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From: | david kerns |
Subject: | Re: [bug-gawk] Behavior of fflush with SIGPIPE on stdout |
Date: | Tue, 7 Mar 2017 09:25:44 -0700 |
Hi,
After a recent OS upgrade on the only machine where I do heavy awk work, I got caught by a regression dated 2013 in gawk, namely the one about "ignored SIGPIPE".
Basically, what happens is that the ages-old unix idiom
infinite-data-source | filter | head
fails if "filter" is a post-2013 gawk using explicit fflush().
Example:
yes | awk '{print;fflush(stdout)}' | head
Of course this is a cooked example, but I guess you can imagine the real-life situations where explicit fflush() is needed, with appropriate task-dependent granularity, for performance and interactivity.
Looking at the comments in main.c, I do not see whether this regression was considered or not.
It rather looks like the idea of "writing to a pipe" was generally thought about in the context of additional fds ("print ... | cmd"), but that the simple, obvious case of
- gawk used as a unix filter
- stdout is a pipe
was overlooked.
I assume this is just a shallow search on my part; thanks in advance for giving pointers to the relevant discussion and release notes announcing this regression, and the idiomatic ways to avoid it.
-Alex
PS: Note that crude versions of awk like "mawk" don't have the issue, but I need gawk for the obvious reasons.
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