what does $subdir = "$BASEDIR/$subdir" unless $subdir =~ m{^/}; do

richill has asked for the wisdom of the Perl Monks concerning the following question:

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Re: what does $subdir = "$BASEDIR/$subdir" unless $subdir =~ m{^/}; do by rafl (Friar) on Mar 18, 2006 at 12:02 UTC
`$subdir =~ m{^/};` [download] returns a true value if $subdir starts with a '/'. So the whole statement leaves $subdir as it is, if it already is an absolute path (starting with /) or it prepends a $BASEDIR and stores the result in $subdir again. Cheers, Flo	[reply] [d/l]
Re: what does $subdir = "$BASEDIR/$subdir" unless $subdir =~ m{^/}; do by davidrw (Prior) on Mar 18, 2006 at 13:31 UTC
Another (more robust, platform-indpendent) way would be to use File::Spec: `use File::Spec; $subdir = File::Spec->rel2abs($subdir, $BASEBIR);` [download] But anyways, your confusion may come from seeing `m{^/}` instead of `/^\//`, which are equivalent. See perlop and perldoc:perlre for the `m//` operator. It could also be written as `m#^/#` or `m!^/!` (or many others). But any way it's written, it is a regex that is checking for a leading slash -- i.e. if the path is absolute or not. IFF that fails (since "unless" reads as "if !") then it prepends a base directory to $subdir. So after that statement $subdir should be an absolute path if it wasn't already.	[reply] [d/l] [select]