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Prevent overwriting file when using redirection
If you set noclobber to on, bash won't allow redirection to overwrite existing files . $ set -o noclobber command turn the option on (default it s off ) . You can still append information but not overwrite the file .to turn it back off use : $ set +o noclobber . I use it because i overwrite a file by accident , after thought , content of the file was very important , creating a one more file mean nothing for my hard disk (we are not anymore on the 64 k memory time) , but content of file is far much important . What we call exeprience :(

List 10 largest directories in current directory
du -m option to not go across mounts (you usually want to run that command to find what to destroy in that partition) -a option to also list . files -k to display in kilobytes sort -n to sort in numerical order, biggest files last tail -10 to only display biggest 10

Summarize the number of open TCP connections by state
Useful for checking the number and state of TCP connections.

check site ssl certificate dates
remotely connects to an https site, fetches the ssl certificate and displays the valid dates for the cert

Increase mplayer maximum volume
use '0' and '9' to increase/decrease volume. this is useful on laptops with low speaker volume.

convert a web page into a png
This requires the command-line print extension (see #2861 for more details). I use it to make up complex images with formatted text using CSS and whatnot. It's a lot slicker than imagemagick for certain things. Now imagine using a local webserver with PHP and a database to generate the images. Oh, the possibilities...

put an unpacked .deb package back together
If any changes have been made to the package while it was unpacked (ie, conffiles files in /etc modi‐fied), the new package will inherit the changes. This way you can make it easy to copy packages from one computer to another, or to recreate packages that are installed on your system, but no longer available elsewhere. Note: dpkg-repack will place the created package in the current directory.

prevent accidents while using wildcards
alternative for "echo rm *.txt". Just doubletab the command you are willing to use and it will show you the affected files.

convert single digit to double digits
Uses 'rename' to pad zeros in front of first existing number in each filename. The "--" is not required, but it will prevent errors on filenames which start with "-". You can change the "2d" to any number you want, equaling the total numeric output: aka, 4d = ????, 8d = ????????, etc. I setup a handful of handy functions to this effect (because I couldn't figure out how to insert a var for the value) in the form of 'padnum?', such as: padnum5 () { /usr/bin/rename 's/\d+/sprintf("%05d",$&)/e' -- $@ } Which would change a file "foo-1.txt" to "foo-00001.txt"

Rename files in batch


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