open(my $fh, "<", $file) or die("file open failed for '$file': $!");

##</code><code>##

X:\>perl -e "open($file) || die('file open failed');"
file open failed at -e line 1.

X:\>perl -e "open('xx') || die('file open failed');"
file open failed at -e line 1.

##</code><code>##

perl -e "$FILE='file_that_exists';open(FILE) || die('file open failed');"

##</code><code>##

X:\>perl -w tmp.pl
Name "main::IN" used only once: possible typo at tmp.pl line 5.
Couldn't open `/tmp/test123' at tmp.pl line 5.

X:\>type tmp.pl
use strict;
sub push_report {
    my $idx = shift;
    my $file= "/tmp/test123";
    open(IN, $file) || die "Couldn't open `$file'";
}

##</code><code>##

use strict;
sub push_report {
    my $idx = shift;
    my $file= "/tmp/test123";
    if (-e $file) {
        warn "'$file' exists";
    } else {
        warn "'$file' does not exist";
    };
    if (-f $file) {
        warn "'$file' exists as a file";
    };
    if (-d $file) {
        warn "'$file' exists as a directory";
    };
    open(IN, $file) || die "Couldn't open `$file'";
}