agrep?searches the input?file names?(standard input?is the default) for records containing?strings?which either exactly or approximately match a?pattern.

A?record?is by default a single line, but it can be defined differently using the?-d?option (see below). Normally, each record found is copied to the standard output.?Approximate matching?allows finding records that contain the pattern with several errors including?substitutions,?insertions, and?deletions.

For example, "Massechusets" matches "Massachusetts" with two errors (one?substitution?and one?insertion). Running?agrep -2 Massechusets foo?outputs all lines in the file?foo?containing any string with (at most) 2 errors from "Massechusets".

agrep?supports many kinds of?queries?including arbitrary?wildcards,?sets?of patterns, and in general, all?regular expressions. It supports most of the options supported by the?grep?family plus several more (but it is not 100% compatible with?grep).

As with the rest of the?grep?family, the?characters?$,?^,?*,?[,?],?^,?|,?(,?),?!, and?\?can cause unexpected results when included in the pattern, as these special characters are also meaningful to the?shell. To avoid these problems, one should always enclose the entire pattern argument in single quotes, i.e.,?'pattern'. Do not use double quotes (").

When?agrep?is applied to more than one input file, the name of the file is displayed at the beginning of each line which matches the pattern. (The file name is not displayed when processing a single file, but in that case if the user wants the file name to appear, they should use?/dev/null?as a second file in the list, and then the file name will be displayed).

agrep [ -#cdehiklnpstvwxBDGIS ] pattern [ -f patternfile ] [ filename... ]

agrep?supports a large variety of patterns, including simple strings, strings with classes of characters, sets of strings, wildcards, and regular expressions.

Strings

A?string?is any sequence of characters, including the special symbols?^?for beginning of line and?$?for end of line. The special characters listed above (?$,?^,?*,?[,?^,?|,?(,?),?!, and?\?) should be preceded by?\?if they are to be matched as regular characters. For example,?\^abc\\?corresponds to the string "^abc\", whereas?^abc?corresponds to the string "abc" at the beginning of a line.

Character classes

A?class?of characters is a list of characters inside "[]" (in order) corresponds to any character from the list, where a dash represents the range between two characters. For example,?[a-ho-z]?is any character between?a?and?h?or between?o?and?z. The symbol?^?inside?[]?denotes which characters not to match ("complements" the list). For example,?[^i-n]?denotes any character except characters?i?through?n. The symbol?^?thus has two meanings, but this is consistent with egrep. The symbol?.?stands for any character except for the newline character.

Boolean operations

agrep?supports an?AND?operation?';' and an?OR?operation ',', but not a combination of both. For example,?fast;network?searches for all records containing both "fast" and "network".

Wildcards

The symbol '#' is used to denote a wildcard.?#?matches zero,?or any number of,?arbitrary characters. For example,?ex#e?matches "example". The symbol?#?is equivalent to?.*?in egrep. In fact,?.*?will work too, because it is a valid regular expression, but unless this is part of an actual regular expression,?#?will work faster.

Combination of Exact and Approximate Matching

any pattern inside angle brackets?<>?must match the text exactly even if the match is with errors. For example,?ics?matches?mathematical?with one error (replacing the last?s?with an?a), but?mathe?does not match?mathematical?no matter how many errors we allow.

Regular Expressions

The syntax of regular expressions in?agrep?is in general the same as that for?egrep. The union operation '|', Kleene closure '*', and parentheses?()?are all supported. Currently '+' is not supported. Regular expressions are currently limited to approximately 30 characters (excluding meta characters). Some options (-d,?-w,?-f,?-t,?-x,?-D,?-I,?-S) do not currently work with regular expressions. The maximal number of errors for regular expressions that use '*' or '|' is 4.

agrep -2 -c ABCDEFG foo

Gives the number of lines in file foo that contain "ABCDEFG" within two errors.

agrep -1 -D2 -S2 'ABCD#YZ' foo

Outputs the lines containing "ABCD" followed within arbitrary distance by "YZ", with up to one additional insertion (-D2?and?-S2?make deletions and substitutions too "expensive").

agrep -5 -p abcdefghij /path/to/dictionary/words

Outputs the list of all words in the dictionary located at?/path/to/dictionary/words?containing at least 5 of the first 10 letters of the alphabet in order.

agrep -1 'abc[0-9](de|fg)*[x-z]' foo

Outputs the lines containing, within up to one error, the string that starts with "abc" followed by one digit, followed by zero or more repetitions of either "de" or "fg", followed by either "x", "y", or "z".

agrep -d '^From ' 'breakdown;internet' mbox

Outputs all mail messages (the pattern "^From?" separates mail messages in a mail file) that contain keywords "breakdown" and "internet".

agrep -d '$$' -1 '' foo

Finds all paragraphs that contain?word1?followed by?word2?with one error in place of the blank. In particular, if?word1?is the last word in a line and?word2?is the first word in the next line, then the space will be substituted by a newline symbol and it will match. Thus, this is a way to overcome separation by a newline. Note that?-d '$$'?(or another?delim?which spans more than one line) is necessary, because otherwise?agrep?searches only one line at a time.