doesn't mention an important special-case about glob references/ <>,
perl -e 'my $fh; open($fh, "<", "/etc/services"); print <$fh>, "\n";'
versus
perl -e 'my $fh; open($fh, "<", "/etc/services"); print <{$fh}>, "\n";'
Or print <${fh}>
It would have been a kindness to explain the problem for those of us
who were unfamiliar with it. It took me a little while to find the
explanation.
"man perlop", towards the end of the I/O Operators section (in the
Perl version I checked):
If what the angle brackets contain is a simple scalar variable
(e.g., <$foo>), then that variable contains the name of the
filehandle to input from, or its typeglob, or a reference to
the same. For example:
$fh = \*STDIN;
$line = <$fh>;
If what's within the angle brackets is neither a filehandle nor
a simple scalar variable containing a filehandle name,
typeglob, or typeglob reference, it is interpreted as a
filename pattern to be globbed, and either a list of filenames
or the next filename in the list is returned, depending on
context. This distinction is determined on syntactic grounds
alone. That means "<$x>" is always a readline() from an
indirect handle, but "<$hash{key}>" is always a glob(). That's
because $x is a simple scalar variable, but $hash{key} is
not--it's a hash element. Even "<$x >" (note the extra space)
is treated as "glob("$x ")", not "readline($x)".
One level of double-quote interpretation is done first, but you
can't say "<$foo>" because that's an indirect filehandle as
explained in the previous paragraph. (In older versions of
Perl, programmers would insert curly brackets to force
interpretation as a filename glob: "<${foo}>". These days,
it's considered cleaner to call the internal function directly
as "glob($foo)", which is probably the right way to have done
it in the first place.)
So on this system,
perl -e 'my $fh; open($fh, "<", "/etc/services"); print <$fh>, "\n";'
outputs the contents of the file /etc/services, but
perl -e 'my $fh; open($fh, "<", "/etc/services"); print <{$fh}>, "\n";'
outputs one line,
GLOB(0xbb5061d0)
I didn't know that. Thank you.
.