bash to test if command can run

Question

I have the following makefile:

SHELL += -eu
GREEN=$(shell echo -e "\033[0;32m")
RED=$(shell echo -e "\033[0;31m")

AWS=$(shell command aws --version 2> /dev/null)
all: prereqs
    @echo "${GREEN} ✓ Testing our local environment for dependencies."

prereqs:
    ifndef "${AWS}"
        $(error "${RED} AWS is not available please install aws-cli")
    endif
        "${AWS}"

How do I change it so that if there is dependancy missing to show a more appropriate error and continue with the check?

I tried:

prereqs:
    aws --version || $(error "${RED} AWS is not available please install aws-cli")
    @echo

But it does not seem to be working, what am I missing as aws exists!

Any advice is much appreciated.

This isn't bash, it's sh. Make doesn't use bash unless it's told to. Correct your tagging. — Charles Duffy
– Charles Duffy, Commented Nov 26, 2016 at 19:37
(that said, it's sh with some non-POSIX-compliant extensions -- echo -e isn't allowed to do anything other than print -e on output by the letter of the standard; see in particularly the APPLICATION USAGE section showing how to use printf '%b\n' instead). — Charles Duffy
– Charles Duffy, Commented Nov 26, 2016 at 19:38
...for a case in point (assuming that /bin/sh is provided by bash running in POSIX mode on your system), see how your makefile behaves if run after export BASHOPTS=xpg_echo — Charles Duffy
– Charles Duffy, Commented Nov 26, 2016 at 19:43

Mike Kinghan · Accepted Answer · 2016-11-26 19:18:47Z

1

You're missing a couple of points of knowledge about how make works:-

Write this instead:

SHELL += -eu
GREEN=$(shell echo -e "\033[0;32m")
RED=$(shell echo -e "\033[0;31m")

AWS:=$(shell command aws --version 2> /dev/null)
all: prereqs
    @echo "${GREEN} ✓ Testing our local environment for dependencies."

prereqs:
ifndef AWS
$(error "${RED} AWS is not available please install aws-cli")
endif
    @echo "${AWS}"

and note the differences.

I also think an improvement would be:

SHELL += -eu
GREEN=$(shell echo -e "\033[0;32m")
RED=$(shell echo -e "\033[0;31m")

AWS:=$(shell command aws --version 2> /dev/null)
$(info ${GREEN} ✓ Testing our local environment for dependencies.)
all: prereqs

prereqs:
ifndef AWS
$(error "${RED} AWS is not available please install aws-cli")
endif
    @echo "${AWS}"

as well not leaving the user in a coloured shell.

answered Nov 26, 2016 at 19:18

Mike Kinghan

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2 Comments

Charles Duffy Over a year ago

grumbles a bit about keeping the OP's non-POSIX-compliant echo -e usage, vs converting to printf '%b' "\033[0;32m" or such

MadScientist Over a year ago

Also, leaving the ifndef in the context of the prereqs target is misleading: people might think it's only run when the prereqs target is run which is not true, it's run when the makefile is parsed. I recommend putting it up just after the info and before the all target so it's more clear what actually happens.

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