While copying a large file that may take up a good chunk of your hard drive, start the copy and run this command concurrently. It will print out the disk information every second. It's pretty handy when you have a large copy with nothing to monitor the progress.

This will convert filenames from uppercase to lowercase. I find this useful after downloading images from my digital camera. This works for English, but other languages may need something slightly more complex like this:

Also, the quote marks aren't necessary if your filenames don't contain spaces.

Windows

I have this on a daily cronjob to backup the commandlinefu.com database from NearlyFreeSpeech.net (awesome hosts by the way) to my local drive. Note that (on my Ubuntu system at least) you need to escape the % signs on the crontab.

My variant on this common function. Some highlights:

Allows you to override the default ps args of "aux"

Uses bracket trick to omit the grep process itself without having to use a second grep

Always prints the correct header row of ps output

Limitations: Ugly ps error output if you forget to quote your multi word grep argument

It is a pain grep-ing/sed-ing/awk-ing plain old df. POSIX it!

The expansion {,} in bash will repeat the given string once for each item seperated by commas. The given command will result in the following being run:

cp /really/long/path/and/file/name /really/long/path/and/file/name-`date -I`

These can be embedded as needed, ex: rm file{1,2,3{1,2,3}} would delete the files file1, file2, file31, file32, file32, and no other files.

Countdown from 10 or whatever you want:)

trap is the bash builtin that allows you to execute commands when the current script receives a particular signal.

Uses $0 for the script name, $$ for the script PID, tee to output to STDOUT as well as a log file and ps to log other running processes.

available timezone can be found in /usr/share/zoneinfo. Other examples:

this is based on zoneinfo files on macosx. Your mileage my vary on other unix dialects

You can exclude more system folders or individual files which are not necessary for the backup and can be recreated after the restore procedure, like /lost+found, /mnt, /media, /tmp, /usr ...

Restoring the above backup procedure is as simple as becoming root and typing:

You can extract any file or directory out of the backup.tgz file for recovery, for instance, if you have a corrupt or mis-configured fstab file, you could simply issue the command:

Other options:

v add verbose option to see files processed

A far safer solution is to restore the desired files under a different directory, and then compare, move, or update the files to their original locations afterward.

Using the redundant ./ directory information prevents the dash from occurring at the beginning of the filename, and being interpreted as an option of the rm command.

Also works using:

This will print to the screen password for the user specified in "sys_users.login='xxxx';. This is for Plesk servers only.

Alrighty, so I was really bored ;)

Lifted from http://linux.spiney.org/remote_diff_with_vim_and_ssh which points out credits for the inspiration.

unsets variables used by the one-liner

sets up the IFS bash variable to not be affected by whitespace and disables extra glob expansion

uses read to slurp the results of the find command into an array

selects an element of the array at random to be passed as an argument to mplayer

This command takes the output of the 'last' command, removes empty lines, gets just the first field ($USERNAME), sort the $USERNAMES in reverse order and then gives a summary count of unique matches.

Insert a comma where necessary when counting large numbers. I needed to separate huge amounts of packets and after 12+ hours of looking in a terminal, I wanted it in readable form.

(WARN) This will absolutely not work on all systems, unless you're running large, high speed, hardware RAID arrays. For example, systems using Dell PERC 5/i SAS/SATA arrays. If you have a hardware RAID array, try it. It certainly wont hurt.

You may be can test the speed disk with some large file in your system, before and after using this:

To know the value of block device parameter known as readahead.

And set the a value 1024, 2048, 4096, 8192, and maybe 16384... it really depends on the number of hard disks, their speed, your RAID controller, etc. (see sample)

Sometimes, in a shell script, you need a random number bigger than the range of $RANDOM. This will print a random number made of four hex values extracted from /dev/urandom.

I put this in a shell script called "svndiff", as it provides a handy decorated "svn diff" output that is colored (which you can't see here) and paged. The -r is required so less doesn't mangle the color codes.