But it will fail if the infile looked like this: ;-)

    $ cat infile
    here
    comes
    trouble
    1
    2
[download]

--
John.

Have you tried your input? It works fine for me. As $_ isn't chomp()'d, it escapes the problem of modifying a readonly $1.

-sauoq
"My two cents aren't worth a dime.";

Have you tried your input?

Yes I tried the input.

I test everything before I post it here. I have a test directory full of files called file, file1, file2, numfile, bigfile, blankfile, etc.

Nevertheless, it is difficult to test for every eventuality. It looks like the behaviour changes between 5.6 and 5.8:

    $ perl5.005_03 -ne '$$_++||print' infile
    here
    comes
    trouble
    Modification of a read-only value attempted at -e line 1, <> chunk
+ 4.


    $ perl5.6.1 -ne '$$_++||print' infile
    here
    comes
    trouble
    Modification of a read-only value attempted at -e line 1, <> chunk
+ 4.

    $ perl5.8.0 -ne '$$_++||print' infile
    here
    comes
    trouble
    1
    2
[download]

--
John.

Here's a version which shouldn't rely on 5.8:

      01  2345678901234567
perl -ne '${_.$_}++||print'
[download]

-sauoq
"My two cents aren't worth a dime.";