Re^2: Differentiating STDIN from arguments when using -n ?

I tried this but somehow $x seems to become undef after the first time through the implicit loop.

$ cat gibberish
This is a couple
of lines of crud
$ cat gibberish | perl -Mstrict -Mwarnings -ne '
> my $x;
> BEGIN {$x = shift @ARGV; print qq{BEGIN - $x\n}}
> print qq{x = $x\n$_};' myarg
BEGIN - myarg
x = myarg
This is a couple
Use of uninitialized value in concatenation (.) or string at -e line 4
+, <> line 2.
x = 
of lines of crud
$
[download]

I wonder what is causing this.

Cheers,

JohnGG

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Re^3: Differentiating STDIN from arguments when using -n ? by bart (Canon) on Sep 15, 2007 at 11:53 UTC
Don't declare the $x — it's just a one-liner. Perl wraps a `while(<>) { ... }` loop around the code you put there (really!), so it's a new $x for every line in the file. See for yourself: `perl -n -MO=Deparse -e 'my $x' foo` [download] produces: `LINE: while (defined($_ = <ARGV>)) { my $x; } -e syntax OK` [download]	[reply] [d/l] [select]