How to use sed in a Makefile

Question

I have tried putting the following in my Makefile:

@if [ $(DEMO) -eq 0 ]; then \     cat sys.conf | sed -e "s#^public_demo[\s=].*$#public_demo=0#" >sys.conf.temp; \ else \     cat sys.conf | sed -e "s#^public_demo[\s=].*$#public_demo=1#" >sys.conf.temp; \ fi 

but when I run make, I get the following error:

sed: -e expression #1, char 30: unterminated `s' command 

If I run the exact lines that contain sed in the console, they behave correctly.

Why am I getting this error and how can the problem be fixed?

Answer 1

TL;DR: Use single quotes and use two $ signs. The expression is expanded twice, once by make and once by bash. The rest of this answer provides further context.

It might be the $ sign in the substitution that is interpreted by make as a variable. Try using two of them like .*$$#public_demo. Then make will expand that to a single $.

EDIT: This was only half the answer. As cristis answered: the other part is that one needs to use single quotes to prevent bash from expanding the $ sign too.

Answer 2

I suggest you use single quotes instead of double quotes, the $ might be processed as a special char by make before running sed:

cat sys.conf | sed -e 's#^public_demo[\s=].*$#public_demo=0#' >sys.conf.temp;