NAME

grep, egrep, fgrep − search a file for a pattern

SYNOPSIS

grep [ options ] expression [ files ]

egrep [ options ] [ expression ] [ files ]

fgrep [ options ] [ strings ] [ files ]

DESCRIPTION

Commands of the grep family search the input files (standard input default) for lines matching a pattern.  Normally, each line found is copied to the standard output.  Grep patterns are limited regular expressions in the style of ed(1); it uses a compact non-deterministic algorithm. Egrep patterns are full regular expressions; it uses a fast deterministic algorithm that sometimes needs exponential space. Fgrep patterns are fixed strings; it is fast and compact. The following options are recognized:

−v All lines but those matching are printed. 

−x (Exact) only lines matched in their entirety are printed (fgrep only). 

−c Only a count of matching lines is printed. 

−l Only the names of files with matching lines are listed (once), separated by new-lines. 

−n Each line is preceded by its relative line number in the file. 

−b Each line is preceded by the block number on which it was found.  This is sometimes useful in locating disk block numbers by context. 

−s The error messages produced for nonexistent or unreadable files are suppressed (grep only). 

−e expression
Same as a simple expression argument, but useful when the expression begins with a − (does not work with grep).

−f file The regular expression (egrep) or strings list (fgrep) is taken from the file.

In all cases, the file name is output if there is more than one input file.  Care should be taken when using the characters $, *, [, ^, │, (, ), and \ in expression, because they are also meaningful to the shell. It is safest to enclose the entire expression argument in single quotes ′...′. 

Fgrep searches for lines that contain one of the strings separated by new-lines. 

Egrep accepts regular expressions as in ed(1), except for \( and \), with the addition of:

1.  A regular expression followed by + matches one or more occurrences of the regular expression. 

2.  A regular expression followed by ?  matches 0 or 1 occurrences of the regular expression. 

3.  Two regular expressions separated by │ or by a new-line match strings that are matched by either. 

4.  A regular expression may be enclosed in parentheses () for grouping. 

The order of precedence of operators is [], then ∗?+, then concatenation, then │ and new-line. 

SEE ALSO

ed(1), sed(1), sh(1). 

DIAGNOSTICS

Exit status is 0 if any matches are found, 1 if none, 2 for syntax errors or inaccessible files. 

BUGS

Ideally there should be only one grep, but we don’t know a single algorithm that spans a wide enough range of space-time tradeoffs.
Lines are limited to 256 characters; longer lines are truncated.
Egrep does not recognize ranges, such as [a−z], in character classes. 

May 16, 1980