![]() ![]() $ grep "lines.*empty" demo_fileįrom documentation of grep: A regular expression may be followed by one of several repetition operators: i.e To search “linesempty” in the demo_file. In the following example, it searches for all the pattern that starts with “lines” and ends with “empty” with anything in-between. This is a very powerful feature, if you can use use regular expression effectively. Match regular expression in files Syntax: So it matches all the words such as “the”, “THE” and “The” case insensitively as shown below.Īnd this is the last line. This searches for the given string/pattern case insensitively. ![]() Case insensitive search using grep -i Syntax: $ cp demo_file demo_file1ĭemo_file:this line is the 1st lower case line in this file.ĭemo_file:Two lines above this line is empty.ĭemo_file1:this line is the 1st lower case line in this file.ĭemo_file1:Two lines above this line is empty.ĭemo_file1:And this is the last line. When the Linux shell sees the meta character, it does the expansion and gives all the files as input to grep. The grep output will also include the file name in front of the line that matched the specific pattern as shown below. For this example, let us copy the demo_file to demo_file1. This is also a basic usage of grep command. Checking for the given string in multiple files. The basic usage of grep command is to search for a specific string in the specified file as shown below. Search for the given string in a single file This Line Has All Its First Character Of The Word With Upper Case.Īnd this is the last line. This line is the 1st lower case line in this file. THIS LINE IS THE 1ST UPPER CASE LINE IN THIS FILE. In this article let us review 15 practical examples of Linux grep command that will be very useful to both newbies and experts.įirst create the following demo_file that will be used in the examples below to demonstrate grep command. Earlier we discussed 15 practical examples for Linux find command, Linux command line history and mysqladmin command. This is part of the on-going 15 Examples series, where 15 detailed examples will be provided for a specific command or functionality. The grep command lists the lines that contain a match.You should get a grip on the Linux grep command. For example, "words" that begin with a digit would not match. This regular expression matches any "word" that begins with a letter (upper or lower case). Here is an example of a regular expression search: grep "\" file It matches any single character in that list if the first character of the list is the caret ^ then it matches any character not in the list The preceding item in the regular expression will be matched zero or more timesĪ bracket expression is a list of characters enclosed by. Here is a list of some of the special characters used to create a regular expression: Grep can search for complicated patterns to find what you need. Double quotes could also have been used in this example. Quotes are not usually essential, but in this example they are essential because the name contains a space. Notice the use of quotes in the above command. The above command searches all files in the current directory for the name and lists all lines that contain a match. This can be easily accomplished as follows: grep 'Nicolas Kassis' * A cool example of using grep with multiple files would be to find all lines in all files in a given directory that contain the name of a person. The above command only looks at one file. This is OK but it does not show the true power of grep. The above command searches the file for STRING and lists the lines that contain a match. In the simplest case grep can be invoked as follows: grep 'STRING' filename It can be used with a regular expression to be more flexible at finding strings. ![]() Grep is a command-line tool that allows you to find a string in a file or stream. ![]()
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