grep -sq "" filename && command

grep can be used in combination with && to run a command if a file exists.

This commands lets you generate a random number between the range [$START; $END].

The trick here is to use the brackets [ ] around any one of the characters of the grep string. This uses the fact that [?] is a character class of one letter and will be removed when parsed by the shell. This is useful when you want to parse the output of grep or use the return value in an if-statement without having its own process causing it to erroneously return TRUE.

Using process substitution, we can 'trick' tee into sending a command's STDOUT to an arbitrary number of commands. The last command (command4) in this example will get its input from the pipe.

Files saved on a windows machine use different ascii characters for lines turns. When viewing such files in VI the will most often have a ^M(control-VM) character at the end of each line. This command will remove all occurrences of that character

zsh only

I always hated resorting to using $(seq -w 1 99) to pad numbers. zsh provides a shortcut that couldn't be more intuitive. It also works in reverse {99..01}

zsh only

If you have this command in your history, you can always re-run it and have it reference the latest file.

The glob matches all timestamped files and then the resulting array is sorted by modification time (m) and then the first element in the sorted array is chosen (the latest)

zsh only - This avoids the need for echo "message" | which creates an entire subshell. Also, the text you are most likely to edit is at the very end of the line, which, in my opinion, makes it slightly easier to edit.

The popular fortune program telling by a cow (see sample).

- fortune

- cowsay

Easily list all users

Filter comments and empty lines in files. I find this very useful when trying to find what values are actually set in a very long example config file.

I often set an alias for it, like :

alias nocomment='grep -v "^\($\|#\)"'

!$ recalls the last argument of the previous command. This is very useful when you have to operate several operations on the same file for example.

The $2, $3, $4 fields are arbitrary but note that the first field starts from $2 and the last field is $NF-1. This is due to the fact that the leading and trailing quotes are treated as field delimiters.

KDE4 is great, but still a bit buggy, and sometimes plasma requires to be restarted. Instead of quitting it with "killall plasma", which might loose your preferences (widgets, etc.), kquitapp will cleanly quit it. Tip: you can type this in the "Alt+F2" window, and then type "plasma" in Alt+F2 again to restart plasma (be patient though...).

See which files differ in a diff, and how many changes there are. Very useful when you have tons of differences.

I know its not much but is very useful in time consuming scripts (cron, rc.d, etc).

That "^M" is Ctrl-M, which is a carriage return, and is not needed in Unix file systems.

Where ^V is actually Ctrl-V and ^M is actually Ctrl-M (you must type these yourself, don't just copy and paste this command). ^V will not be displayed on your screen.

only works for freeBSD where ports are installed in /usr/ports

credit to http://wiki.freebsd.org/PortsTasks

The ctrl+v,ctrl+m portion represents key presses that you should do. If you do it successfully you should see a ^M character appear.

deletes first 55 lines; change the 55 to whatever number

changes the PS1 to something better than default.

[username.hostname.last-2-digits-of-ip] (current directory)