http://www.perlmonks.org?node_id=494485

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

Hi all,

Is it possible to have a ternary expression within the replacement bit of the regular expression? I've the following code and I'm trying to fix the size of font (captured in $1) if it's greater than 5: 

$message =~ s~\[size=(.+?)\](.+?)\[/size\]~'<font size="' . $1 .  '">'
+ . "$2</font>"~eisg;

# I'm trying to test $1 so that if it's greater than 5,
# fix it at 5, else leave it unchanged.

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Thanks in advance :)

Replies are listed 'Best First'.
Re: Ternary inside a regex
by izut (Chaplain) on Sep 23, 2005 at 12:17 UTC
    You can do that using the /e modifier: 
    $a = "size=1111"; 
$a =~ s/(\d+)/($1 > 5) ? 5 : $1/e; 
print $a, "\n"

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    Igor S. Lopes - izut
    surrender to perl. your code, your rules.
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      Thanks, izut!

      Changed my code to the following and it works: 

      $message =~ s~\[size=(.+?)\](.+?)\[/size\]~($1 > 5) ? "<font size=\"5\
+">$2</font>" : "<font size=\"$1\">$2</font>"~eisg;

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        I think this way is easier to read: 
        message =~ s~\[size=(.+?)\](.+?)\[/size\]~"<font size=\"".(($1 > 5) ? 
+5 : $1)."\>$2</font>"~eisg;

        [download]

        Igor S. Lopes - izut
        surrender to perl. your code, your rules.
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Re: Ternary inside a regex
by blazar (Canon) on Sep 23, 2005 at 15:04 UTC
    You're already using the /e modifier. Thus you can put into the replacement portion of the s/// operator "any" perl code. No reason why a ternary operator could not be there...
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Re: Ternary inside a regex
by ww (Archbishop) on Sep 24, 2005 at 10:45 UTC
    At worst, another way with the ternary (or "conditional") operator: 
    use vars qw ( $message);

$message = qq ( Foo bar <font size="7"> phrase here </font> blivits. )
+;

$message =~ s#(\d+)#($1 > 5) ? 5 : $1#eisg;

if ( $1 ) {
         print "\n After s###, \$1 is: $1 \n ...and revised \$msg is: 
+$message \n";
        }
         else 
        {
         print "\n no \$1 found \n";
}

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    and output is:
    After s###, $1 is: 7
    ...and revised $message is: Foo bar <font size="5"> phrase here </font> blivits.
    • the $message html fragment is well-formatted... for 4.0, but display elements are now better (well, that's what the experts say) done with css
    • the "sig" regex modifiers are not needed with this $message but might well be with more typical .html
    • and, while matching on <font size=" before the 7> is omitted only to keep the example simple (and is easy enough to add), this is a very limited and profoundly un-extensible method -- better to use an html parser, as suggested elsewhere. For example, a web'ster using <font... may well have multiple and/or variant forms of elements in a single font tag, as, for example,
      <font color="red" size=+1...>
    • and, finally, despite generous efforts by OP, I can't see how Re^2 or Re^3 can or do work ... even with "<"s replacing "["s
      ...so would welcome education.
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