A word character is any alphabet (irrespective of case), digit and the underscore character. The second type of restriction is word anchors. $ printf 'spared no one\npar\nspar\ndare' | grep -x 'par' $ printf 'spared no one\npar\nspar\ndare' | grep '^par$' You can combine these two anchors to match only whole lines. Here are some examples: $ cat anchors.txt $ metacharacter restricts the matching to the end of the line.^ metacharacter restricts the matching to the start of the line.In case you need to match those characters literally, you need to escape them with a \ (discussed in the Escaping metacharacters section). The characters with special meaning are known as metacharacters in regular expressions parlance. These restrictions are made possible by assigning special meaning to certain characters and escape sequences.
#GREP REGEX REFERENCE HOW TO#
In later sections and chapters, you'll get to know how to define your own rules for restriction. For now, you'll see the ones that are already part of BRE/ERE. Instead of matching anywhere in the line, restrictions can be specified.
See also POSIX specification for BRE and ERE. See grep manual: Problematic Regular Expressions if you are working on portable scripts. The example_files directory has all the files used in the examples. -P if available, this option will enable Perl Compatible Regular Expression (PCRE).-F option will cause the search patterns to be treated literally.in GNU grep, BRE and ERE only differ in how metacharacters are specified, no difference in features.-E option will enable Extended Regular Expression (ERE).-G option can be used to specify explicitly that BRE is needed.Here are the various options available to choose a particular flavor: GNU grep also supports Perl Compatible Regular Expressions, which will be discussed in a later chapter.īy default, grep treats the search pattern as Basic Regular Expression (BRE). Unless otherwise indicated, examples and descriptions will assume ASCII input. This chapter covers Basic and Extended Regular Expressions as implemented in GNU grep.
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