Reply to Eric Blake,
At this time, I do not have a Linux image available to me. If
you saw the same behavior on Fedora, then I suggest the behavior
originates upstream at or close the the GNU source-code level.
Mr. Penny's response asserted the observed behavior "is intended
behavior", in which case there should exist a GNU specification
document describing the intended pipe STDIN re-direction
restrictions for 'mapfile', 'read' and possibly other "builtins".
Lacking such a reference nothing can be said about intent.
Implementation-as-intent implies errors and conceptual and
behavioral inconsistencies in the implementation were intended.
I decline to think that of the distributed BASH maintenance team.
He provided a reference to
http://mywiki.wooledge.org/BashFAQ/024, where, if you read the
page, the behavior inconsistency I reported is shown under the
heading of "More broken stuff:". I take that "More broken
stuff:" opinion to mean yet others read the same surface
discrepancy between doc and behavior as I did.
I believe what we have at this point is:
A) GNU doc lacking nuance, attention to consistent terminology,
and helpful rule-statement to code example/counter-example
illustrations adjacent to rule statements. For a doc
counter-example, the Open Group doc at
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html
does make an effort to distinguish behaviors between "2.14
Special Built-In Utilities" and "2.9.1 Simple Commands" whereas
the GNU doc indiscriminately mixes the words "commands" (section
3.2) and "builtin" and "command" and the phrase "builtin command"
(section 4) as if their behaviors are identical under the section
4 title of "Shell Builtin Commands"
(https://www.gnu.org/software/bash/manual/html_node/Shell-Builtin-Commands.html#Shell-Builtin-Commands).
The GNU doc for shopt lastpipeis fairly opaque unless you have
deep knowledge and that knowledge is cued when considering the
possible meanings of "current shell environment" for built-ins
(same process) vs. external child-process executables.
B) However conceptually inconsistent, an obsessive BASH doc
reader could imply the observed bash built-ins behavior by
integrating multiple hints and rule statements scattered across
the GNU doc and then, crucially, doubting the plain meaning of
the unqualified doc statements of "Read lines from the standard
input..." .
Thank you for your response.
Regards,
UN*X Since '85
On 7/20/2018 12:08 PM, Eric Blake wrote:
On 07/17/2018 08:52 PM, BloomingAzaleas wrote:
Reply to Steven Penny <svnpenn at gmail dot com>:
no mis-behaving: this is intended behavior - you yourself
have given
workarounds: either redirect output to a file that can be
later read, or pipe to
command grouping ala {} or () and read stdin from inside
the subshell
I suggest the following adjustment to the man pages inserting
a parenthetical cue regards behavior in pipes:
Is the behavior you are complaining about unique to Cygwin, or
can it be reproduced on a GNU/Linux box? If the latter, then
an upstream bug report is better than asking for a
cygwin-specific patch. [Hint - as the maintainer of the cygwin
bash port, I don't recall adding any cygwin-specific tweaks for
mapfile - and a quick test on Fedora shows the same behaviors]
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