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Show max lengths of all fields in a pipe delimited file with header row

Find directories under home directory with 777 permissions, change to 755, and list them on console

bash test check validate if variable is number
to test check if given variable is a digit / number

Remove all unused kernels with apt-get
This should do the same thing and is about 70 chars shorter.

Pick a random line from a file
This is from perldoc -q random.*line, which says: This has a significant advantage in space over reading the whole file in. You can find a proof of this method in The Art of Computer Programming, Volume 2, Section 3.4.2, by Donald E. Knuth. Who am I to argue with Don Knuth?

Periodically run a command without hangups, and send the output to your e-mail
Run "ps -x" (process status) in the background every hour (in this example). The outputs of both "nohup" and "ps -x" are sent to the e-mail (instead of nohup.out and stdout and stderr). If you like it, replace "ps -x" by the command of your choice, replace 3600 (1 hour) by the period of your choice. You can run the command in the loop any time by killing the sleep process. For example $ ps -x 2925 ? S 0:00.00 sh -c unzip E.zip >/dev/null 2>&1 11288 ? O 0:00.00 unzip E.zip 25428 ? I 0:00.00 sleep 3600 14346 pts/42- I 0:00.01 bash -c while true; do ps -x | mail pascalv; sleep 3600; done 643 pts/66 Ss 0:00.03 -bash 14124 pts/66 O+ 0:00.00 ps -x $ kill 25428 You have mail in /mail/pascalv

Remove security limitations from PDF documents using ghostscript (for Windows)
#4345 also works under windows

Press ctrl+r in a bash shell and type a few letters of a previous command
In the sample output, I pressed ctrl+r and typed the letters las. I can't imagine how much typing this has saved me.

sqlite3 cmd to extract Firefox bookmarks from places.sqlite
Found this useful query at http://id.motd.org/pivot/entry.php?id=22. The b.parent=2 in the command refers to the bookmarks folder to extract. See the source webpage for additional info.

Convert JSON to YAML
Convert JSON to YAML. Note that you'll need to have PyYaml installed.


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