2014-02-17T11:54:00 Muffi

while ( my $line = <STDIN> ) {  suggeriert beim Lesen eine Abbruchbedingung, ist aber keine. Dann würd ich das auch klar machen.

perlop

perldoc perlop

...
The following lines are equivalent:

Code (perl): (dl )

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    while (defined($_ = <STDIN>)) { print; }
    while ($_ = <STDIN>) { print; }
    while (<STDIN>) { print; }
    for (;<STDIN>;) { print; }
    print while defined($_ = <STDIN>);
    print while ($_ = <STDIN>);
    print while <STDIN>;

This also behaves similarly, but assigns to a lexical variable instead of to $_ :

Code (perl): (dl )

    while (my $line = <STDIN>) { print $line }

In these loop constructs, the assigned value (whether assignment is automatic or explicit) is then tested to see whether it is defined. The defined test avoids problems where the line has a string value that would be treated as false by Perl; for example a "" or a "0" with no trailing newline. If you really mean for such values to terminate the loop, they should be tested for explicitly:

Code (perl): (dl )

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    while (($_ = <STDIN>) ne '0') { ... }
    while (<STDIN>) { last unless $_; ... }

In other boolean contexts, <FILEHANDLE> without an explicit defined test or comparison elicits a warning if the use warnings pragma or the -w command-line switch (the $^W variable) is in effect.