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

Am 10.10.2014 um 20:48 schrieb David Aguilar:

On Fri, Oct 10, 2014 at 01:19:40PM +0200, Jakub Narębski wrote:

quoted

David Aguilar wrote:

quoted

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 <redacted>
Helped-by: Junio C Hamano [off-list ref]
Signed-off-by: David Aguilar <redacted>
---

quoted

+	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