Why don't here strings in Makefiles using Bash work?

Question

I just solved a problem with my Makefile(s). Make trips over every <<< with the error message

/bin/sh: 1: Syntax error: redirection unexpected

And I would like to know why. (I am using Bash as SHELL)

In my current projects I tried a lot of recipies along the lines of:

target:
    read FOO <<< "XXX"; \
    read BAR <<< "YYY"; \
    read BAZ <<< "ZZZ"; \
    someprog -a param0 -b $$FOO -c param1 -d $${BAR} -e param2 -f $${BAZ} >$@

Trying this will result in an error for every <<< as described at the beginning. My workaround is

target.dep:
    echo "XXX YYY ZZZ" >$@

target: %: %.dep
    read FOO BAR BAZ < $<;\
    someprog -a param0 -b $$FOO -c param1 -d $${BAR} -e param2 -f $${BAZ} >$@

which means I put my stuff into temporary files which I then read with <, which works just fine. When I copy paste my make output to a normal bash prompt, every command works just as expected, even with the <<<. I am fairly certain that my problem is, that using the <<< operator, i.e. here strings, break something. Why is that and is there a way to make here strings work in Makefiles?

P.S.: Yes, sometimes I feel autotools would be the better choice over make.

Answer 1

/bin/sh: 1: Syntax error: redirection unexpected

means you’re not using bash as your shell, in spite of your expectations to the contrary. bash as sh recognises here strings fine (so your Makefile would work on Fedora), but for example dash as sh doesn’t. Unless told otherwise, Make uses /bin/sh as its shell; it ignores your default user shell.

Setting

SHELL=/bin/bash

in your Makefile should fix things for you; at least, it does for me on a system showing the same symptoms as yours.

P.S.: Yes, sometimes I feel autotools would be the better choice over make.

Autotools and Make don’t address the same problems; they’re complementary, and using Autotools would still mean using Make...

Answer 2

As you can see in the error message, the shell that make invokes is not bash but /bin/sh. sh does not generally understand here-strings.

If you set the make variable SHELL to /bin/bash (or whatever the path is for that shell on your system), it will use bash instead of sh.

See also the relevant GNU make documentation about this at https://www.gnu.org/software/make/manual/html_node/Choosing-the-Shell.html