How can I use Bash syntax in Makefile targets

Question

I often find Bash syntax very helpful  e g  process substitution like in diff  lt  sort file1   lt  sort file2    Is it possible to use such Bash commands in a Makefile  I m thinking of something like this   file-differences      diff  lt  sort file1   lt  sort file2   gt       In my GNU Make 3 80 this will give an error since it uses the shell instead of bash to execute the commands

User · Answer

If portability is important you may not want to depend on a specific shell in your Makefile  Not all environments have bash available

User · Answer

From the GNU Make documentation   5 3 1 Choosing the Shell ------------------------  The program used as the shell is taken from the variable  SHELL    If this variable is not set in your makefile  the program   bin sh  is used as the shell    So put SHELL     bin bash at the top of your makefile  and you should be good to go   BTW  You can also do this for one target  at least for GNU Make  Each target can have its own variable assignments  like this   all  a b  a       echo  a is   0   b  SHELL   bin bash     HERE  this is setting the shell for b only b       echo  b is   0    That ll print   a is  bin sh b is  bin bash   See  Target-specific Variable Values  in the documentation for more details  That line can go anywhere in the Makefile  it doesn t have to be immediately before the target

User · Answer

There is a way to do this without explicitly setting your SHELL variable to point to bash  This can be useful if you have many makefiles since SHELL isn t inherited by subsequent makefiles or taken from the environment  You also need to be sure that anyone who compiles your code configures their system this way   If you run sudo dpkg-reconfigure dash and answer  no  to the prompt  your system will not use dash as the default shell  It will then point to bash  at least in Ubuntu   Note that using dash as your system shell is a bit more efficient though

User · Answer

One way that also works is putting it this way in the first line of the your target   your-target    eval SHELL   bin bash       echo  here shell is   0

User · Answer

You can call bash directly  use the -c flag   bash -c  diff  lt  sort file1   lt  sort file2   gt        Of course  you may not be able to redirect to the variable     but when I tried to do this  I got -bash      ambiguous redirect as an error message  so you may want to look into that before you get too into this  though I m using bash 3 2 something  so maybe yours works differently

User · Answer

You can call bash directly within your Makefile instead of using the default shell   bash -c  ls -al    instead of   ls -al

[bash] How can I use Bash syntax in Makefile targets?

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