Subject: Re: [PATCH v2] mergetool: use more conservative temporary filenames

From: Johannes Sixt <[email-masked]>
Date: Fri, 10 Oct 2014 21:54:29 +0200

Am 10.10.2014 um 20:48 schrieb David Aguilar:
> On Fri, Oct 10, 2014 at 01:19:40PM +0200, Jakub Narębski wrote:
>> David Aguilar wrote:
>>> Avoid filenames with multiple dots so that overly-picky tools do
>>> not misinterpret their extension.
>>>
>>> Previously, foo/bar.ext in the worktree would result in e.g.
>>>
>>> 	./foo/bar.ext.BASE.1234.ext
>>>
>>> This can be improved by having only a single .ext and using
>>> underscore instead of dot so that the extension cannot be
>>> misinterpreted.  The resulting path becomes:
>>>
>>> 	./foo/bar_BASE_1234.ext
>>>
>>> Suggested-by: Sergio Ferrero <[email-masked]>
>>> Helped-by: Junio C Hamano <[email-masked]>
>>> Signed-off-by: David Aguilar <[email-masked]>
>>> ---
>>
>>> +	if BASE=$(expr "$MERGED" : '\(.*\)\.[^/]*$')
>>> +	then
>>> +		ext=$(expr "$MERGED" : '.*\(\.[^/]*\)$')
>>> +	else
>>> +		BASE=$MERGED
>>> +		ext=
>>> +	fi
>>
>> Why use expr and not POSIX shell parameter substitution?
>>
>> BASE=${MERGED%.*}
>> ext=.${MERGED##*.}
>>
>> Or something like that...
> 
> Thanks for the sug.
> 
> My POSIX shell parameter expansion-fu is not super advanced, but
> if you can help me rework it I'd be happy to reroll.
> 
> It does seem simple and robust with expr, though.  Extending the
> parameter expansion approach to work in all cases may end up
> with more complexity than with the expr method, it seems.
> 
> Here are the use cases:
> 
> 	$ MERGED=foo.bar.baz && echo ${MERGED%.*} ${MERGED##*.}
> 	foo.bar baz
> 
> Good.
> 
> 	$ MERGED=foo && echo ${MERGED%.*} ${MERGED##*.}
> 	foo foo
> 
> Bad.
> There's no extension and the substitution doesn't handle it.
> 
> 	$ MERGED=foo.bar/baz && echo ${MERGED%.*} ${MERGED##*.}
> 	foo bar/baz
> 
> Bad.
> There's no extension but the substitution thinks the parent directory's
> extension-less name is the basename, and thinks that bar/baz is the extension.
> 
> I am curious to know whether there's a nice and elegant way to do it
> with shell expansions.  Let me know what you think.

It's not exactly elegant to do it:

First, you extract the last path part:

	file=${MERGED##*/}

Then the directory including the trailing slash:

	dir=${MERGED%"$file"}

Then the basename without an extension:

	base=${file%.*}

Finally the extension including the dot:

	ext=${file#"$base"}

Beware of empty $base and $dir (e.g., for files named .gitignore or so)

-- Hannes