a pattern or an re may also be referred to as a string. the term match is used to describe a string in a file (or standard input) that is successfully specified by a pattern or re. the terms pattern and regular expression can be used interchangeably. The term regular expression, or re, is used when there is no need to distinguish between bres and eres. nonetheless, the grep command is used illustratively here. thus the rules described below are applicable in many contexts. there is much in common between bres and eres, but there are important differences as well.ДЄ variety of commands and utilities use one or the other type of re, or both. the two types of a regular expression that can be built by using these rules are termed either basic regular expression ( bre) or extended regular expression ( ere). On digital unix (and xpg4 conforming systems) there are two standard types of res, and thus two sets of rules for building patterns. this section explains the rules for constructing such patterns. Regular expressions ( re's) provide a powerful way to specify patterns to search for in text files (or in the standard input). o file) produces unpredictable results and is discouraged. Running grep on a non-text file (for example, an. when using the c shell interactively, you must enter a backslash before terminating a line in a multiline pattern. in some cases, such as in multiline pattern lists and subexpressions, quoting is essential. You are strongly encouraged to single quote patterns to protect them from unwanted shell substitutions. In the output of the grep command, a matched line is preceded with the name of the file in which it was found if you specify more than one file (except when the -h flag is specified). see discussion of regular expressions, below.

with the -f flag, the pattern is considered a fixed string. with the -e flag, the pattern is treated as an extended regular expression ( ere). x displays a line only if the pattern matches the entire line.Д«y default, the grep command treats a pattern as a basic regular expression ( bre). a word is any string of alphanumeric characters (letters, numerals, and underscores) delimited by nonalphanumeric characters (punctuation or white space) or by the beginning or end of the line). w matches only if the expression is found as a separate word in the text. useful for filtering unwanted lines out of a file. v displays all lines except those that match the specified pattern. other error messages are still displayed. s suppresses error messages arising from non-existent or unreadable files. q suppresses all output except error messages. the default paragraph separator is a blank line. lines containing the paragraph separators are used only as separators they are never included in the output. paragraphs are delimited by paragraph separators, paragraph_ separator, which are patterns in the same form as the search pattern. n precedes each line with its relative line number in the file.Дisplays the entire paragraph containing matched lines. grep returns (standard input) (or the local equivalent) in place of a filename if -l is specified with standard input. each filename is listed only once filenames are separated by newline characters. l lists only the name of each file containing matched lines. i ignores the case of letters pattern matching that is, uppercase and lowercase in the input are considered to be identical.

h suppresses reporting of filenames when multiple files are processed. Specifies a file that contains patterns to match, one per line. the -e flag is useful for specifying a pattern that begins with a - (dash). if more than one pattern is specified in pattern_ list, they must be separated by newline characters (carriage returns). Used to specify one or more patterns to match. c displays only a count of matching lines. use this flag to help find disk block numbers by context. b precedes each line by the block number on which it was found. f treats patterns as fixed strings and is equivalent to the obsolescent fgrep command. e treats patterns as extended regular expressions and is equivalent to the obsolescent egrep command. for example, if you specify -n and -l, the output includes filenames only (as specified by -l) and thus does not include line numbers (as specified by -n).

The grep command searches the specified files (standard input by default) for lines containing characters that match the specified patterns, and then writes matching lines to standard output.ДЄlthough most flags can be combined, some combinations result in one flag overriding another. The commands grep -e and grep -f are equivalent to the obsolescent commands egrep and fgrep, respectively. Name grep, egrep, fgrep - searches a file for patterns

Grep not include