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Re: sh embedding

From: Philip Guenther
Subject: Re: sh embedding
Date: Mon, 23 Jul 2012 13:03:28 -0700

On Mon, Jul 23, 2012 at 11:59 AM, icegood <address@hidden> wrote:
> from newer version of gnu make (3.81 under kubuntu 12.04)
> .PHONEY: all
> all:
>         if [ \( "$$(ls *.lock 2>/dev/null)" == "" \) ]; then \

The '==' operator is a bash extension that is supported by many but
not all shells.  Perhaps the shell seen by make on your kubuntu system
is one that doesn't support it?  The portable (30+ years!) equality
operator is "=".

(The '==' operator was an extension that improved usability but added
no new functionality and instead reduced portability; thanks, bash
maintainers, for screwing everyone by making that tradeoff!)

>     touch address@hidden; \

This "check for lock file, if it doesn't exist then create it"
operation is *not* 100% safe!  If two makes are run at almost the same
time, they may both see the file doesn't exist and then both touch the
lock file and continue, so the lock file is not actually guaranteeing
that only one copy is running.  You should see if there's a real
atomic lock file program on your system that you can use for this.
For example, I see a "flock" program on a Redhat system that could be
used, those the usage is a bit different.

>     if [ \( ! -e $@ \) -o \( ../$(tag_fn) -nt $@ \) ]; then \
>       echo $@ done; \
>     else \
>       touch $@; \
>     fi; \

Isn't this the same as making $(tag_fn) a dependency of 'all' and
having 'all' *not* be PHONY?

>     rm -f address@hidden; \
>   else \
>     sleep 1; \
>   fi;

If the lock cannot be obtained, you just sleep a second and then
return success?  Why not at least "exit 1" there so that the caller
can tell that the make failed in a consistent fashion?

Philip Guenther

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