UGN Security Forums UGN Security: Knowledge Base Operating Systems *nix & *nix Security Purpose of grep

I know what it does, but how is it useful? Maybe I didn't really read it right but "The grep command searches for a patern of characters in a file or multiple files" So if you already know what files you are looking in to find your characters why would grep be useful?

I think I figured it out. It's like if
you thought there was an error in a passwd file you could use grep to try to find the file. Am I close.

I use it a lot in concert with commands that can have a lot of output to STDOUT: ie, if I want to know if a certain process is running I do a:

ps -ax | grep init

or if you have a huge dir and are looking for a specific file:

ls | grep .txt

And even if you are ripping through config files and need to know a certain parameter:

cat /etc/somthing.conf | grep VARIABLE=

There are a ton of uses for it, but that's what I find I use it for the most.

Infinite

grep is one of the sweetest tools :]
Pretty much what Infinite said, its a Search tool.


Quote from Grep GNU Project Website:

Well, depending on what you are doing grep can be one of the most usfull tools. I used to leave nmap on for hours doing random port scans of stuff I was interested in and logging it to a file and then I hate a perl script that would extract ip addresses that had that port open and run further test to see if the system was vulnerable to a certain bug. Grep was helpful in every step of the way. Anytime you have big logfiles grep is a lifesaver.

Maybe I don't understand the use of the word pattern. Could someone explain or point me to a tutorial?

http://sitescooper.org/tao_regexps.html

And on't forget man grep

Perfect, Thank You.

My most common uses are for going through config files, error reports and logs.

dmesg | grep (hardware device)

usefull for finding hardware errors in your kernel

cat /var/log/Xorg.cong | grep EE

Useful for finding errors in your xorg.conf file. Try it with WW to find the warnings to iron them out if your a perfectionist. Or it might be /var/log/XFree86.0.log if you're slow on the update tip.

The -A and -B flags are useful for specifiy how many lines you want to display after and before the occurence of the pattern.

I'm sure there are plenty more very useful functions for this amazing utility. Grep has been around since the begining of unix for good reason. It is even on this system from 1970 I'm working on right now.

HERE you have a very basic grep tutorial written by me a couple of years ago.