Commands using egrep (220)

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Get the size of all the directories in current directory (Sorted Human Readable)
as per eightmillion's comment. Simply economical :)

count the number of specific characters in a file or text stream
In this example, the command will recursively find files (-type f) under /some/path, where the path ends in .mp3, case insensitive (-iregex). It will then output a single line of output (-print0), with results terminated by a the null character (octal 000). Suitable for piping to xargs -0. This type of output avoids issues with garbage in paths, like unclosed quotes. The tr command then strips away everything but the null chars, finally piping to wc -c, to get a character count. I have found this very useful, to verify one is getting the right number of before you actually process the results through xargs or similar. Yes, one can issue the find without the -print0 and use wc -l, however if you want to be 1000% sure your find command is giving you the expected number of results, this is a simple way to check. The approach can be made in to a function and then included in .bashrc or similar. e.g. $ count_chars() { tr -d -c "$1" | wc -c; } In this form it provides a versatile character counter of text streams :)

Command to rename multiple file in one go

Resolve a list of domain names to IP addresses
Given a file of FQDN, this simple command resolves the IP addresses of those Useful for log files or anything else that outputs domain names.

a find and replace within text-based files, for batch text replacement, not using perl
Use sed to edit in-place a list of files returned by find.

display a smiling smiley if the command succeeded and a sad smiley if the command failed
you could save the code between if and fi to a shell script named smiley.sh with the first argument as and then do a smiley.sh to see if the command succeeded. a bit needless but who cares ;)

Compress a series of png pictures to an avi movie.
cd /path/to/your/png_pics mencoder "mf://*.png" -mf fps=2 -o output.avi -ovc lavc -lavcopts vcodec=mpeg4 then you can get a movie named output.avi.

search for a file in PATH

Brute force discover
Show the number of failed tries of login per account. If the user does not exist it is marked with *.

Clone or rescue a block device
If you use the logfile feature of ddrescue, the data is rescued very efficiently (only the needed blocks are read). Also you can interrupt the rescue at any time and resume it later at the same point. http://www.gnu.org/software/ddrescue/ddrescue.html


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