regex(1fmli)

regex -- match patterns against a string

Synopsis

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

Description

The regex command takes a string from ``standard input'', and a list of pattern/template pairs, and runs the regex function defined in regcmp(3G) to compare the string against each pattern until there is a match. When a match occurs, regex writes the corresponding template to ``stdout''. The last (or only) pattern does not need a template. If that pattern matches the string, regex returns TRUE. If no match is found, regex returns FALSE.

-e: means regex will evaluate the corresponding template and write the result to ``stdout''.
-v string": If -v is specified, string will be used instead of ``stdin'' to match against patterns.

The argument pattern is a regular expression of the form described in regcmp(3G). 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 doesn't 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".

Examples

To cut the 4th through 8th letters out of a string (this example will output string).

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

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

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

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.''

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 '^([^:]*)$0.*$' '
   name=$m0
   action=`message "$m0 is a user"`'`

Diagnostics

If no patterns match, regex returns FALSE, otherwise regex returns TRUE.

Notices

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 on).

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.

References

awk(1), cut(1), grep(1), paste(1), regcmp(3G), sed(1)