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

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Change user within ssh session retaining the current MIT cookie for X-forwarding
When you remotely log in like "ssh -X userA:host" and become a different user with "su UserB", X-forwarding will not work anymore since /home/UserB/.Xauthority does not exist. This will use UserA's information stored in .Xauthority for UserB to enable X-forwarding. Watch http://prefetch.net/blog/index.php/2008/04/05/respect-my-xauthority/ for details.

Analyse an Apache access log for the most common IP addresses
This uses awk to grab the IP address from each request and then sorts and summarises the top 10.

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Check if port is open on remote machine
Check if port is open, if you don't have ncat on your machine.

Execute a command with a timeout
In this example the command "somecommand" will be executed and sent a SIGALARM signal if it runs for more than 10 seconds. It uses the perl alarm function. It's not 100% accurate on timing, but close enough. I found this really useful when executing scripts and commands that I knew might hang E.g. ones that connect to services that might not be running. Importantly this can be used within a sequential script. The command will not release control until either the command completes or the timeout is hit.

translate with google, get all translations
the google-api gives you only one translation which is sometimes insufficent. this function gives you all translations, so you can choose which one fits best.

Extract tarball from internet without local saving

Download all mp3's listed in an html page

Check ps output to see if file is running, if not start it
This comes in handy if you have daemons/programs that have potential issues and stop/disappear, etc., can be run in cron to ensure that a program remains up no matter what. Be advised though, if a program did core out, you'd likely want to know why (gdb) so use with caution on production machines.

Display unique values of a column
the column number is '6'


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