How to handle shell expansions in GNU Make under Ubuntu? - bash

Question

Given this very simple Makefile:
all:
#mkdir -pv test/{a,b}
I get this output on OS X 10.6.8 and CentOS 5.5:
mkdir: created directory `test'
mkdir: created directory `test/a'
mkdir: created directory `test/b'
But on Ubuntu 11.04 I get this:
mkdir: created directory `test'
mkdir: created directory `test/{a,b}'
Running the command mkdir -pv test/{a,b} manually in the shell on all platforms gives the expected result.
The version of GNU Make is the same on all platforms:
GNU Make 3.81
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
This program is built for [PLATFORM]
What's different under Ubuntu and why doesn't the shell expansion work there?

Answer 1

The problem is probably that Make spawns /bin/sh. It is usually a symlink to your system's default shell.
Option 1
You could make sure it points to bash (as this is a bashism). Probably, it is now /bin/dash or /bin/sh, depending on your version of Ubuntu.
Option 2
Easier option:
SHELL=/bin/bash
all:
#echo a{3,4}
#bash -c 'echo a{3,4}'
This prints the same output twice unless you comment-out the SHELL= line
Option 3
If you can't/don't want to modify the make file, you can invoke it like so:
make SHELL=/bin/bash
beware of interactions with sub-makefiles or includes. You might want to look at the make -e option and the make export keyword: http://www.gnu.org/s/hello/manual/make/Variables_002fRecursion.html

Answer 2

Make has a function to do this:
#mkdir -pv $(addprefix test/,a b)
gets expanded to
#mkdir -pv test/a test/b
The docs are very thorough.

Answer 3

It's been a long, long time since I've used Make...
There are several ways to specify a particular shell to use. The default shell for old Make was the original Bourne shell. If you wanted a different shell, you had to set it yourself.
You're using Linux and GNU, so I'll assume that you're using BASH as the default shell. Try this command in your Make:
echo "random = $RANDOM"
If this simply prints random = and doesn't include a random number, your Make is using Bourne shell as its default shell instead of BASH. (Which is weird because I didn't think there was a real Bourne shell in Linux...) To get around this:
You can add in a SHELL macro pointing to the BASH shell.
You can include the shell in your command.
Instead of:
#mkdir -pv test/{a,b}
Put this:
/bin/bash -c #mkdir -pv test/{a,b}
This specifies you want to use BASH and not the standard /bin/sh Bourne shell.
If the echo random = $RANDOM does print a random number, you're using BASH (or at least Kornshell), but the BRACE EXPANSION might not be set. Try using this in your Makefile:
set -o
And make sure braceexpand is on. It could be off when you run Make.