Re^2: Modification of a read-only value

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Re^3: Modification of a read-only value by Aristotle (Chancellor) on Aug 21, 2004 at 16:10 UTC
`:)` I first saw this in a question in the monastery a long time ago. That was a far nastier case, though: someone was getting spurious action at a distance. Turns out one of his map blocks was calling a sub containing a `while(<FH>)`, and because map aliases `$_`, the function modified the values in his source array. Ouch. Ever since, `while(<FH>)` used without a local has been a red flag in my mind. Always localize `$_` when you use this construct. (Or use a different variable, as you did, of course.) Makeshifts last the longest.	[reply]
Re^3: Modification of a read-only value by ikegami (Patriarch) on Aug 22, 2004 at 01:36 UTC
`while (<PIPE>)` is equivalent to `while (defined($_ = <PIPE>))` so you might want to use `while (defined($foo = <PIPE>))` instead of `while ($foo = <PIPE>)` What you are using will stop when you don't expect it (such as when you read in a blank line).	[reply] [d/l] [select]
Re^4: Modification of a read-only value by Aristotle (Chancellor) on Aug 22, 2004 at 09:28 UTC
Perl's one step ahead of you: `$ perl -MO=Deparse -e'while($foo=<>){}' while (defined($foo = <ARGV>)) { (); } -e syntax OK` [download] This is a relatively recent change from two or so years ago, though; I don't rememeber which version introduced it off-hand. Even without the definedness test it wouldn't stop on a blank line either, btw. Don't forget the record separator. A blank line is not an empty string; it's `"\n"`. What that construct would fail to process is the very last line of a file, if it contains only a `0` and is not terminated by a record separator. (It can't be blank, obviously, because a blank line with no record separator is, well, err, no line at all. `:-)`) Makeshifts last the longest.	[reply] [d/l]