The command "egrep" searches its input for lines containing the string specified by "keyword." Any lines containing a match are reported on the standard output. If one or more file names are supplied as arguments, the data forks of the files will be opened and their contents used as input. If no file names are supplied, "egrep" will read from its standard input. If more than one file name is supplied, "egrep" will also report the name of the file in which the match occurred
REGULAR EXPRESSIONS
Standard egrep style regular expressions are supported. The regular expression code is by Henry Spencer, Copyright (c) 1986 by University of Toronto. The following rules describe the formation of regular expressions. (Quoted directly from documentation provided by Henry Spencer.)
A regular expression is zero or more branches, separated by `|'. It matches anything that matches one of the branches.
A branch is zero or more pieces, concatenated. It matches a match for the first, followed by a match for the second, etc.
A piece is an atom possibly followed by `*', `+', or `?'. An atom followed by `*' matches a sequence of 0 or more matches of the atom. An atom followed by `+' matches a sequence of 1 or more matches of the atom. An atom followed by `?' matches a match of the atom, or the null string.
An atom is a regular expression in parentheses (matching a match for the regular expression), a range (see below), `.' (matching any single character), `^' (matching the null string at the beginning of the input string), `$' (matching the null string at the end of the input string), a `\' followed by a single character (matching that character), or a single character with no other significance (matching that character).
A range is a sequence of characters enclosed in `[]'. It normally matches any single character from the sequence. If the sequence begins with `^', it matches any single character _n_o_t from the rest of the sequence. If two characters in the sequence are separated by `-', this is shorthand for the full list of ASCII characters between them (e.g. `[0-9]' matches any decimal digit). To include a literal `]' in the sequence, make it the first character (following a possible `^'). To include a literal `-', make it the first or last character.
AMBIGUITY
If a regular expression could match two different parts of the input string, it will match the one which begins earliest. If both begin in the same place but match different lengths, or match the same length in different ways, life gets messier, as follows.
In general, the possibilities in a list of branches are considered in left-to-right order, the possibilities for `*', `+', and `?' are considered longest-first, nested constructs are considered from the outermost in, and concatenated constructs are considered leftmost-first. The match that will be chosen is the one that uses the earliest possibility in the first choice that has to be made. If there is more than one choice, the next will be made in the same manner (earliest possibility) subject to the decision on the first choice. And so forth.
For example, `(ab|a)b*c' could match `abc' in one of two ways. The first choice is between `ab' and `a'; since `ab' is earlier, and does lead to a successful overall match, it is chosen. Since the `b' is already spoken for, the `b*' must match its last possibility-the empty string-since it must respect the earlier choice.
In the particular case where no `|'s are present and there is only one `*', `+', or `?', the net effect is that the longest possible match will be chosen. So `ab*', presented with `xabbbby', will match `abbbb'. Note that if `ab*' is tried against `xabyabbbz', it will match `ab' just after `x', due to the begins-earliest rule. (In effect, the decision on where to start the match is the first choice to be made, hence subsequent choices must respect it even if this leads them to less-preferred alternatives.)
OPTIONS
The behavior of "egrep" can be altered through the use of the following option:
-v Egrep will report lines in which a match is NOT found instead of the lines in which a match is found, if the option -v is given.
RESTRICTIONS
Files created by some Macintosh applications consist of very long lines, and may contain binary data interspersed with text. The utilities "seg" and "xn" have been provided to partially combat content searching problems which may arise from these facts.
SEE ALSO
grep, seg, xn
AUTHOR
Regular expressions by Henry Spencer, Copyright (c) 1986 by University of Toronto.
