Timothy Johnson wrote:
>
> Ok, I figured that much, but I guess my question is this: Is there a
> pressing need to scope a predefined variable like $_? How could this
> adversely affect a program? (I'm not trying to be a smart aleck, I really
> want to know)
>
Hi,
Sorry for such a short answer in my first post, but actually,
scoping is brand new to me, so I was shy of going into a lot
of details on the matter.
However, since the whole idea behind using local or my with variables
is to prevent a variable name from writing over the same variable
name elsewhere in the script, it makes even *more* sense to me to
use local with Perl's special variables; in that they are used frequently
throughout one's script, (with different values/purposes).
If $_ were a constant value like pi throughout a script, that would be
different. Then there would be no purpose in scoping it.
Since I couldn't understand Jeff's code, (no offense, I'm new), I
wrote a script to demonstrate how the value of $_ could get changed
unexpectedly. (It took me an hour, but I learned from it, heh).
# THE MAIN PROGRAM PRINTS AN ARRAY. HOWEVER IT ALSO CALLS
# A SUBROUTINE THAT CHECKS EACH ELEMENT FOR "b". IF "b" IS
# FOUND, IT SAVES IT IN A FILE. THE SUBROUTINE SHOULD BE
# HARMLESS, RIGHT?
use strict;
our @list = qw(a b c d);
foreach (@list) {
&check_b;
print $_, "\n";
}
sub check_b {
foreach (@list) {
#local $_;
$_ =~ s/b/bb/;
# SAVE TO FILE
}
}
As is, @list is printed incorrectly, but if you uncomment #local $_;,
it'll print as expected.
Bompa
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