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 --- <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

Isaac Good wrote:

On Sun, Nov 01, 2009 at 05:45:27PM +0000, Cedric Staniewski wrote:

...

Allan McRae wrote:

...

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.

I get the same results with both test/[ as with [[

Reusing your code,

...

set -E trap 'echo >&2 "error"' ERR

false [ false ] [[ false ]] (( 0 )) ! true

Only the 'false' by itself triggers the trap. [ and [[ and treated the same.

You missed a small, but important part of the sentence:

part of the test *in an if statement*

Consequently, this script -------------------- #!/bin/bash set -E trap 'echo >&2 "error"' ERR echo test1 if test $(type -t package); then echo 1 fi echo test2 if [ $(type -t package) ]; then echo 1 fi echo test3 if [[ $(type -t package) ]]; then echo 1 fi echo test4 if (( $(type -t package) )); then echo 1 fi -------------------- results in $ ./test.sh test1 test2 test3 error test4 error

On Sun, Nov 01, 2009 at 07:29:20PM +0000, Cedric Staniewski wrote:

Isaac Good wrote:

...

On Sun, Nov 01, 2009 at 05:45:27PM +0000, Cedric Staniewski wrote:

...

Allan McRae wrote:

...

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.

I get the same results with both test/[ as with [[

Reusing your code,

...

set -E trap 'echo >&2 "error"' ERR

false [ false ] [[ false ]] (( 0 )) ! true

Only the 'false' by itself triggers the trap. [ and [[ and treated the same.

You missed a small, but important part of the sentence:

...

part of the test *in an if statement*

Consequently, this script -------------------- #!/bin/bash set -E trap 'echo >&2 "error"' ERR

echo test1 if test $(type -t package); then echo 1 fi

echo test2 if [ $(type -t package) ]; then echo 1 fi

echo test3 if [[ $(type -t package) ]]; then echo 1 fi

echo test4 if (( $(type -t package) )); then echo 1 fi --------------------

results in

$ ./test.sh test1 test2 test3 error test4 error

I brought this up in FreeNode/#bash and at the very least there is an error in the man pages. More likely a bug in [[. This should be reported upstream to Chet (bash). - Isaac