egrep [-cinv] [-e expression] [-f filename] [expression] [filename]

egrep searches the input filename (the standard input default) for lines
matching a regular expression. Normally, each matching line is copied to the
standard output.

Take care when using the characters `$', `*', `[', `^', `|', `(', `)', `\',
and space in the expression, as these characters are also meaningful to the
shell. It is safest to enclose the entire expression argument in single
quotes '...', or to put the expression into a file and use the `-f' option.

-c	Display a count of matching lines rather than displaying the lines
	which match.

-i	Ignore the case of letters in making comparisons - that is, upper
	and lower case are considered identical.

-n	Precede each line by its relative line number in the file.

-v	Invert the search to only display lines that do not match.

-e expression
	Same as a simple expression argument, but useful when the expression
	begins with a `-'.

-f filename
	Take the regular expression from filename.

REGULAR EXPRESSIONS

The following regular expressions match a single character:

c	An ordinary character (not one of the special characters discussed
	below) matches that character.

\c	A backslash (\) followed by any special character matches the
	special character itself. The special characters are:

	`.', `*', `[', and `\'
		which are always special, except when they appear within
		square brackets ([]).

	`^'	which is special at the beginning of an entire regular
		expression, or when it immediately follows the left of a
		pair of square brackets ([]).

	`$'	which is special at the end of an entire regular expression.

.	A regular expression that matches any character except NEWLINE.

[string]
	A non-empty string of characters enclosed in square brackets matches
	any one character in that string.

	If, however, the first character of the string is a `^' the regular
	expression matches any character except NEWLINE and the remaining
	characters in the string. The `^' has this special meaning only if
	it occurs first in the string.

	The `-' may be used to indicate a range of consecutive ASCII
	characters; for example, [0-9] is equivalent to [0123456789]. The
	`-' loses this special meaning if it occurs first (after an initial
	`^', if any) or last in the string.

	The `]' does not terminate such a string when it is the first
	character within it (after an initial `^', if any); that is, []a-f]
	matches either `]' or one of the letters a through f inclusive.

	The four characters `.', `*', `[', and `\' stand for themselves
	within such a string of characters.

The following rules may be used to construct regular expressions:

Concatenation
	The concatenation of regular expressions matches the concatenation
	of the strings matched by each component of the regular expression.

^	at the beginning of an entire regular expression constrains that
	regular expression to match an initial segment of a line.

$	at the end of an entire regular expression constrains that regular
	expression to match a final segment of a line.

The construction
	example% ^entire regular expression$
constrains the entire regular expression to match the entire line.

	*	A regular expression followed by `*' matches zero or more
		occurrences of the regular expression. If there is any
		choice, the longest leftmost string that permits a match is
		chosen.

	+	A regular expression followed by `+' matches one or more
		occurrences of the regular expression. If there is any
		choice, the longest leftmost string that permits a match is
		chosen.

	?	A regular expression followed by `?' matches zero or one
		occurrences of the regular expression. If there is any
		choice, the longest leftmost string that permits a match is
		chosen.

	|	Alternation: two regular expressions separated by `|' match
		either a match for the first or a match for the second.

	()	A regular expression enclosed in parentheses matches a match
		for the regular expression.

The order of precedence of operators at the same parenthesis level is `[ ]'
(character classes), then `*' `+' `?' (closures), then concatenation, then
`|' (alternation). However, I would strongly encourage you to use parentheses
rather than relying on these precedence rules.

EXAMPLES

Search a file for a fixed string:
	example% egrep intro /usr/share/man/man3/*.3*

Look for character classes:
	example% egrep '[1-8]([CJMSNX])' /usr/share/man/man1/*.1

Look for alternative patterns:
	example% egrep '(Sally|Fred) (Smith|Jones|Parker)' telephone.list