They're not 100% identical, as the following code shows:
use warnings;
use FileHandle;
$fh = new FileHandle "file", "r";
if (defined $fh) {
print <$fh>;
undef $fh; # automatically closes the file
}
$fh2 = new FileHandle "file", "r";
if (defined $fh2) {
print <$fh2>;
close $fh2; # automatically closes the file
}
print <$fh>;
print <$fh2>;
Output:
Use of uninitialized value in <HANDLE> at t line 16.
readline() on unopened filehandle at t line 16.
readline() on closed filehandle GEN1 at t line 17.
Doing a close seems to maintain some information about the filehandle, and the variable stays defined. Doing an undef unsurprisingly undefs the variable, so you get a slightly different warning, and an extra one about it being udnefined.
