Commands using patch (4)

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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.

Determine the version of a specific package with RPM
In this case, I'm getting the package version for 'redhat-release', but of course, this can be applied to any package installed on the filesystem. This is very handy in scripts that need to determine just the version of the package, without the package name and all the sed and grep hackery to get to the data you want. To find out all the support format strings that 'rpm --qf' supports: $ rpm --querytags

camelcase to underscore
Convert a camelCase string into snake_case. To complement senorpedro's command.

kill ip connection
needed; apt-get install tcpkill

Combine all .mpeg files in current directory into one big one.
Good old cat & output redirection. Using this method you can combine all kinds of things - even mpeg files. My video camera makes a series of .mpeg files that are broken into 4gb chunks. Using this command I can easily join them together. Even better, combined with the cp command the files can be copied and joined in one step.

Remove security limitations from PDF documents using ghostscript (for Windows)
#4345 also works under windows

Want to known what time is it in another part of the world ?
available timezone can be found in /usr/share/zoneinfo. Other examples: $ TZ=Europe/Paris date; TZ=Australia/Sydney date; TZ=America/New_York date this is based on zoneinfo files on macosx. Your mileage my vary on other unix dialects

Quickly add user accounts to the system and force a password change on first login
This command is a bit Linux specific, as --stdin doesn't exist for passwd on many Unix machines. Further, useradd is high level in most distributions and Unix derivatives except for the Debian family of distros, where adduser would be more appropriate. The last bit, with chage, will force the user to change their password on new login.

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" }

Display the history and optionally grep
Place this in your .bash_profile and you can use it two different ways. If you issue 'h' on its own, then it acts like the history command. If you issue: $ h cd Then it will display all the history with the word 'cd'

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