[ruby-core:97812] [Ruby master Bug#14413] `-n` and `-p` flags break when stdout is closed

Issue #14413 has been updated by akr (Akira Tanaka).


I like silent exit at EPIPE on STDOUT.

The error message of `ruby ... | head` doesn't help us.
The user, who types the command line, knows the ruby process cannot continue to output to STDOUT after EPIPE.

Alto, I think it's Unix-ish.

These reasons doesn't depend on -p/-n option.
So I advocated (at a developer meeting) to change
the behavior at EPIPE on STDOUT regardless of -p/-n option.

However, it would be dangerous for other IOs, such as sockets.
So, the change should not affect to all IOs.
(STDERR would be changeable, though.)



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Bug #14413: `-n` and `-p` flags break when stdout is closed
https://bugs.ruby-lang.org/issues/14413#change-85030

* Author: josh.cheek (Josh Cheek)
* Status: Feedback
* Priority: Normal
* ruby -v: ruby 2.5.0preview1 (2017-10-10 trunk 60153) [x86_64-darwin16]
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
Ruby generally works well within a pipeline. The `-n` and `-p` flags are incredibly useful. However, it is common practice to use programs like `head` and `sed`, which will close the pipe after completing their job. This is convenient, because often it limits an expensive amount of output to a workable subset. I can figure out the pipeline for a subset of input, and then remove the limiting function.

However, Ruby explodes with `-e:1:in `write': Broken pipe @ io_write - <STDOUT> (Errno::EPIPE)`, when it writes the current line to stdout. When in a line oriented mode, and stdout closes, I think it should exit successfully (so it doesn't break bash scripts with `pipe fail`set) and silently (no error message), hence marking this a bug report rather than a feature request.

I've attached a screenshot to show that this is how every other program works, that I tried.

~~~
git clone https://github.com/jquery/esprima
cd esprima/test/fixtures/
ls                                                                             | head -1 # ls
find . -type f -name '*json'                                                   | head -1 # find
find . -type f -name '*json' | head -1 | xargs cat | jq .                      | head -1 # jq
find . -type f -name '*json' | grep -v JSX | grep -v tokenize                  | head -1 # grep
find . -type f -name '*json' | sed -E '/JSX|tokenize/d'                        | head -1 # sed
find . -type f -name '*json' | awk '/JSX|tokenize/ { next }; { print }'        | head -1 # awk
find . -type f -name '*json' | perl -e 'while(<>) { /JSX|tokenize/ || print }' | head -1 # perl
find . -type f -name '*json' | ruby -ne 'print unless /JSX|tokenize/'          | head -1 # ruby :(
~~~

---Files--------------------------------
Screen Shot 2018-01-27 at 7.27.49 PM.png (458 KB)
Screen Shot 2020-04-03 at 2.58.41 PM.png (158 KB)


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