note rjt <p>Good replies so far, so I won't steal anyone's monastic thunder, although I'll add that Perls >= 5.10 have the [doc://perlop#Logical-Defined-Or|logical defined-or operator], <c>//</c>. Often this is what you really want, but since there is a lot of code in the wild that pre-dates it, you may notice disproportionate use of <c>||</c>.</p> <p>The difference is simple:</p> <ol> <li>Use <c>$a //= 'foo';</c> when you want to assign 'foo' to $a if $a is not [doc://defined].</li> <li>Use <c>$a ||= 'foo';</c> when you want to assign 'foo' to $a if $a has a false value, such as zero or an empty string.</li> </ol> 1004257 1004257