

List background jobs, grep their number - not process id - and then kill them

^z; bg; disown
2011-12-06 20:48:01
User: anarcat
3

background and disown, but with a proper one-line syntax

^Z <...> %
2011-11-20 00:12:47
User: lordtoran
Tags: job control
5

Press ^Z, do what you need to do on the shell, then input % to resurrect the suspended job.

command & echo $!
2011-06-08 18:16:38
User: Mahrud
Functions: command echo
-2

Actually $! is an internal variable containing PID of the last job in background.

More info: http://tldp.org/LDP/abs/html/internalvariables.html#PIDVARREF

Using $! for job control:

possibly_hanging_job & { sleep ${TIMEOUT}; eval 'kill -9 $!' &> /dev/null; }
sleeper(){ while `ps -p $1 &>/dev/null`; do echo -n "${2:-.}"; sleep ${3:-1}; done; }; export -f sleeper
12

Very useful in shell scripts because you can run a task nicely in the background using job-control and output progress until it completes.

Here's an example of how I use it in backup scripts to run gpg in the background to encrypt an archive file (which I create in this same way). $! is the process ID of the last run command, which is saved here as the variable PI, then sleeper is called with the process id of the gpg task (PI), and sleeper is also specified to output : instead of the default . every 3 seconds instead of the default 1. So a shorter version would be sleeper $!;

The wait is also used here, though it may not be needed on your system.

echo ">>> ENCRYPTING SQL BACKUP" gpg --output archive.tgz.asc --encrypt archive.tgz 1>/dev/null & PI=$!; sleeper $PI ":" 3; wait $PI && rm archive.tgz &>/dev/null

Previously to get around the $! not always being available, I would instead check for the existance of the process ID by checking if the directory /proc/$PID existed, but not everyone uses proc anymore. That version is currently the one at http://www.askapache.com/linux-unix/bash_profile-functions-advanced-shell.html but I plan on upgrading to this new version soon.

S=$SSH_TTY && (sleep 3 && echo -n 'Peace... '>$S & ) && (sleep 5 && echo -n 'Love... '>$S & ) && (sleep 7 && echo 'and Intergalactic Happiness!'>$S & )
2009-08-19 07:57:16
User: AskApache
Functions: echo sleep
-2

Ummmm.. Saw that gem on some dead-head hippies VW bus at phish this summer.. It's actually one of my favorite ways of using bash, very clean. It shows what you can do with the cool advanced features like job control, redirection, combining commands that don't wait for each other, and the thing I like the most is the use of the ( ) to make this process heirarchy below, which comes in very handy when using fifos for adding optimization to your scripts or commands with similar acrobatics.

F UID PID PPID WCHAN RSS PSR CMD

1 gplovr 30667 1 wait 1324 1 -bash

0 gplovr 30672 30667 - 516 3 \_ sleep 3

1 gplovr 30669 1 wait 1324 1 -bash

0 gplovr 30673 30669 - 516 0 \_ sleep 5

1 gplovr 30671 1 wait 1324 1 -bash

0 gplovr 30674 30671 - 516 1 \_ sleep 7

nohup /bin/sh myscript.sh 1>&2 &>/dev/null 1>&2 &>/dev/null&
2009-08-18 07:24:52
User: AskApache
Functions: nohup
6

This command runs your shell script in the background with no output of any kind, and it will remain running even after you logout.

chronic () { t=$1; shift; while true; do $@; sleep $t; done & }
2009-06-13 05:57:54
User: rhythmx
Functions: sleep
3

Chronic Bash function:

chronic 3600 time # Print the time in your shell every hour chronic 60 updatedb > /dev/null # update slocate every minute

Note: use 'jobs' to list background tasks and fg/bg to take control of them.

^Z $bg $disown
2009-03-17 21:52:52
User: fall0ut
47

You're running a script, command, whatever.. You don't expect it to take long, now 5pm has rolled around and you're ready to go home... Wait, it's still running... You forgot to nohup it before running it... Suspend it, send it to the background, then disown it... The ouput wont go anywhere, but at least the command will still run...

^Z then bg