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Remove comments from files
Use sed to remove comments from a file. In this example the comments begin with #. The command '/^#/d' remove line starting with #. The command 's/#.*$//' remove comments at end of lines.

Empty a file
For when you want to flush all content from a file without removing it (hat-tip to Marc Kilgus).

Recall “N”th command from your BASH history without executing it.

Get your external IP address ( 10 characters long )
Shortest url to a external IP-service, 10 characters.

Check if a domain is available and get the answer in just one line
Returns nothing if the domain exists and 'No match for domain.com' otherwise.

If (and only if) the variable is not set, prompt users and give them a default option already filled in.
The read command reads input and puts it into a variable. With -i you set an initial value. In this case I used a known environment variable.

Create a backup of the file.
It will create a backup of the filename. The advantage is that if you list the folder the backups will be sorted by date. The command works on any unix in bash.

find system's indianness

Open Remote Desktop (RDP) from command line having a custom screen size
This example uses xfreerdp, which builds upon the development of rdesktop. This example usage will also send you the remote machine's sound.

Convert seconds to [DD:][HH:]MM:SS
Converts any number of seconds into days, hours, minutes and seconds. sec2dhms() { declare -i SS="$1" D=$(( SS / 86400 )) H=$(( SS % 86400 / 3600 )) M=$(( SS % 3600 / 60 )) S=$(( SS % 60 )) [ "$D" -gt 0 ] && echo -n "${D}:" [ "$H" -gt 0 ] && printf "%02g:" "$H" printf "%02g:%02g\n" "$M" "$S" }


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