Re^2: Printing to STDOUT buffered when invoking Perl within a bash-script using tee

I have tried this but the fact the Perl script is NOT buffered when ran as a standalone script or when tee/exec is not used within the Bash script suggests to me it's not an issue with the Perl script itself but rather it's interaction with the Bash.

Update 1: I had tried $|=1; however the fact that NO buffering occurs when the Perl script is run as a standalone or when exec/tee is not used within the Bash script, suggests to me that it's not an issue inherent to the Perl but rather a problem with its interaction with Bash.

Update 2: $|=1; now appears to work and solves the issue - i'm not sure why it did not before.

Comment on Re^2: Printing to STDOUT buffered when invoking Perl within a bash-script using tee

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Re^3: Printing to STDOUT buffered when invoking Perl within a bash-script using tee by haukex (Archbishop) on Dec 05, 2016 at 15:24 UTC
Hi TJCooper, the Perl script is NOT buffered when ran as a standalone script A described in the article I linked to, Perl decides whether STDOUT should be line or block buffered depending on whether it is connected to a terminal or not. For example, you should notice a difference in the behavior of the following: the middle one delays its output until the end due to the buffering. `$ perl -le 'for (0..10) { print; sleep 1 }' $ perl -le 'for (0..10) { print; sleep 1 }' \| tee /tmp/foo $ perl -le '$\|=1; for (0..10) { print; sleep 1 }' \| tee /tmp/foo` [download] I have tried this In the following bash script, if I remove the `$\|=1;`, it displays the undesired behavior you describe; with the autoflush turned on it shows the expected "live" view. `#!/bin/bash exec > >(tee "/tmp/foo") perl -le '$\|=1; for (0..10) { print; sleep 1 }'` [download] So if you've tried `$\|=1;` and are still getting the undesired behavior, perhaps you could show a Short, Self Contained, Correct (Compatible) Example for us to reproduce the problem. ... after your update to the node while I was typing my reply: I had tried using that magic-variable and it did not work...but now it does. Please see How do I change/delete my post?, especially "It is uncool to update a node in a way that renders replies confusing or meaningless". Regards, -- Hauke D Update: Referenced article.	[reply] [d/l] [select]

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Re^3: Printing to STDOUT buffered when invoking Perl within a bash-script using tee
by haukex (Archbishop) on Dec 05, 2016 at 15:24 UTC

Hi TJCooper,

the Perl script is NOT buffered when ran as a standalone script

A described in the article I linked to, Perl decides whether STDOUT should be line or block buffered depending on whether it is connected to a terminal or not. For example, you should notice a difference in the behavior of the following: the middle one delays its output until the end due to the buffering.

$ perl -le 'for (0..10) { print; sleep 1 }'
$ perl -le 'for (0..10) { print; sleep 1 }' | tee /tmp/foo
$ perl -le '$|=1; for (0..10) { print; sleep 1 }' | tee /tmp/foo
[download]

I have tried this

In the following bash script, if I remove the $|=1;, it displays the undesired behavior you describe; with the autoflush turned on it shows the expected "live" view.

#!/bin/bash
exec > >(tee "/tmp/foo")
perl -le '$|=1; for (0..10) { print; sleep 1 }'
[download]

So if you've tried $|=1; and are still getting the undesired behavior, perhaps you could show a Short, Self Contained, Correct (Compatible) Example for us to reproduce the problem.

... after your update to the node while I was typing my reply:

I had tried using that magic-variable and it did not work...but now it does.

Please see How do I change/delete my post?, especially "It is uncool to update a node in a way that renders replies confusing or meaningless".

Regards,
-- Hauke D

Update: Referenced article.

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