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Thanks! Learn something every day! (well, lots today). But what is going on here? What (under the covers) makes this a special case? Why is Perl wrapping $_=<> in defined($_ =<>)? Another convenience feature? And where else does this happen?

Here's my output with a slightly expanded print line checking both the value and the defined status and just to make sure there was no monkey business with the special variable $_ I changed it to $line - same result as you, of course. (I had to switch " and ' to keep the bash shell from trying to resolve $_):

$ perl -e'print 0' | perl -e'while ($line = <>) { print "\$line=<$lin +e> \$line=<" . ($line ? "true" : "false") . "> defined=<" . (defined( +$line) ? "true" : "false") . ">\n"};' $line=<0> $line=<false> defined=<true>

It is also not anything special about the syntax $somevar = <> because I get the same result if I use readline(...):

$ perl -e'print 0' | perl -e'while ($line = readline(*STDIN)) { print +"\$line=<$line> \$line=<" . ($line ? "true" : "false") . "> defined=< +" . (defined($line) ? "true" : "false") . ">\n"};' $line=<0> $line=<false> defined=<true>

Or is it? Could it be that both while($somevar = readline(...)) and while($somevar = <...>), but only these, have special semantics? I noticed that if I wrap readline in a function of my own that the special behavior goes away. For example,

use strict; use warnings; #The following all output: # BEFORE # $line=<0> $line=<false> defined=<true> # AFTER # # while (my $line = readline(*STDIN)) { # while (my $line = <STDIN>) { # while (my $line = <>) { # # but wrapping readline in a sub produces only # BEFORE # AFTER print "BEFORE\n"; while (my $line = wrapped_readline(\*STDIN)) { print "\$line=<$line> \$line=<" . ($line ? "true" : "false") . "> defined=<" . (defined($line) ? "true" : "false") . ">\n"; } print "AFTER\n"; sub wrapped_readline { my $fh = shift @_; my $sLine = readline($$fh); #print "wrapped_readline: <$sLine>\n"; return $sLine; }

Thanks in advance, beth

Update: refined question a bit; fixed error in sub of $_ with $line; added examples using readline and a sub wrapping readline.


In reply to Re^3: "defined" in while loop Edit | Delete | Quote | Reply | Private Reply by ELISHEVA
in thread "defined" in while loop Edit | Delete | Quote | Reply | Private Reply by manish.rathi

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