Any interesting uses of Makefiles to share?

Question

\"make\" is not only useful for building your programming project, but it seems to be under-used in other areas.

For example, many shell scripts can be rewritten as

Answer 1

Make's parallelism is particularly handy for shell scripting. Say you want to get the 'uptime' of a whole set of hosts (or basically perform any slow operation). You could do it in a loop:

cat hosts | while read host; do echo "$host: $(ssh $host uptime)"; done

This works, but is slow. You can parallelise this by spawning subshells:

cat hosts | while read host; do (echo "$host: $(ssh $host uptime)")&; done

But now you have no control over how many threads you spawn, and CTRL-C won't cleanly interrupt all threads.

Here is the Make solution: save this to a file (eg. showuptimes) and mark as executable:

#!/usr/bin/make -f

hosts:=$(shell cat)
all: ${hosts}

${hosts} %:
        @echo "$@: `ssh $@ uptime`"

.PHONY: ${hosts} all

Now running cat hosts | ./showuptimes will print the uptimes one by one. cat hosts | ./showuptimes -j will run them all in parallel. The caller has direct control over the degree of parallelisation (-j), or can specify it indirectly by system load (-l).