12/7/2023 0 Comments Regular expression grep examples![]() This server is running the Linux kernel 5.16.5-arch1-1.Īs we can see, grep supports “ \d“, but we must use the right option. c: Write only a count of selected lines to standard output. GNU grep supports the -P option to interpret PCRE patterns. Therefore, if we want the grep command to match PCRE, for instance, “ \d“, we should use the -P option: $ grep -P '\d' input.txt OPTIONS -E: Match using extended regular expressions. grep 'this' demofile this line is the 1st lower case line in this file. In the following example, it displays all the line which starts with the Nov 10. The basic usage of grep command is to search for a specific string in the specified file as shown below. Beginning of line ( ) In grep command, caret Symbol matches the expression at the start of a line. ![]() Otherwise, grep will search the literal ‘|’ character. Search for the given string in a single file. ![]() Note that we shouldn’t escape the ‘|’ when we pass the -E option to grep. Let’s do the same test with the -E option: $ grep -E 'awesome|powerful' input.txt Grep allows us to use the -E option to interpret patterns as ERE. When you use regular expressions with the grep command, you need to. For example, we can match a line containing either “ awesome” or “ powerful“: $ grep 'awesome\|powerful' input.txtĪs we’ve seen in the command above, we’ve escaped the ‘|’ character to give it special meaning. These special characters, called metacharacters, also have special meaning to the system. That is to say, if we don’t set an option, it only supports BRE syntax. Grep is by default in GNU BRE matching mode.
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