Grep CheatSheet

grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. Its name comes from the ed command g/re/p (globally search for a regular expression and print matching lines), which has the same effect.

grep was originally developed for the Unix operating system, but later available for all Unix-like systems and some others such as OS-9.

'grep' command is the prime weapon in the war zone of Linux. Once you master the GREP command, you should get the tons of benefits out of it.

1. Saves time over finding the required configuration
2. Solves the problem related to the troubleshooting more quickly
3. Help for debugging the code more quickly
4. Finding out the blank files and folders in Linux

Most people imagine that system administrators and programmers fiddle with knobs and diodes. Their goal? To reach into the virtual reality of the Internet, gathering the binary forces of code into the applications and infrastructure we all use today. Most people would be disappointed to learn that sysadmins and code monkeys more often poke at streams of text in hopes of getting the right response.

If you are a sysadmin or programmer and find yourself obsessively dipping into streams of text on a POSIX system, then you have probably either encountered grep or come across a time you wished you could use this command.

Its quite easy to make use of the grep command in your Linux- or UNIX-based system. As you might already have an idea that for using this command, you need to open the terminal on your system.

Now to use the grep command, the first thing you need to do is to understand its syntax, which is as follows:

grep [OPTION]  PATTERNS  [FILE]

• OPTIONS - Defines the way the grep will behave while searching for a text or string.
• PATTERNS - The text pattern or the regular expressions that need to be searched.
• FILE - It specifies one or more files in which the pattern will be searched.

We assume, a Security analyst is troubleshooting the logs for a recent attack. In this use case, the analyst may have around GBs, which takes an ample amount of time to troubleshoot the issue. By that time, your website is down, that impact is different.

However, Using the grep command Security Analyst can easily find out the required set of logs with the Parameter he/she searching in the captured logs, that too in a brief period.

# Search standard output (i.e. a stream of text)
$ grep [options] search_string


# Search for an exact string in file:
$ grep [options] search_string path/to/file


# Print lines in bestforstudy.txt containing the string "bestforstudy"
$ grep 'bestforstudy' bestforstudy.txt

The abbreviation grep stands for Global Regular Expression Print. This is one of the most widely used commands in the Linux world. Approx., 90% of users, use the grep command to find the matching pattern/string in a file. However, we always miss the real power of the grep command. The regular expression capability makes it one of the prime commands of the Linux world. Which helps a lot to process the data or analyze the broad set of logs.

A tool like grep is indeed extremely useful, not to mention indispensable, for looking through a multitude of text files, scripts, and especially logs for specific patterns with considerable ease. You can look for one or several patterns in a single file or many files, or use them to filter out the lines from those files containing those patterns.

You can even make use of pipes for more complicated searches and filtering using grep. It is well worth the time to learn more about this excellent command, especially some of its advanced features.

• All RegEX syntax (bestforstudy.com)
• RegEX Example (bestforstudy.com)