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Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.
Use your favourite RSS aggregator to stay in touch with the latest commands. There are feeds mirroring the 3 Twitter streams as well as for virtually every other subset (users, tags, functions,…):
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The popular fortune program telling by a cow (see sample).
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)
gpg command to encrypt a file on the command line.
gpg command to decrypt a previously encrypted file on the command line.
Can be optionally made into an alias:
alias decrypt='gpg --output foo.txt --decrypt foo.txt.pgp'
For quick validation of folder's file-contents (structure not taken into account) - I use it mostly to check if two folders' contents are the same.
-p PID and name of the program
-u on a UDP port.
-t also TCP ports
-o networking timer
-n numeric IP addresses (don't resolve them)
-a all sockets
show phpinfo(); from the command line
This command converts a MySQL query directly into a .csv (Comma Seperated Value)-file.
You can read, add, delete and modify Windows permissions from Linux using smbcacls from the smb-client package.
Very useful set of commands to know when your file system was created.