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6.9. Matching Shell Globs as Regular Expressions
6.9.1. Problem
You want to
allow users to specify matches using traditional shell wildcards, not
full Perl regular expressions. Wildcards are easier to type than full
regular expressions for simple cases.
6.9.2. Solution
Use the following subroutine to convert four shell wildcard
characters into their equivalent regular expression; all other
characters are quoted to render them literals.sub glob2pat {
my $globstr = shift;
my %patmap = (
'*' => '.*',
'?' => '.',
'[' => '[',
']' => ']',
);
$globstr =~ s{(.)} { $patmap{$1} || "\Q$1" }ge;
return '^' . $globstr . '$';
}
6.9.3. Discussion
A Perl regex pattern is not the same as a shell wildcard pattern. The
shell's *.* is not a valid regular expression. Its
meaning as a pattern would be /^.*\..*$/s, which
is admittedly much less fun to type.The function given in the Solution makes these conversions for you,
following the standard wildcard rules used by the
glob built-in. Table 6-2 shows
equivalent wildcard patterns in the shell and in Perl.
Table 6-2. Shell globs and equivalent Perl wildcard patterns
Shell | Perl |
|---|---|
list.? | ^list\..$ |
project.* | ^project\..*$ |
*old | ^.*old$ |
type*.[ch] | ^type.*\.[ch]$ |
*.* | ^.*\..*$ |
* | ^.*$ |
would lock in (and out) any modifier flags, such as
/i, but we'd rather delay that decision until
later.Shell wildcard rules are different from those of a regular
expression. The entire pattern is implicitly anchored at the ends; a
question mark maps into any character; an asterisk is any amount of
anything; and brackets are character ranges. Everything else is a
literal.Most shells do more than simple one-directory globbing. For instance,
*/* means "all files (including directory files)
in all subdirectories of the current directory." Also, shells usually
don't expand wildcards to include files with names beginning with a
period; you usually have to put that leading period into your glob
pattern explicitly. Our glob2pat function doesn't
do these things—if you need them, use the File::KGlob module
from CPAN.
6.9.4. See Also
Your system manpages for the various shells, such as
csh(1), tcsh(1),
sh(1), ksh(1), and
bash(1); the glob function in
perlfunc(1) and Chapter 29 of
Programming Perl; the documentation for the
CPAN module Glob::DosGlob; the "I/O Operators" section of
perlop(1); we talk more about globbing in Recipe 9.6
|  | |
| 6.8. Extracting a Range of Lines |  | 6.10. Speeding Up Interpolated Matches |
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