How do pack a regular expression in a variable?

pppaulll has asked for the wisdom of the Perl Monks concerning the following question:

I'm trying to read regular expressions from a parameter file. This works as long as I specify the outer delimiters around the variable in the code. I include the delimiters in the variable, otherwise I have no way of allowing users to generate expressions that use external modifiers like:

    /coWs/i
[download]

The parameter file (following) uses the first character to specify what operation (search or exception) the user wants to perform. The regexp runs from column 2 to the end of the line. What I want to do is use delimiters and modifiers included in the parameter file:

    +/six/i
    -/were/
[download]

This works when delimiters are not included in the parameter file, but is very limited and flakey.

    +[Ss][Ii][Xx]
[download]

Here is some of the code:


# Process Global Exceptions first

foreach $except (@$glob_except) {
    $cexcept = substr($except, 1);
    $targf{$tkey} = "1:0" if ($tkey =~ /$cexcept/);  # EXPANDS VARIABL
+E HERE

### I would like the delimeters to be contained in the variable:  ...(
+$tkey =~ $cexcept);

}

elsif ($ttype eq '+') {
    if ($tkey =~ /$ttext/) { ;  # EXPANDS VARIABLE HERE
        $targf{$tkey} = "3:$err_rtn";
        $found = 1;
    }
}
elsif ($ttype eq '-' && substr($targf{$tkey},0,1) == 3) {
    if ($tkey =~ /$ttext/) {;  # EXPANDS VARIABLE HERE
        $targf{$tkey} = "2:0";
        $found = 0;
    }
}
else {
### ETCETERA     

### THIS IS HOW THE HASH CONTAINING THE MATCH STRING IS LOADED

elsif ($line_header eq '!') { ## Optional
# Spec a global exception that affects all lines
# interpolation takes place. 
unless ($trans_state == 2) 
    {die "ERR: Global exception out of sequence";}
    push (@$glob_except, $line);    #  &lt;= LOADING THE VARIABLE FROM
+ FILE
    # Trans state stays at 2 until set to 3 in subsequent logic
[download]

Comment on How do pack a regular expression in a variable? Select or Download Code

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Re: How do pack a regular expression in a variable? by japhy (Canon) on Nov 29, 2001 at 21:45 UTC
You want to use `eval()`, I'd say. This is almost exactly a section of my book that I wrote last night! `open REs, "< re_file" or die "can't read re_file: $!"; while (<REs>) { chomp; my $mode = substr($_, 0, 1, ''); # reverse-chop push @re, [ $mode, match_maker($_) ]; } close REs; # make me a match... ;) sub match_maker { my $pat = shift; return eval qq{ sub { \$_[0] =~ $pat } }; }` [download] If you call `match_maker($foo)`, and `$foo` is `'/age:\s(\d+)/i'`, then the resulting function returned behaves exactly* like: sub { $_[0] =~ */age:\s(\d+)/i** } Now you have an array, `@re`, with array references holding the mode ('+' or '-') and a function you can run to match against a string. `for (@re) { my ($mode, $func) = @$_; if ($func->($string)) { # this is your pattern match! if ($mode eq '+') { print "this is ok\n"; } else { print "this matched an exception\n"; } } }` [download] _____________________________________________________ Jeff`[japhy]`Pinyan: Perl, regex, and perl hacker. `s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;`	[reply] [d/l] [select]
Re: How do pack a regular expression in a variable? by davorg (Chancellor) on Nov 29, 2001 at 22:37 UTC
Perhaps you need to include your options within the regular expression. For example: `/(?i)foo/` [download] is equivalent to `/foo/i` [download] You can then leave the delimiters off and just put `(?i)foo` in your configuration file. See "Cloistered Pattern Modifiers" on p186 of the Camel (3ed) or the perlre section on `(?imsx-imsx)` for more details. -- <http://www.dave.org.uk> "The first rule of Perl club is you don't talk about Perl club."	[reply] [d/l] [select]
Answer: How do pack a regular expression in a variable? by Anonymous Monk on Nov 30, 2001 at 20:14 UTC
I came up with something that seems to work - using an eval to evaluate a string containing the regular expression variable... `FEOUTER: while ($tkey = each(%targf)) { # Apply Search and Exception to each log line $found = 0; foreach $scline (@$srch_except) { # Split string intonext FEOUTER; qualifier and text $ttype = substr($scline, 0, 1); $ttext = substr($scline, 1); $eval_cd = "\"$tkey\" =~ $ttext"; if ($ttype eq '!') { if (eval "$eval_cd") { $targf{$tkey} = "1:0"; next FEOUTER; } } elsif ($ttype eq '&') {` [download]	[reply] [d/l]