Re^2: input from STDIN or from a file

also, there is a subtle difference between the <> operator and the implementation showed in the original post (although not very useful I think).

consider this:

$ cat test1.pl
#!/usr/bin/perl

use strict;
use warnings;

while (<>){
  print;
}

$ cat > testfile
two
three

$ echo "one" | perl test1.pl testfile
one
two
three

$ cat test2.pl
#!/usr/bin/perl

use strict;
use warnings;

my $file = shift @ARGV;

my $ifh;
my $is_stdin = 0;
if (defined $file){
  open $ifh, "<", $file or die $!;
} else {
  $ifh = *STDIN;
  $is_stdin++;
}

while (<$ifh>){
   print
}
close $ifh unless $is_stdin;

$ echo "one" | perl test2.pl testfile
two
three
[download]

That is, the <> operator acts like:

unshift(@ARGV, '-') unless @ARGV;
    while ($ARGV = shift) {
    open(ARGV, $ARGV);
    while (<ARGV>) {
        ...        # code for each line
    }
    }
[download]

i.e. processes STDIN AND any file given in the command line, while my implementation processes the file given in the command line OR STDIN.

citromatik

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Re^3: input from STDIN or from a file by Fletch (Bishop) on Jan 28, 2008 at 20:22 UTC
Erm, no it does either arguments or STDIN if none were given just like the documentation in perlop and the code you copied there from says. Read it again: `unshift( @ARGV, '-' ) unless @ARGV;` [download] Put a string `'-'` (which is shorthand to open to read from STDIN) onto the front of `@ARGV` unless there are already arguments in `@ARGV`. If you're getting the behavior you're seeing out of your `test1.pl` then something very strange is going on. `$ cat my_test1.pl #!/usr/bin/perl use strict; use warnings; while (<>){ print; } $ cat infile 2 from infile 3 from infile $ echo "testing" \| perl my_test1.pl infile 2 from infile 3 from infile` [download] The cake is a lie. The cake is a lie. The cake is a lie.	[reply] [d/l] [select]

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Re^3: input from STDIN or from a file
by Fletch (Bishop) on Jan 28, 2008 at 20:22 UTC

Erm, no it does either arguments or STDIN if none were given just like the documentation in perlop and the code you copied there from says. Read it again:

unshift( @ARGV, '-' ) unless @ARGV;
[download]

Put a string '-' (which is shorthand to open to read from STDIN) onto the front of @ARGV unless there are already arguments in @ARGV.

If you're getting the behavior you're seeing out of your test1.pl then something very strange is going on.

$ cat my_test1.pl                         
#!/usr/bin/perl

use strict;
use warnings;

while (<>){
  print;
}
$ cat infile                              
2 from infile
3 from infile
$ echo "testing" | perl my_test1.pl infile
2 from infile
3 from infile
[download]

The cake is a lie.
The cake is a lie.
The cake is a lie.

[reply]
[d/l]
[select]