Allan McRae wrote:
Cedric Staniewski wrote:
For some packages, generally the 'any' arch ones, a build step is not required and therefore can be skipped. In these cases, a package() function without a build() one is sufficient.
As a side effect, this commit makes meta packages without any function at all in the PKGBUILD possible.
Fixes FS#15147.
Signed-off-by: Cedric Staniewski <cedric@gmx.ca> --- <snip>
+# test for available PKGBUILD functions +# The exclamation mark is required here to avoid triggering the ERR trap when +# a tested function does not exist. +if [[ $(! type -t build) = "function" ]]; then + BUILDFUNC=1 +fi
This certainly appears to work, but can you explain how? Here is my understanding. The "!" means that when build() is not present, the function will still return 0 (not triggering the err trap) and the comparison then fails. When build() function is present, the type -t... outputs "function" but returns 1. How is the err trap not set of then? Is it because there is a value output?
There is no real explanation, only "that's how it works in bash". ;)
From bash's manpage:
trap [-lp] [[arg] sigspec ...] [...] The ERR trap is not executed if the failed command is part of the command list immediately following a while or until keyword, part of the test in an if statement, part of a command executed in a && or || list, or if the command's return value is being inverted via !.
Note that apparently only the test/[ builtin is meant here. Your explanation is correct for return codes, but it is not applicable here, because the ERR signal is not the same as a return code greater than zero. Given this script: ----------------- #!/bin/bash set -E trap 'echo >&2 "error"' ERR echo test1 type -t package echo ret: $? echo echo test2 ! type -t package echo ret: $? echo echo test3 type -t package || echo 1 echo ret: $? echo echo test4 type -t package && echo 1 echo ret: $? echo ----------------- It will generate the following output.
$ ./test.sh test1 error ret: 1
test2 ret: 0
test3 1 ret: 0
test4 ret: 1
The interesting case is the last one. "type -t package" returns the return code 1 and an ERR signal, but the ERR trap is not triggered, even though "echo 1" is actually never executed. So, there are several possibilities to catch the ERR signal and I only went for the exclamation mark, because it is the shortest one :). It would also be possible to use "|| echo" if you think it is easier to understand, however, it implies a wrong assumption (return code > 0 = ERR) in my opinion and the "echo" is not needed here.
Anyway, this is certainly a good catch for when applying the [[ & (( patch. The rest of the patch looks good to me.
I thought I already comment about this in the thread. Anyway, you are aware of it now.
Allan