grep Command

Purpose

Searches for a pattern in a file.

Syntax

grep [ -E | -F ] [ -i ] [ -h ] [ -H ] [ -L ] [ -r | -R ] [ -s ][ -u ] [ -v ] [ -w ] 
[ -x ] [ -y ] [ [ [ -b ] [ -n ] ] | [ -c | -l | -q ] ] [ -p [ Separator ] ] { [ -e PatternList ... ] [ -f PatternFile ... ] | PatternList ... } 
[ -U [ -I ] unicode_hex_notation_pattern ] [ File ... ]

Description

The grep command searches for the pattern that is specified by the Pattern parameter and writes each matching line to standard output. The patterns are limited regular expressions in the style of the ed or egrep command. The grep command uses a compact nondeterministic algorithm.

The grep command displays the name of the file that contains the matched line if you specify more than one name in the File parameter. Characters with special meaning to the shell ($, *, [, |, ^, (, ), \) must be in quotation marks when they appear in the Pattern parameter. When the Pattern parameter is not a simple string, you must enclose the entire pattern in single quotation marks. In an expression such as [a-z], the - (minus sign) cml specifies a range, according to the current collating sequence. A collating sequence might define equivalence classes for use in character ranges. If no files are specified, grep assumes standard input.

Flags

Exit Status

This command returns the following exit values:

Examples

1. To use a pattern that contains some of the pattern-matching characters *, ^, ?, [, ], \(, \), \{, and \}, enter the following command:

   grep  "^[a-zA-Z]"  pgm.s 

   This displays every line in pgm.s file whose first character is a letter.
2. To display all lines that do not match a pattern, enter the following command:

   grep   -v  "^#" pgm.s

   This displays every line in pgm.s file whose first character is not a # (pound sign).
3. To display all lines in the file1 file that match either the abc or xyz string, enter the following command:

   grep -E "abc|xyz"  file1

4. To search for a $ (dollar sign) in the test2 file, enter the following command:

   grep \\$ test2

   The \\ (double backslash) characters are necessary in order to force the shell to pass a \$ (single backslash, dollar sign) to the grep command. The \ (single backslash) character tells the grep command to treat the following character (in this example the $) as a literal character rather than an expression character. Use the fgrep command to avoid the necessity of using escape characters such as the backslash.
5. To search recursively through /tmp to find files that have the word IBM without recursing through links that points to directories, enter the following command:

   grep –R IBM /tmp

   Or

   grep –r -H IBM /tmp

6. To search recursively through /tmp to find files that have the word IBM and recurse through links as well, enter the following command:

   grep –r IBM /tmp

   Or

   grep -R -L IBM /tmp

7. To search the regex_test.txt file for the character 我, whose Unicode-defined code point is U+6211 and the hexadecimal representation is \u6211, enter the following command:

   grep -U "\u6211" regex_test.txt

   To search multiple characters, you can add a list of hexadecimal representations of the Unicode-defined code points without any space. For example, to search the characters घ and र in the regex_test.txt file, enter the following command:

   grep -U “\u0918\u0930" regex_test.txt

8. To specify a range of characters between the code points U+6200 and U+6300 to search in the regex_test.txt file, enter the following command:

   grep -U "[\u6200-\u6300]" regex_test.txt

   To specify a range of characters between the code points U+6200 and U+6300 that are also uppercase to search in the regex_test.txt file, enter the following command:

   grep -U "[\u0000-\U0010FFFF--\p{Lu}]" regex_test.txt

9. To do a loose match search of the character 𐐥, whose Unicode-defined code point is U+10425 and the hexadecimal representation is \U00010425, enter the following command:

   grep -U -I "\U00010425" regex_test.txt

10. To search the regex_test.txt file for a number with decimal digits, enter the following command:

    grep -U "\p{Nd}" regex_test.txt

    where Nd is a Unicode character property for numbers with decimal digits.
11. To search the regex_test.txt file for Hiragana characters in the Japanese language, enter the following code:

    grep -U "\p{Hiragana}" regex_test.txt

Files