from perldoc perlop
The null filehandle <> is special: it can be used to emulate the
behavior of sed and awk.
Input from <> comes either from standard input, or from each file listed
on the command line.
Here's how it works: the first time <> is evaluated, the @ARGV array is
checked, and if it is
empty, $ARGV[0] is set to "-", which when opened gives you standard
input. The @ARGV array is
then processed as a list of filenames. The loop
while (<>) {
... # code for each line
}
is equivalent to the following Perl-like pseudo code:
unshift(@ARGV, '-') unless @ARGV;
while ($ARGV = shift) {
open(ARGV, $ARGV);
while (<ARGV>) {
... # code for each line
}
}
except that it isn't so cumbersome to say, and will actually work. It
really does shift the
@ARGV array and put the current filename into the $ARGV variable. It
also uses filehandle ARGV
internally--<> is just a synonym for <ARGV>, which is magical. (The
pseudo code above doesn't
work because it treats <ARGV> as non-magical.)
You can modify @ARGV before the first <> as long as the array ends up
containing the list of
filenames you really want. Line numbers ($.) continue as though the
input were one big happy
file. See the example in "eof" in perlfunc for how to reset line
numbers on each file.
On Wed, Feb 01, 2006 at 01:39:06PM -0800, Stephen A. Jarjoura wrote:
> Hello, all;
>
> I am debugging code written by someone else, and noticed the following:
> ===START=CODE===
> sub getParameters {
> my $parm_list = do { local(@ARGV,$/); <> };
> }
> ===END=CODE===
>
> This does what the author expected (slurp STDIN into the scalar "$parm_list")
> but I was surprised by the "<>" as a stand-in for <STDIN> so I looked it up.
> Here is what I found:
> http://perldoc.perl.org/perlvar.html
> ===START=PASTE===
> ARGV
>
> The special filehandle that iterates over command-line filenames in @ARGV .
> Usually written as the null filehandle in the angle operator <> . Note that
> currently ARGV only has its magical effect within the <> operator; elsewhere
> it is just a plain filehandle corresponding to the last file opened by <> .
> In particular, passing \*ARGV as a parameter to a function that expects a
> filehandle may not cause your function to automatically read the contents of
> all the files in @ARGV .
>
> $ARGV
>
> contains the name of the current file when reading from <>.
> ===END=PASTE===
>
> I could find no reference to "<>" as a synonym for "<STDIN>" ... am I missing
> something obvious? [The code works, so obviously it is my knowledge that is
> faulty.] If someone could point me at a reference or doc or faq, I'd be
> grateful.
>
> Also, is there any particular reason (in the example given above) why '@ARGV'
> would need to be localized, or is the author just being overly cautous?
>
> Thanks, in advance, for your input!
>
> ---
> Stephen ~runester~ Jarjoura
> http://runester.com
> http://boston.pm.org/kwiki/index.cgi?StephenJarjoura
>
>
>
> _______________________________________________
> Boston-pm mailing list
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> http://mail.pm.org/mailman/listinfo/boston-pm
>
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