Suggest a mnemonic for piped open

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hello

Yet again, I find myself forgetting which way round to to write a piped open in perl. I have just written:

open my $sort_FH, '-|', 'sort | uniq > '. $sorted_out_file or die "Error starting sort process $!";

When I should have used '|-'.

Can anyone suggest a mnemonic to help remember which way around the pipe and minus symbols go?

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Re: Suggest a mnemonic for piped open by choroba (Cardinal) on Jan 30, 2012 at 10:41 UTC
From the documentation: In the 2-arguments (and 1-argument) form one should replace dash ('-') with the command.	[reply]
Re: Suggest a mnemonic for piped open by ikegami (Patriarch) on Jan 30, 2012 at 12:12 UTC
It's never clear, but it's a bit clearer with 2-arg version. `open my $sort_FH, '\| sort \| uniq > '. $sorted_out_file` [download] In the 3-arg version, the command is replaced with "-". `open my $sort_FH, '\|-', 'sort \| uniq > '. $sorted_out_file` [download]	[reply] [d/l] [select]
Re: Suggest a mnemonic for piped open by BrowserUk (Patriarch) on Jan 30, 2012 at 13:08 UTC
Another way of thinking about it that might work for you. Place an imaginary 'perl' the other side of the pipe from the command. Then perl `'\| command'` becomes: perl supplying input to the command. And `'command \|'` perl becomes: the command suppying input to perl. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. The start of some sanity?	[reply] [d/l] [select]
Re: Suggest a mnemonic for piped open by BrowserUk (Patriarch) on Jan 30, 2012 at 12:30 UTC
Not particularly mnemonic, but it's my best effort of putting what I think, when writing or reading the constructs, into words ... When the pipe is on the way in to the command: `'\| command'` it is supplying input to the command. When the pipe in on the way out from the command: `'command \|'` it is receiving output from the command. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. The start of some sanity?	[reply] [d/l] [select]