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Random unsigned integer
Reads 4 bytes from the random device and formats them as unsigned integer between 0 and 2^32-1.

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"

Filter IP's in apache access logs based on use
The first sort is necessary for ips in a list to be actually unique.

Search some text from all files inside a directory

Propagate a directory to another and create symlink to content
Lndir create from source directory to destination directory a full symlink tree of all contents of source directory, really useful for propagate changes from a directory to another.

Function to change prompt
Bash function to change your default prompt to something simpler and restore it to normal afterwards.

Reverse SSH
this command from the source server and this follow in the destination server: ssh [email protected] -p 8888

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"

rsync over ssh via non-default ssh port
tested on cygwin and Fedora 9 . good to remember for those jobs where you cannot set a site-specific connect option in your ~/.ssh/config file.

Calculating series with awk: add numbers from 1 to 100
"seq 100" outputs 1,2,..,100, separated by newlines. awk adds them up and displays the sum. "seq 1 2 11" outputs 1,3,..,11. Variations: 1+3+...+(2n-1) = n^2 $ seq 1 2 19 | awk '{sum+=$1} END {print sum}' # displays 100 1/2 + 1/4 + ... = 1 $ seq 10 | awk '{sum+=1/(2**$1)} END {print sum}' # displays 0.999023


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