Personally I write your code like this:

use English '-no_match_vars';
open $input_fh, '<', $input_fn or die 'Could not open file: ', $OS_ERR
+OR;
my $hash;
while ( my $line = <$input_fh> ) {

    chomp $line;
    
    last if ! $line;
    
    # Split line with a limit of two
    my ( $word1 , $word2 ) = split /:/, $line, 2;  
    $hash->{$word1} = $word2;   
}
close $input_fh or die 'Could not close file: $OS_ERROR';
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Alot of coding practices are personal preference but there are some good guidelines to follow.
I would say always use lexical variable for file handles. You can assign a lexical fh by opening as i've done or by using the glob from the symbol table like this:

my $output = *STDOUT;
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Then you can even pass it via subroutines to assign handles:

## This in a package else where
## 'inside-out obj'
sub assign_log_handle {
   my $self = shift;
   $log_handle->{$self} = shift;
   return;
}

## From main code
Your::Package->assign_log_handle( *STDERR );
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Update: Just seen ikegami has already got there with this, But oh well. note: $OS_ERROR is the same as the $! that he mentioned.
Update: added: '-no_match_vars' :P John