Hi Ian,
Ian Campbell <i...@hellion.org.uk> wrote:
> It seems there is an interesting (and new to me, or at least I'd never
> fully appreciated the behaviour) corner case of the `if $(foo); then`
> syntax, which is that if `foo` exits producing no output then its exit
> code is apparently used for the condition. If `foo` does produce output
> then the shell will attempt to execute that and use the resulting exit
> code.
>
> These just run true or false and take the output:
>
> $ dash -c 'if true ; then echo YES ; else echo NO ; fi'
> YES
> $ dash -c 'if false ; then echo YES ; else echo NO ; fi'
> NO
>
> These run true or false, see the output is "" and so use the exit code:
>
> $ dash -c 'if $(true) ; then echo YES ; else echo NO ; fi'
> YES
> $ dash -c 'if $(false) ; then echo YES ; else echo NO ; fi'
> NO
>
> These run `echo` (which always succeeds) then runs the resulting "true"
> or "false" and uses the exit code:
>
> $ dash -c 'if $(echo true) ; then echo YES ; else echo NO ; fi'
> YES
> $ dash -c 'if $(echo false) ; then echo YES ; else echo NO ; fi'
> NO
>
> This runs `echo` (which always succeeds) then tries to run the
> resulting "foo" and fails because that isn't a command:
>
> $ dash -c 'if $(echo bar) ; then echo YES ; else echo NO ; fi'
> dash: 1: bar: not found
> NO
>
> `git status` outputs nothing when the tree is clean, and I think the
> `$($git status -s -uno $DI_COPY/packages/po)` case uses that to succeed
> on a clean tree, however if the tree was dirty you'd get the "not
> found" stuff for something relating to the output.
>
> $ git status -s -uno build/Makefile
> $ echo $?
> 0
> $ dash -c 'if $(git status -s -uno build/Makefile ) ; then echo CLEAN ;
> else echo DIRTY ; fi'
> CLEAN
> $ echo "FOO" >> build/Makefile
> $ git status -s -uno build/Makefile
> M build/Makefile
> $ echo $?
> 0
> $ dash -c 'if $(git status -s -uno build/Makefile ) ; then echo CLEAN ;
> else echo DIRTY ; fi'
> dash: 1: M: not found
> DIRTY
>
> Notice that the original svn version had a `| grep -q ^C` which was
> checking if any line started with a "C" (for Changed I suppose),
> produced no output (`-q`) but exited with an error code reflecting the
> presence of any lines. You could do something similar but you'd need to
> check for more than M (modified) since git status has a variety of
> error codes, including (A)dded, (D)eleted, (R)enamed etc.
>
> `git status` doesn't seem to have an option which makes the error code
> reflect the dirtiness. In the past I've used:
>
> # Update cache, otherwise files which have an updated
> # timestamp but no actual changes are marked as changes
> # because `git diff-index` only uses the `lstat` result and
> # not the actual file contents. Running `git update-index
> # --refresh` updates the cache.
> git update-index -q --refresh
> if git diff-index --quiet HEAD -- path/to/something ; then clean ;
> else dirty ; fi
>
> (--quiet enable --exit-code which makes the exit status meaningful).
>
> For perhaps less git magic you could also just write it as:
> if [ -z "$(git status -s -uno path/to/something)" ] ; then clean ; else
> dirty ; fi
> or inversely:
> if [ -n "$(git status -s -uno path/to/something)" ] ; then dirty ; else
> clean ; fi
Thank you for your very detailed explanation!
First I will try to get it running with above (minimalist) variant.
Holger
--
============================================================
Created with Sylpheed 3.5.1 under
D E B I A N L I N U X 9 " S T R E T C H " .
Registered Linux User #311290 - https://linuxcounter.net/
============================================================
