Re^2: -p option with __DATA_

...which uses the 'diamond operator'. Normally, the diamond operator takes all the file names specified on the command line as arguments, combines the corresponding files into one big file, and then assigns a line from the big file to $_ each time through the loop. However, if you do not specify any file names as arguments on the command line, then the diamond operator reads from STDIN. Presumably, that is what you did, so your program is waiting for you to type in a line of text for the diamond operator to process (you would hit ctrl+D to signal end-of-file after typing in all your lines).

Also, when you specify filenames as arguments on the command line, if you specify a file name as: -, then the diamond operator will read from STDIN for that portion of the big file.

Comment on Re^2: -p option with __DATA__

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Re^3: -p option with __DATA__ by ikegami (Patriarch) on Nov 19, 2009 at 17:09 UTC
Normally, the diamond operator takes all the file names specified on the command line as arguments, Only when `ARGV` is provided as the handle or not handle is provided (since the diamond operator uses `ARGV` by default). That's because the diamond operator does none of that. It's all `ARGV`'s doing. combines the corresponding files into one big file Yes, without actually combining the files on disk or in mem. In fact, using `eof` (with no argument or parens), you can detect when it's going to move to another file. and then assigns a line from the big file to $_ each time through the loop No, the diamond operator neither creates a loop nor assigns to `$_`. `while` provides the looping. However, if you do not specify any file names as arguments on the command line, then the diamond operator reads from STDIN. Again, only if ARGV is used as the handle since it's all `ARGV`'s doing. if you specify a file name as: -, then the diamond operator will read from STDIN for that portion of the big file. `ARGV` uses the two arg version of `open`. It also allows arguments such as `'zcat compressed.gz \|'`. In other words, without using a shell, you can achieve the same using `bash`'s `<( zcat compressed.gz )`	[reply] [d/l] [select]

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Re^3: -p option with __DATA__
by ikegami (Patriarch) on Nov 19, 2009 at 17:09 UTC

Normally, the diamond operator takes all the file names specified on the command line as arguments,

Only when ARGV is provided as the handle or not handle is provided (since the diamond operator uses ARGV by default). That's because the diamond operator does none of that. It's all ARGV's doing.

combines the corresponding files into one big file

Yes, without actually combining the files on disk or in mem. In fact, using eof (with no argument or parens), you can detect when it's going to move to another file.

and then assigns a line from the big file to $_ each time through the loop

No, the diamond operator neither creates a loop nor assigns to $_. while provides the looping.

However, if you do not specify any file names as arguments on the command line, then the diamond operator reads from STDIN.

Again, only if ARGV is used as the handle since it's all ARGV's doing.

if you specify a file name as: -, then the diamond operator will read from STDIN for that portion of the big file.

ARGV uses the two arg version of open. It also allows arguments such as 'zcat compressed.gz |'. In other words, without using a shell, you can achieve the same using bash's <( zcat compressed.gz )

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