Does while localize $

Your comment and several others I have seen here suggest that while(FH) and foreach automatically localize $_. But the folowing code seems does not revert to the old $_ after leaving the while loop. What am I missing? Thanks.

use strict; use diagnostics;
$_ = "Before";
print "Before loop= $_\n";
while (<>){
    print "In while loop= $_\n";
    last;
}
print "After while loop= $_\n";

Output:
Before loop= Before
myinput  (entered from the keyboard)
In while loop= myinput

After while loop= myinput
[download]

Comment on Does while localize $_? Download Code

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Re: Does while localize $_? by danger (Priest) on Mar 19, 2001 at 00:07 UTC
A foreach loop does implicitly localize $_ (or whatever variable is being used as the loop variable), but $_ is not automatically localized for `while(<>)` loops. Here is the relevant entry from the perlop manpage: Ordinarily you must assign the returned value to a vari- able, but there is one situation where an automatic assignment happens. If and only if the input symbol is the only thing inside the conditional of a `while' state- ment (even if disguised as a `for(;;)' loop), the value is automatically assigned to the global variable $_, destroy- ing whatever was there previously. (This may seem like an odd thing to you, but you'll use the construct in almost every Perl script you write.) The $_ variables is not implicitly localized. You'll have to put a `local $_;' before the loop if you want that to happen. However, that last line is misleading: you'll need to wrap it all in a block, or localize $_ in the while condition to get the proper effect: `{ local $_; while(<>){ print; } } # or, while(local $_ = <>) { print; }` [download]	[reply] [d/l] [select]
Re: Does while localize $_? by merlyn (Sage) on Mar 19, 2001 at 00:07 UTC
No, while doesn't use automatic localizing. Foreach does. -- Randal L. Schwartz, Perl hacker	[reply]
Re: Re: Does while localize $_? by tenya (Beadle) on May 25, 2001 at 07:46 UTC
Which is helpful because this allows while loops inside the foreach loop to use the foreach $_. Correct?	[reply]


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Does while localize $_?