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Quick calculator at the terminal
Useful for quick calculations at the command line. $math_expr is any arithmetic expression (see sample output): 4.5*16+3^2 s(3.1415926/2) More options in the bc man page.

Find broken symlinks

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"

convert mp3 into mb4 (audiobook format)
to convert a whole directory, put all mp3 files in a for loop $ for i in $(ls *mp3); do mpg123 -s $i | faac -b 80 -P -X -w -o ${i%mp3}m4b -; done

Create a mirror of a local folder, on a remote server
Create a exact mirror of the local folder "/root/files", on remote server 'remote_server' using SSH command (listening on port 22) (all files & folders on destination server/folder will be deleted)

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"

awk using multiple field separators
You can use multiple field separators by separating them with | (=or). This may be helpful when you want to split a string by two separators for example. #echo "one=two three" | awk -F "=| " {'print $1, $3'} one three

watch iptables counters
This will allow you to watch as matches occur in real-time. To filter out only ACCEPT, DROP, LOG..etc, then run the following command: watch 'iptables -nvL | grep -v "0 0" && grep "ACCEPT"' The -v is used to do an inverted filter. ie. NOT "0 0"

grep processes list avoiding the grep itself
Trick to avoid the form: grep process | grep - v grep

split a multi-page PDF into separate files
Have to do this once per output file, because if device is 'pdfwrite', even if 'gs' sees '%d' in the OutputFile it still only creates one single output file. Embed it into a simple shell script if you want to split a document out into one file for every page.


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