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grep, egrep, fgrep - search a file for a pattern
grep [ option ] ... expression [ file ] ...
egrep [ option ] ... [ expression ] [ file ] ...
fgrep [ option ] ... [ strings ] [ file ]
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; unless
the -h flag is used, the file name is shown if there is more than one input file.
Grep patterns are limited regular expressions in the style of ed(1); it uses a compact
nondeterministic 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.
-c Only a count of matching lines is printed.
-l The names of files with matching lines are listed (once) separated by newlines.
-n Each line is preceded by its 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 No output is produced, only status.
-h Do not print filename headers with output lines.
-y Lower case letters in the pattern will also match upper case letters in the input
Same as a simple expression argument, but useful when the expression begins with a
The regular expression (egrep) or string list (fgrep) is taken from the file.
-x (Exact) only lines matched in their entirety are printed (fgrep only).
Care should be taken when using the characters $ * [ ^ | ? ' " ( ) and \ in the expression
as 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 (newline-separated) strings.
Egrep accepts extended regular expressions. In the following description `character'
A \ followed by a single character matches that character.
The character ^ ($) matches the beginning (end) of a line.
A . matches any character.
A single character not otherwise endowed with special meaning matches that charac-
A string enclosed in brackets  matches any single character from the string.
Ranges of ASCII character codes may be abbreviated as in `a-z0-9'. A ] may occur
only as the first character of the string. A literal - must be placed where it
can't be mistaken as a range indicator.
A regular expression followed by * (+, ?) matches a sequence of 0 or more (1 or
more, 0 or 1) matches of the regular expression.
Two regular expressions concatenated match a match of the first followed by a match
of the second.
Two regular expressions separated by | or newline 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
The order of precedence of operators at the same parenthesis level is  then *+? then
concatenation then | and newline.
ed(1), sed(1), sh(1)
Exit status is 0 if any matches are found, 1 if none, 2 for syntax errors or inaccessible
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.
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