"Dale R. Worley" <wor...@alum.mit.edu> writes:
>> $ if false; then :; fi | true; echo ${PIPESTATUS[*]}
>> 0 0
Trying to dissect this:
There are *three* pipelines that are executed:
1) 'if false; then :; fi | true'
2) 'false' (which is a pipeline, which is a list, which is the
conditional of the 'if')
3) 'echo ${PIPESTATUS[*]}'
The ':' is a pipeline but it isn't executed.
Note the treachery that (2) is entirely contained within (1), both
syntactically and in the time period of its execution.
The documentation (bash 5.1.0(1), yes I know it's really old) says:
PIPESTATUS
An array variable (see Arrays below) containing a list of exit
status values from the processes in the most-recently-executed
foreground pipeline (which may contain only a single command).
Note also that if all of the conditions of an 'if' are false, and it has
no 'else' clause, the 'if' exits with 0, that is, *true*. That is
counter-intuitive to me and so I misread the documentation of that the
first time.
However adjective "most-recently-executed" is rather ambiguous. In this
case:
A) The pipeline whose execution was most recently *started* is 'echo
${PIPESTATUS[*]}'.
B) The pipeline whose execution was most recently *completed* is 'if
false; then :; fi | true'.
C) The pipeline whose execution *has been completed* which was most
recently *started* is 'false'.
The evidence doesn't seem to be consistent with any of these three
definitions:
$ if false; then :; fi | false; echo ${PIPESTATUS[*]}
0 1
$ if false; then :; fi | true; echo ${PIPESTATUS[*]}
0 0
$ if false; then :; fi; echo ${PIPESTATUS[*]}
1
$
Note the difference in the behavior of the 2nd and 3rd examples.
Dale
