I have some code which evals a configuration file - but before doing so
attempts to validate the content. It does this by taking each potential
keyword from the file and then doing:
if typeset -p | grep -q "^declare -. ${var}$”; then
… to determine whether the keyword in question exists as a declared but unset
variable in the script.
However, I am seeing cases where the above incorrectly fails, or where
executing this line twice in immediate succession will fail on the first
invocation and then succeed on the second. This doesn’t happen every time, and
appears to be non-deterministic: running the entire script multiple times
sometimes results in an earlier failure, sometimes it continues succeeding for
many iterations more. Turning on xtrace or adding additional debug logging
does appear to prevent the problem from occurring, unfortunately.
Sometimes, with much less regularity, the above line actually fails with:
<script name>: typeset: write error: Broken pipe
The problem I’m hitting may be specific to Ubuntu 14.04 LTS’
bash-4.3.11(1)-release or may only occur within a VM environment - but it looks
as if it may be a timing-based issue or a race-condition… although putting a
‘sleep 0.1’ before the typeset call appears to make little or no difference.
Additionally, I can’t reproduce this behaviour on bash-4.4.
Is this or anything similar a known issue with bash-4.3 which has been
specifically fixed (and if so, is there a URL or mailing list entry which
documents this?) or is it something which anyone else has ever come across or
reported?
Failing this, is there any alternative to ‘typeset’ to list a variable declared
as local to a function but which has not yet been assigned a value?
