Write a multi-line command in a Makefile

By Thomas Taylor | | 2 minutes
Makefile

Occasionally, there is a need for adding multiple continuous lines for one target in a Makefile.

Writing multiple lines for a target

Executing multiple commands in a target is trivial:

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test:
	@echo 1
	@echo 2

Output:

1
2

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2

However, each line is executed in its own shell. If a continuous line is needed, the following rules must be applied:

  1. Use $$ instead of $
  2. Terminate each line using a semicolon ;
  3. Add a trailing backslash at the ending of the line \
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test:
	var1=test; \
	echo $$var1

Output:

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var1=test; \
echo $var1
test

A real use case using multi-line targets

For how.wtf, the CI/CD process invalidates a CloudFront distribution via id.

For context, the aws dependency verifies that aws is executable prior to the command execution. More information on that here.

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.PHONY: invalidate
invalidate: aws
	distribution_id=$$(aws cloudfront list-distributions --query "DistributionList.Items[?starts_with(Origins.Items[0].DomainName, '$(BUCKET)')].Id" --output text); \
	aws cloudfront create-invalidation \
		--distribution-id $$distribution_id \
		--paths "/*" \
		--query "Invalidation.Id" \
		--output text

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distribution_id=$(aws cloudfront list-distributions --query "DistributionList.Items[?starts_with(Origins.Items[0].DomainName, 'how.wtf')].Id" --output text); \
aws cloudfront create-invalidation \
	--distribution-id $distribution_id \
	--paths "/*" \
	--query "Invalidation.Id" \
	--output text
ID6WOFMWKLCYDYRUA6AGPXXXXX

Writing multiple lines using ONESHELL

The ONESHELL directive allows multiple lines to executed in the same shell; however, special characters like @, -, and + are interpreted differently.

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.ONESHELL:
test:
	var1=test
	echo $$var1

Output:

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var1=test
echo $var1
test