String interpolation

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

Hi all,

I have a string defined as follows:

my $str = 'params.$idx.arg';
[download]

$idx will be assigned with integer values in a loop as follows:

for my $idx (0..10) {
    &do_something($str);
}
[download]

The thing is that I want $str in the loop to be interpulated with the value of $idx in each loop iteration (the above code will not take there of course), meaning do_something() will get a different parameter each loop iteration ('params.0.arg', 'params.1.arg', etc.).
How can I achive that?

Thanks

Retitled by davido: Corrected spelling of 'interpolation' to improve searchability.

Hotshot

Comment on String interpolation Select or Download Code

Replies are listed 'Best First'.
Re: String interpolation by fglock (Vicar) on Dec 09, 2004 at 13:03 UTC
`use strict; my $str = sub { "params.$_[0].arg" }; sub do_something { print +shift, "\n" } for my $idx (0..10) { do_something( $str->($idx) ); }` [download] output: `params.0.arg params.1.arg params.2.arg params.3.arg params.4.arg params.5.arg params.6.arg params.7.arg params.8.arg params.9.arg params.10.arg` [download]	[reply] [d/l] [select]
Re: String interpolation by gellyfish (Monsignor) on Dec 09, 2004 at 13:19 UTC
An alternative to the other suggestions is to use `(s)printf`: `my $str = 'params.%d.arg'; + for my $idx (0 .. 9 ) { printf $str, $idx; }` [download] You will need to be careful in sanitizing the contents of `$str` if all or part of it is being taken from user (or otherwise untrusted) input . /J\	[reply] [d/l] [select]
Re: String interpolation by reneeb (Chaplain) on Dec 09, 2004 at 12:56 UTC
use " instead of ': `my $str = "params.$idx.arg";` That means for your code: `for(0..10){ my $str = "params.$idx.arg"; do_something($str); }` [download]	[reply] [d/l] [select]
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Re: String interpolation by edan (Curate) on Dec 09, 2004 at 13:09 UTC
I think the easiest solution is using the dreaded string eval: `for my $idx (0..10) { my $interp_str; eval "\$interp_str = qq($str)"; do_something($interp_str); }` [download] All the usual caveats about untainting user inputs apply, of course. -- edan	[reply] [d/l]
Re: String interpolation by kelan (Deacon) on Dec 09, 2004 at 13:24 UTC
Do your own interpolation: `for my $idx ( 0 .. 10 ) { my $newstr = $str; $newstr =~ s/\$idx/$idx/; do_something( $newstr ); }` [download]	[reply] [d/l]
Re: String interpolation by kappa (Chaplain) on Dec 09, 2004 at 15:19 UTC
That's eval thing. `#! /usr/bin/perl -w use strict; my $str = '"number $idx\n"'; foreach my $idx (1 .. 10) { print eval($str); }` [download] --kap	[reply] [d/l]
Re: String interpolation by hotshot (Prior) on Dec 09, 2004 at 15:02 UTC
Thanks guys, but fglock's solution is the best for me, I wanted to avoid using additional temporary parameters (I already knew these options), but thanks anyway. Hotshot	[reply]


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