### RE: Double Interpolation of a String

by davorg (Chancellor)
 on Jun 22, 2000 at 14:30 UTC ( #19415=note: print w/replies, xml ) Need Help??

in reply to Double Interpolation of a String

For doing stuff with these kinds of substitutions, I always use code like this:

```use strict;

my %trans = (color => 'red',
fruit => 'apple',
name => 'chromatic');

my \$string = 'Hi, my name is \$name.  Please hand me a \$color \$fruit.';

\$string =~ s/\\$(\w+)/\$trans{\$1}/eg;

print \$string;

--
<http://www.dave.org.uk>

European Perl Conference - Sept 22/24 2000
<http://www.yapc.org/Europe/>

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Infinite Recursion of a String
by tadman (Prior) on Feb 07, 2001 at 00:30 UTC
With inspiration from davorg's above example, taking it a step further (and a step further (and a step further (...))):
```     #!/usr/bin/perl -w

use strict;

my %trans = (
'\$name'  => 'Frank',
'\$color' => 'Cherry Red',
'\$time'  => sprintf ("%d:%02d:%02d",
(localtime(time))[2,1,0]),
'\$date'  => sprintf ("%04d-%02d-%02d",
(localtime(time))[5] + 1900,
(localtime(time))[4] + 1,
(localtime(time))[3]),
'\$dstr'  => '\$time on \$date',
);

my (\$trans_rx) = join ('|', sort { length(\$b) - length(\$a) }
sort
map { quotemeta (\$_) }
keys %trans);

my (\$string) = 'I\'m \$name and I prefer \$color objects, at least
+on \$dstr';

while (\$string =~ s!(\$trans_rx)!\$trans{\$1}!o) { }

print "\$string\n";
For output like:
```     I'm Frank and I prefer Cherry Red objects, at least on 15:33:43 o
+n 2001-02-06
This version doesn't replace stray references to things like \$1.95 with nothing, but it might get caught in a loop if you specify two entries which convert to eachother recursively such that "\$a -> \$b" and "\$b -> \$a".
It might be useful to protect against infinite recursion as well:
```my \$max_recurs = 10;
\$max_recurs-- while \$string =~ ... && \$max_recurs;

warn "Too many recursive substitutions on '\$string'"
if !\$max_recurs && \$^W;

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