NAME

egrep − search a file for a pattern using full regular expressions

SYNOPSIS

egrep [−bchilnc] −e special_expr | −f expr_file | full_regular_expression [file . . . ]

DESCRIPTION

egrep (expression grep) searches files for a pattern of characters and prints all lines that contain that pattern.  egrep uses full regular expressions (expressions that have string values that use the full set of alphanumeric and special characters) to match the patterns.  It uses a fast deterministic algorithm that sometimes needs exponential space. 

egrep accepts the same full regular expressions accepted by ed, with six exceptions:

\(\<\{m
\)\>n\}
 

(The regular expressions \( and \) should not be confused with parentheses used for grouping.)  In addition, egrep accepts the following expressions:

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

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

3.  Full regular expressions separated by │ or by a newline that match strings that are matched by any of the expressions. 

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

Be careful using the characters $, ∗, [, ^, │, (, ), and \ in full_regular_expression, because they are also meaningful to the shell.  It is safest to enclose the entire full_regular_expression in single quotes ′ . . . ′. 

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

If no files are specified, egrep assumes standard input.  Normally, each line found is copied to the standard output.  The filename is printed before each line found if there is more than one input file. 

Command line options are:

−b Precede each line by the block number on which it was found.  This can be useful in locating block numbers by context (first block is 0). 

−c Print only a count of the lines that contain the pattern. 

−i Ignore uppercase/lowercase distinction during comparisons.  This option is valid only for single byte characters. 

−h Suppress printing of filenames when searching multiple files. 

−l Print the names of files with matching lines once, separated by newlines.  Does not repeat the names of files when the pattern is found more than once. 

−n Precede each line by its line number in the file (first line is 1). 

−v Print all lines except those that contain the pattern. 

−e special_expr
Search for a special_expr (full_regular_expression that begins with a −). 

−f expr_file
Take the list of full_regular_expressions from expr_file.

INTERNATIONAL FUNCTIONS

egrep can process characters from supplementary code sets.  In regular expressions, searches are performed on characters, not on individual bytes. 

SEE ALSO

ed(1), fgrep(1), grep(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 (even if matches were found). 

NOTES

Ideally there should be only one grep command, but there is not a single algorithm that spans a wide enough range of space-time tradeoffs.  Lines are limited to BUFSIZ characters; longer lines are truncated.  BUFSIZ is defined in /usr/include/stdio.h.

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