PERL Beginners - question about ( () if () ) while ();

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question about ( () if () ) while ();

William M West

2004-08-03, 3:57 pm

$ perl -e ' $entry = "willy"; (print "1") if (/$entry/) while ($_ = "will");
print "0"'
syntax error at -e line 1, near ") while"
Execution of -e aborted due to compilation errors.

seperating the bits seems to work. it seems to break down when i want to
use the if statement in combination with the while.

using print to simulate return values.

perhaps i should abandon this idiom and use a normal

while () {
if () {

}
}

i am curious as to why this error crops up...

thanks,

willy
http://www.hackswell.com/corenth

Jeff 'Japhy' Pinyan

2004-08-03, 3:57 pm

On Aug 3, West, William M said:

>$ perl -e ' $entry = "willy"; (print "1") if (/$entry/) while ($_ = "will");
>print "0"'
>syntax error at -e line 1, near ") while"
>Execution of -e aborted due to compilation errors.

Check 'perldoc perlsyn'. It explains that the "statement modifiers",
things like '... if CONDITION' and '... while CONDITION' are only allowed
after *simple* statements -- what they really should say is "expressions".

You're allowed to write

print 1 if /willy/;

because 'print 1' is an expression. You can't write

print 1 if /willy/ while <FILE>;

because 'print 1 if /willy' is not an expression, it's a statement.

--
Jeff "japhy" Pinyan % How can we ever be the sold short or
RPI Acacia Brother #734 % the cheated, we who for every service
http://japhy.perlmonk.org/ % have long ago been overpaid?
http://www.perlmonks.org/ % -- Meister Eckhart

William M West

2004-08-03, 3:57 pm

>Check 'perldoc perlsyn'. It explains that the "statement modifiers",
>things like '... if CONDITION' and '... while CONDITION' are only allowed
>after *simple* statements -- what they really should say is "expressions".
>
>You're allowed to write
>
> print 1 if /willy/;
>
>because 'print 1' is an expression. You can't write
>
> print 1 if /willy/ while <FILE>;
>
>because 'print 1 if /willy' is not an expression, it's a statement.
>

well, this restriction has forced me to come up with:

perl -e ' $entry = "willy"; (print /$entry/) while ($_ = "wil"); print "0"'

in this test it ends up not getting to print "0", but with a match it works
great :) i can apply it properly now when substituting a filehandle for
the expression in the while.

thank you!

>--
>Jeff "japhy" Pinyan % How can we ever be the sold short or
>RPI Acacia Brother #734 % the cheated, we who for every service
>http://japhy.perlmonk.org/ % have long ago been overpaid?
>http://www.perlmonks.org/ % -- Meister Eckhart

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