Why isn't my octal data interpreted correctly?

Perl only understands octal and hex numbers as such when they occur as literals in your program. If they are read in from somewhere and assigned, no automatic conversion takes place. You must explicitly use oct or hex if you want the values converted. oct interprets both hex (``0x350'') numbers and octal ones (``0350'' or even without the leading ``0'', like ``377''), while hex only converts hexadecimal ones, with or without a leading ``0x'', like ``0x255'', ``3A'', ``ff'', or ``deadbeef''.

This problem shows up most often when people try using chmod, mkdir, umask, or sysopen, which all want real permissions in octal. 

    chmod(644,  $file);	# WRONG -- perl -w catches this
    chmod(0644, $file);	# right