make.md

GNU Make

Special variables

{target}: {prereq}

$@  = {target}
$<  = {prereq}}

.PHONY

A target which is always out-of-date even if file with same name exists.

.PHONY: clean
clean:              # always runs even if file called "clean" exists
    rm -rf *.o

Pipe failures

Dealing with commands involving pipes.

The problem

$? takes the exit status of the last command in the pipe. But you may want the target to fail if any command fails in the pipe.

test1:
    exit 1 | cat
    echo "Oh no, I'm still running"

Preferred solution

The following approach is for a single line:

test2;
    set -o pipefail; exit 1 | cat
    echo "This echo will not run and make will exit"

Alternative

The following affects the whole file:

test4:
    exit 1 | cat
    echo "Will not run"

SHELL=/usr/bin/bash -o pipefail
# All targets, before and after now have pipefail behaviour.

test5:
    exit 1 | cat
    echo "Will not run"