my @records = split(/^(?=I)/m, $file);
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The just extract the REFDES and modify the PKG_TYPE

my %pkg_lkup (
   ... => ...,
   ... => ...,
   ... => ...,
);

for my $rec (@records) {
   if ( my ($refdes) = $rec =~ /REFDES=(.*)/ ) {
      if (exists($pkg_lkup{$refdes})) {
         $rec =~ s/PKG_TYPE=.*/PKG_TYPE=$pkg_lkup{$refdes}/;
      }
   }
   print($rec);
}
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In Perl 5.10, the substitution can be written more efficiently as

$rec =~ s/PKG_TYPE=\K.*/$pkg_lkup{$refdes}/;
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OK I think I understand this all for the most part, I've been working on files on a line by line basis for so long I didn't think I could break it up any other way. But of course something I imagine is pretty simple has got me stuck.

How do I get the entire content of a file into $file? I know how to read a file into @file, but I'm at a loss how to read the whole thing into $file to then split it up.

The canonical solution is:

my $file = do {
   local $/;
   <>;
};
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But, we're in Perl, so there's more than one way to do it.

  $file = join( '', <> );
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also works. Of course, you could look at File::Slurp for a CPAN-based solution that's a little more readable.

PS. if you have an open filehandle in $fh, you would replace <> with <$fh> in the above, of course.

G. Wade

#!/usr/bin/perl --
use strict;
use warnings;

die "Usage: $0 filetoprocess\n" unless @ARGV;

my %subst = 
  ('C25' => 'SMS0011',
   'U23' => 'TQF0022',
# ...
   'U25' => 'TQF1223',
   );


$/ = "\nI ";                    # use own input record separator

while (<>) {                    # read a record and substitute if a ma
+tch found
    if (my ($rd) = /REFDES=(\w+)/) {    
        s/PKG_TYPE=(\w+)/PKG_TYPE=$subst{$rd}/ if exists $subst{$rd};
    }
    print;
}
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