How does grep search

Skip to content. Change Language. Related Articles. Table of Contents. Save Article. Improve Article. Like Article. Previous 'crontab' in Linux with Examples. Recommended Articles. Article Contributed By :. Easy Normal Medium Hard Expert. Connect and share knowledge within a single location that is structured and easy to search. It can return the lines where it finds a match or the lines where it doesn't. You tagged your question with grep tag. But it was better if you read first the tag info referring to grep :.

A common use for grep is to locate and print out certain lines from log files or program output. See this Ubuntu Documentation page for more information on how to use grep. Even more, you can get information about grep using one of these commands: info grep , grep -h , grep --help , whatis grep or apropos grep. The easiest way to use it is something like grep "word" file. To make it do more advanced things, learn about regular expressions. You can find plenty of tutorials online by searching.

Personally, I don't recommend using the terminal just for the sake of using the terminal. You might go through a lot of trouble to learn complicated tools like grep only to discover that you use graphical programs or scripts you wrote in your favorite interpreted language. Most people who recommend learning old-fashioned terminal commands are themselves old-fashioned hackers. The grep command searches one or more input files for lines containing a match to a specified pattern.

By default, grep prints the matching lines. In addition, two variant programs egrep and fgrep are available. Egrep is the same as grep -E. Fgrep is the same as grep -F. Man Page. Ubuntu Community Ask! Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

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This chapter describes how to search directories and files for keywords and strings by using the grep command. To search for a particular character string in a file, use the grep command. The basic syntax of the grep command is:. In this example, string is the word or phrase you want to find, and file is the file to be searched. A string is one or more characters. A single letter is a string, as is a word or a sentence. Strings can include blank spaces, punctuation, and invisible control characters.

For example, to find Edgar Allan Poe's telephone extension, type grep , all or part of his name, and the file containing the information:. Note that grep failed in the first try because none of the entries began with a lowercase a. You can use the grep command as a filter with other commands, enabling you to filter out unnecessary information from the command output.

To use grep as a filter, you must pipe the output of the command through grep. The second part of the command line pipes that list through grep , looking for the pattern Sep.

To find a pattern that is more than one word long, enclose the string with single or double quotation marks. The grep command can search for a string in groups of files. When it finds a pattern that matches in more than one file, it prints the name of the file, followed by a colon, then the line matching the pattern.