open my $filehandle_txt, '<', $filepath_txt or die "cannot open '$filepath_txt': $!";

use strict; 
use warnings; 
require Image::ExifTool; 
 
for my $filepath_gif ( <*.gif> ) 
{ 
    my $filepath_txt = $filepath_gif . '.txt'; 
    my $filepath_xmp = $filepath_gif . '.xmp'; 
     
    open my $filehandle_txt, '<', $filepath_txt or die "cannot open '$filepath_txt': $!"; 
    my %hash = map { my$s=$_;$s=~s/[\s:]*$//;$s } grep /\S+/, <$filehandle_txt>; 
    close $filehandle_txt; 
     
    my $exifTool = new Image::ExifTool; 
    $exifTool->SetNewValue(Author => $hash{Title}) or die; 
    $exifTool->WriteInfo( undef, $filepath_xmp, 'XMP' ); 
}

perl test1.pl

ls -l 123.gif*

for my $filepath_gif ( <*.gif> )

for my $filepath_gif ( <*.gif.txt> )

my $filepath_txt = $filepath_gif . '.txt';  
say "File $filepath_txt does not exist" and next unless -f $filepath_txt ; 
# ...

cannot open '123.gif.txt.txt': No such file or directory at test2.pl line 10.

"my" variable $filepath_txt masks earlier declaration in same scope at test3.pl line 18. 
String found where operator expected at test3.pl line 19, near "say "File $filepath_txt does not exist"" 
	(Do you need to predeclare say?) 
syntax error at test3.pl line 19, near "say "File $filepath_txt does not exist"" 
Execution of test3.pl aborted due to compilation errors.

-rwxrwxrwx@ 1 Andi  staff  873930  4 Mar  2015 1425.gif  
-rwxrwxrwx@ 1 Andi  staff     614  4 Mar  2015 1425.gif.txt

#!/usr/bin/perl 
 
use strict; 
use warnings; 
use diagnostics; 
 
foreach my $file (<*.gif*>) { 
    print "$file\n"; 
}

#!/usr/bin/perl 
 
use strict; 
use warnings; 
use diagnostics; 
 
foreach my $file (<*.gif>) { 
    chomp $file;  # this isn't really needed but, 
                  # I put it in on the odd chance that 
                  # the diamand operator in the old perl 
                  # appended a line terminator to the filename 
     
    print "$file\n"; 
     
    my $txt_file = "$file.txt"; 
    if (-e $txt_file) { 
        print "$txt_file exists "; 
         
        if (-r $txt_file) { 
            print "and is readable\n"; 
        } 
        else { 
            print "BUT is NOT readable\n"; 
        } 
    } 
    else { 
        print "$txt_file does not exist\n"; 
    } 
     
}