Content-type: text/html Man page of regex


Section: FMLI Commands (1F)
Updated: 12 Jul 1999
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regex - match patterns against a string  


regex [-e] [ -v "string"] [ pattern template] ... pattern [template]  


The regex command takes a string from the standard input, and a list of pattern / template pairs, and runs regex() to compare the string against each pattern until there is a match. When a match occurs, regex writes the corresponding template to the standard output and returns TRUE. The last (or only) pattern does not need a template. If that is the pattern that matches the string, the function simply returns TRUE. If no match is found, regex returns FALSE.

The argument pattern is a regular expression of the form described in regex(). In most cases, pattern should be enclosed in single quotes to turn off special meanings of characters. Note that only the final pattern in the list may lack a template.

The argument template may contain the strings $m0 through $m9, which will be expanded to the part of pattern enclosed in ( ... )$0 through ( ... )$9 constructs (see examples below). Note that if you use this feature, you must be sure to enclose template in single quotes so that FMLI does not expand $m0 through $m9 at parse time. This feature gives regex much of the power of cut(1), paste(1), and grep(1), and some of the capabilities of sed(1). If there is no template, the default is $m0$m1$m2$m3$m4$m5$m6$m7$m8$m9.  


The following options are supported:

-e Evaluates the corresponding template and writes the result to the standard output.

-v "string" Uses string instead of the standard input to match against patterns.



Example 1: Cutting letters out of a string

To cut the 4th through 8th letters out of a string (this example will output strin and return TRUE):

`regex -v "my string is nice" '^.{3}(.{5})$0' '$m0'`

Example 2: Validating input in a form

In a form, to validate input to field 5 as an integer:

valid=`regex -v "$F5" '^[0-9]+$'`

Example 3: Translating an environment variable in a form

In a form, to translate an environment variable which contains one of the numbers 1, 2, 3, 4, 5 to the letters a, b, c, d, e:

value=`regex -v "$VAR1" 1 a 2 b 3 c 4 d 5 e '.*' 'Error'`

Note the use of the pattern '.*' to mean "anything else".

Example 4: Using backquoted expressions

In the example below, all three lines constitute a single backquoted expression. This expression, by itself, could be put in a menu definition file. Since backquoted expressions are expanded as they are parsed, and output from a backquoted expression (the cat command, in this example) becomes part of the definition file being parsed, this expression would read /etc/passwd and make a dynamic menu of all the login ids on the system.

`cat /etc/passwd | regex '^([^:]*)$0.*$' '
action=`message "$m0 is a user"`'`


If none of the patterns match, regex returns FALSE, otherwise TRUE.  


Patterns and templates must often be enclosed in single quotes to turn off the special meanings of characters. Especially if you use the $m0 through $m9 variables in the template, since FMLI will expand the variables (usually to "") before regex even sees them.

Single characters in character classes (inside []) must be listed before character ranges, otherwise they will not be recognized. For example, [a-zA-Z_/] will not find underscores (_) or slashes (/), but [_/a-zA-Z] will.

The regular expressions accepted by regcmp differ slightly from other utilities (that is, sed, grep, awk, ed, and so forth).

regex with the -e option forces subsequent commands to be ignored. In other words, if a backquoted statement appears as follows:

`regex -e ...; command1; command2`

command1 and command2 would never be executed. However, dividing the expression into two:

`regex -e ...``command1; command2`

would yield the desired result.  


See attributes(5) for descriptions of the following attributes:




awk(1), cut(1), grep(1), paste(1), sed(1), regcmp(3C), attributes(5)




This document was created by man2html, using the manual pages.
Time: 02:38:39 GMT, October 02, 2010