How can I use Bash syntax in Makefile targets?

user_60628 0
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I often find Bash syntax very helpful, e.g. process substitution like in diff <(sort file1) <(sort file2).

Is it possible to use such Bash commands in a Makefile? I'm thinking of something like this:

file-differences:
    diff <(sort file1) <(sort file2) > $@

In my GNU Make 3.80 this will give an error since it uses the shell instead of bash to execute the commands.

shell makefile bash
7 Answers

From the GNU Make documentation,

5.3.2 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.

derobert_277270

You can call bash directly, use the -c flag:

bash -c "diff <(sort file1) <(sort file2) > $@"

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).

Chris_Lutz_607770

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_16212320

You can call bash directly within your Makefile instead of using the default shell:

bash -c "ls -al"

instead of:

ls -al
user_148600

It's not a direct answer to the question, makeit is limited Makefile replacement with bash syntax and it can be useful in some cases (I'm the author)

  • rules can be defined as bash-functions
  • auto-completion feature

Basic idea is to have while loop in the end of the script:

while [ $# != 0 ]; do
  if [ "$(type -t $1)" == 'function' ]; then
    $1 
  else
    exit 1
  fi 
  shift
done

https://asciinema.org/a/435159

user_35645900
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