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Re: Directing into a variable doesn't work

From: Martijn Dekker
Subject: Re: Directing into a variable doesn't work
Date: Sun, 24 Jun 2018 12:38:27 +0200
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:52.0) Gecko/20100101 Thunderbird/52.7.0

Op 24-06-18 om 05:08 schreef Peter Passchier:
With memory being abundant and filesystem access expensive, I want to
put stdout and stderr of a command into variables (without needing to
write to a file):

output=$($command 2>>>errors)

This would not work even if the feature is implemented. The $(command substitution) forks a subshell process to execute the command in, because the main shell process needs a process it can set up a pipe with. So the 'errors' variable would only exist in that subshell process and would be lost as soon as the command substitution completes.


$command >>>output 2>>>errors

This form seems conceivable to me.

However, note that here-documents and here-strings internally use temporary files, so they do involve file system access. I'm not Chet, but I don't think that would be different for your proposed feature. So while this might be some nice syntactic sugar, I'm afraid you would be disappointed about the performance.

I still kind of like the idea, though. As far as I know, there's currently no way to capture more than one output stream into separate variables without involving rather laborious handling of temporary files. Your proposal would probably still involve that, but the shell would do the hard work for you which seems like an improvement to me.

BTW, 'reverse here-document' doesn't sound quite right. You're not specifying any document or string containing input, you're specifying a variable in which to store output. So, here-variable?

- M.

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