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restart apache only if config works
making lots of configurations to apache and restarting the server only to find it broken just plain sucks.

Ring the system bell after finishing a long script/compile
This will ring the system bell once if your script exits successfully and twice if it fails. So you can go look at something else and it will alert you when done. Don't forget to use 'xset b [vol [pitch [duration]]]' to get the bell to sound the way you want.

'hpc' in the box - starts a maximum of n compute commands modulo n controlled in parallel
the block of the loop is useful whenever you have huge junks of similar jobs, e.g., convert high res images to thumbnails, and make usage out of all the SMP power on your compute box without flooding the system. note: c is used as counter and the random sleep $ r=`echo $RANDOM%5 |bc`; echo "sleep $r"; sleep $r is just used as a dummy command.

repeat a command every one second
Short method of "while x=0; do foo ; sleep 1 ; done"

Create subdirectory and move files into it
With this form you dont need to cut out target directory using grep/sed/etc.

Convert CSV to JSON
Replace 'csv_file.csv' with your filename.

Generate a ZenCart-style MD5 password hash.
ZenCart uses a MD5 with a salt to secure its passwords. If you need to forcibly change someone's password to a known value within the database, this one-liner can generate the password. Change the value of 'p' to the password you want.

Limit the cpu usage of a process
This will limit the average amount of CPU it consumes.

Change proccess affinity.
Set the affinity of a process to a particular core(s). Arguments for processor include a comma separated list, or a range. (example: 1,2 or 0-3) You can use top in smp mode (Press 1) to see the changes to the affinity.

calculate in commandline with bash
Only works for integer arithmetic.


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