my $tool_name = "tar";  # simple example
my $tool_path = '';

for my $path ( split /:/, $ENV{PATH} ) {
    if ( -f "$path/$tool_name" && -x _ ) {
        print "$tool_name found in $path\n";
        $tool_path = "$path/$tool_name";
        last;
    }
}
die "No $tool_name command available\n" unless ( $tool_path );

##</code><code>##

my $tool_name = "tar";
my $tool_path = `which $tool_name`;
die "No $tool_name command available\n" unless ( $tool_path );