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Write comments to your history.
A null operation with the name 'comment', allowing comments to be written to HISTFILE. Prepending '#' to a command will *not* write the command to the history file, although it will be available for the current session, thus '#' is not useful for keeping track of comments past the current session.

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 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" }

One liner to parse all epubs in a directory and use the calibre ebook-convert utility to convert them to mobi format
all ebook-convert -options are optional. all you really need to pass ebook-convert is the incoming and outgoing names, with extensions. Has been tested on Ubuntu 10.10

Display network pc "name" and "workgroup"
Checks for PC samba name and workgroup. Works fine for Windows hosts and Linux/UNIX PCs running Samba.

Copy via tar pipe while preserving file permissions (cp does not!; run this command with root!)
cp options: -p will preserve the file mode, ownership, and timestamps -r will copy files recursively also, if you want to keep symlinks in addition to the above: use the -a/--archive option

Check a server is up. If it isn't mail me.
This version uses netcat to check a particular service.

Advanced python tracing
Trace python statement execution and syscalls invoked during that simultaneously

Finding files with different extensions
This is the way how you can find header and cpp files in the same time.

Non Numeric Check
use to execute a block of code only if $var is numeric


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