I defined it like this:

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

open (DATA, "dic") || die "Error opening the input file\n"; 
print "Reading mapping file\n";
print "----------------------------\n";
    
open (INFILE, "trial.txt") || die "Error opening the input file\n"; 
print "Reading input file\n";
print "----------------------------\n";

my %dict;

while (my $line = <INFILE>) {
my $old_string = $line;
while ( <DATA> ) {
    my ( $key, $val ) = /^(\d+)\s+(\w+)/;
    $dict{ $val } = $key;
    }

my $cc = join '', keys %dict;
my ( $min ) = my ( $max ) = map length, keys %dict;
for ( map length, keys %dict ) {
    $min = $_ if $min > $_;
    $max = $_ if $max < $_;
    }

my $pattern = qr/\b([$cc]{$min,$max})\b/;

( my $new_string = $old_string ) =~ s/$pattern/ exists $dict{ $1 } ? $
+dict{ $1 } : $1 /eg;
print "$new_string\n";

}
close (INFILE);
close (DATA);
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but I get this error:

Reading mapping file
----------------------------
Reading input file
----------------------------
april 1168 0.06781456

Use of uninitialized value in concatenation (.) or string at seek.pl l
+ine 29, <DATA> line 19969.
Use of uninitialized value in concatenation (.) or string at seek.pl l
+ine 29, <DATA> line 19969.
Unmatched [ in regex; marked by <-- HERE in m/\b([ <-- HERE ]{,})\b/ a
+t seek.pl line 29, <DATA> line 19969.
[download]

Not that 19969 is my last line in dictionary file. and also how can I ignore the cases in matching? for example in dictionary file April exists but april does not, so I tend to make it case insensetive. thanks in advance.