Commands Reference, Volume 2

grep [ -E | -F ] [ -i ] [ -h ] [ -s ] [ -v ] [ -w ] [ -x ] [ -y ] [ [ [ -b ] [ -n ] ] | [ -c | -l | -q ] ] [ -p [ Separator ] ] { [ -e PatternList ... ] [ -f PatternFile ... ] | PatternList ... } [ File ... ]

Description

The grep command searches for the pattern 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 non-deterministic algorithm.

The grep command displays the name of the file containing 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 usually 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 may define equivalence classes for use in character ranges. If no files are specified, grep assumes standard input.

Notes:

Lines are limited to 2048 bytes.
Paragraphs (under the -p flag) are currently limited to a length of 5000 characters.
Do not run the grep command on a special file because it produces unpredictable results.
Input lines should not contain the NULL character.
Input files should end with the new-line character.
The new-line character will not be matched by the regular expressions.
Although some flags can be specified simultaneously, some flags override others. For example, the -l option takes precedence over all other flags. And if you specify both the -E and -F flags, the last one specified takes priority.

Flags

-b	Precedes each line by the block number on which it was found. Use this flag to help find disk block numbers by context. The -b flag cannot be used with input from stdin or pipes.
-c	Displays only a count of matching lines.
-E	Treats each pattern specified as an extended regular expression (ERE). A NULL value for the ERE matches every line. Note: The grep command with the -E flag is the same as the egrep command, except that error and usage messages are different and the -s flag functions differently.
-e PatternList	Specifies one or more search patterns. This works like a simple pattern but is useful when the pattern begins with a - (minus). Patterns should be separated by a new-line character. A NULL pattern can be specified by two adjacent new-line characters or a quotation mark followed by a new-line character ("\n). Each pattern is treated like a basic regular expression (BRE) unless the -E or -F flag is also specified. Multiple -e and -f flags are accepted by grep. All of the specified patterns are used when matching lines, but the order of evaluation is unspecified.
-F	Treats each specified pattern as a string instead of a regular expression. A NULL string matches every line. Note: The grep command with the -F flag is the same as the fgrep command, except that error and usage messages are different and the -s flag functions differently.
-f PatternFile	Specifies a file containing search patterns. Each pattern should be separated by a new-line character, and an empty line is considered a NULL pattern. Each pattern is treated like a basic regular expression (BRE), unless the -E or -F flag is also specified.
-h	Prevents the name of the file containing the matching line from being appended to that line. Suppresses file names when multiple files are specified.
-i	Ignores the case (uppercase or lowercase) of letters when making comparisons.

-l	Lists just the names of files (once) which contain matching lines. Each file name is separated by a new-line character. If standard input is searched, a path name of `(StandardInput)` is returned. The -l flag with any combination of the -c and -n flags behaves like the -l flag only.
-n	Precedes each line with the relative line number in the file. Each file starts at line 1, and the line counter is reset for each file processed.
-p[Separator]	Displays the entire paragraph containing matched lines. Paragraphs are delimited by paragraph separators, as specified by the Separator parameter, which are patterns in the same form as the search pattern. Lines containing the paragraph separators are used only as separators; they are never included in the output. The default paragraph separator is a blank line.
-q	Suppresses all writing to standard output, regardless of matching lines. Exits with a zero status if an input line is selected. The -q flag with any combination of the -c, -l and -n flags behaves like the -q flag only.
-s	Suppresses error messages ordinarily written for nonexistent or unreadable files. Other error messages are not suppressed.
-v	Displays all lines not matching the specified pattern.
-w	Does a word search.
-x	Displays lines that match the specified pattern exactly with no additional characters.
-y	Ignores the case of letters when making comparisons.
PatternList	Specifies one or more patterns to be used during the search. The patterns are treated as if they were specified using the -e flag.
File	Specifies a name of a file to be searched for patterns. If no File variable is given, the standard input is used.

Exit Status

This command returns the following exit values:

0	A match was found.
1	No match was found.
>1	A syntax error was found or a file was inaccessible (even if matches were found).

Examples

To use a pattern that contains some of the pattern-matching characters *, ^, ?, [, ], $, $, \{, and \}, enter:
```
grep  "^[a-zA-Z]"  pgm.s 
```
This displays every line in pgm.s whose first character is a letter.
To display all lines that do not match a pattern, enter:
grep -v "^#" pgm.s
This displays every line in pgm.s whose first character is not a # (pound sign).
To display all lines in the file1 file that match either the abc or xyz string, enter:
grep -E "abc|xyz" file1
To search for a $ (dollar sign) in the file named test2, enter:
```
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.

Files

/usr/bin/grep

Contains the grep command.

Related Information

The ed command, egrep command, fgrep command, sed command.

File Overview in AIX 5L Version 5.1 System User's Guide: Operating System and Devices.

Input and Output Redirection Overview in AIX 5L Version 5.1 System User's Guide: Operating System and Devices.

National Language Support Overview for Programming in AIX 5L Version 5.1 General Programming Concepts: Writing and Debugging Programs.

Shells Overview in AIX 5L Version 5.1 System User's Guide: Operating System and Devices.