Format string and regex question

r.joseph has asked for the wisdom of the Perl Monks concerning the following question:

I have a program which returns data formatted according to a format string that will be entered by the user. Lets say the string looks like this:

%a-%b-%c: %x.%y.%z

What I want is simply to have the letters replaced with local (my()-declared vars in a sub) varibles and then simply output. This is what I was using, but returns oddly-formatted string:

sub foo {
   my $format_string = shift;
   my $a = ...;
   my $b = ...;
   ...
   my $z = ...;

   $format_string =~ s/(%(\w))/eval "$$2"/e;
   return $format_string;
}
[download]

but that never works...it returns different things at different times, but it never replaces all the varibles across the string. What am I doing wrong?

Thanks to all and happy 19001!!

R.Joseph

Comment on Format string and regex question Download Code

Replies are listed 'Best First'.
Re: Format string and regex question by Fastolfe (Vicar) on Jan 01, 2001 at 21:27 UTC
You may be better off puting this data into a hash instead of using eval like this. `sub foo { my $format_string = shift; my %vars = ( a => ..., b => ..., c => ..., ); $format_string =~ s/(%(\w))/$vars{$1}/eg; return $format_string; }` [download] That keeps the users out of your name space entirely, and drops the reliance on the 'eval'. This should be tons more efficient for you.	[reply] [d/l]
Re: Format string and regex question by dws (Chancellor) on Jan 01, 2001 at 15:36 UTC
Without the `/g` (global) modifier, the subsitution only fires once. Try $format_string =~ s/%(\w)/eval "$$1"/ge;	[reply] [d/l]
Re: Re: Format string and regex question by repson (Chaplain) on Jan 01, 2001 at 16:04 UTC
Just one slight problem... `$$` is the current program pid, since $1 is not a scalar ref to dereference. It might be better to quote the first $ sign if this behaviour is not desireable (which would have been the cause for half of the original problem as well). `$format_string =~ s/%(\w)/"\$$1"/eeg;` And the second eval can be moved outside.	[reply] [d/l] [select]
Re: Format string and regex question by I0 (Priest) on Jan 01, 2001 at 20:06 UTC
A third problem is that your `my` variables are not in the scope of your `eval`.	[reply] [d/l] [select]