Full Regular Expressions

In the following description `character' excludes newline:

1.

A \ followed by a single character matches that character.

2.

The character ^ ($) matches the beginning (end) of a line as an anchor.

3.

A . matches any character.

4.

A single character not otherwise endowed with special meaning matches that character.

5.

A string enclosed in brackets [] forms a bracket expression that 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.

6.

A regular expression followed by * (+, ?) matches a sequence of 0 or more (1 or more, 0 or 1) matches of the regular expression.

7.

Two regular expressions concatenated match a match of the first followed by a match of the second.

8.

Two regular expressions separated by | or newline match either a match for the first or a match for the second (alternation).

9.

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

The order of precedence of operators is [] then () then *+? then concatenation then | and newline.

Extended Regular Expressions

Extended Regular Expressions add the following features to Full Regular Expressions:

10.

A regular expression followed by {m,n} forms an interval expression that matches a sequence of m through n matches, inclusive, of the regular expression. The values of m and n must be non-negative and smaller than 255. The form {m} matches exactly m occurrences, {m,} matches at least m occurrences.

11.

In bracket expressions as described in 5., the following character sequences are considered special:

Character class expressions of the form [:class:]. In the C LC_CTYPE locale, the classes

[:alnum:]	[:cntrl:]	[:lower:]	[:space:]
[:alpha:]	[:digit:]	[:print:]	[:upper:]
[:blank:]	[:graph:]	[:punct:]	[:xdigit:]

are recognized; further locale-specific classes may be available. A character class expression matches any character that belongs to the given class in the current LC_CTYPE locale.

Collating symbol expressions of the form [.c.], where c is a collating symbol in the current LC_COLLATE locale. A collating symbol expression matches the specified collating symbol.

Equivalence class expressions of the form [=c=], where c is a collating symbol in the current LC_COLLATE locale. An equivalence class expression matches any character that has the same collating weight as c.

The order of precedence of operators is [==] [::] [..] then [] then () then *+? {m,n} then concatenation then ^ $ then | and newline.

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 ´ ´.

Both /usr/5bin/egrep and /usr/5bin/posix/egrep accept the following options:

-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. Block numbers start with 0.

-c

Only a count of matching lines is printed.

-e pattern_list

Specifies one or more patterns, separated by newline characters. A line is selected if one or more of the specified patterns are found.

-f pattern_file

One or more patterns, separated by newline characters, are read from pattern_file. If multiple -e or -f options are supplied to /usr/5bin/posix/egrep, all of the pattern lists will be evaluated.

-h

Normally, the name of each input file is printed before a match if there is more that one input file. When this option is present, no file names are printed.

-i

Upper- and lowercase differences are ignored when searching matches.

-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. Line numbers start with 1.

-v

All lines but those matching are printed.

The following options are supported by /usr/5bin/posix/egrep only:

-q

Do not write anything to standard output.

-s

Error messages for nonexistent or unreadable files are suppressed.

-x

Consider only lines consisting of the pattern as a whole, like a regular expression surrounded by ^ and $.

The following options are supported as extensions:

-r

With this option given, egrep does not directly search in each given file that is a directory, but descends it recursively and scans each regular file found below it. Device files are ignored. Symbolic links are followed.

-R

Operates recursively as with the -r option, but does not follow symbolic links that point to directories unless if they are explicitly specified as arguments.

-z

If an input file is found to be compressed with compress(1), gzip(1), or bzip2(1), the appropriate compression program is started, and egrep searches for the pattern in its output.