Makeifle: if condition block in define block - if-statement

Question

I create a define block
I'd like to check the program whether in the $PATH env.var,
i.e. whether program exists.
define CheckProgExist
#$(eval exist=$(shell ${1} ${2} 2> /dev/null))
#$(info ${1} ${2})
#$(info ${exist})
ifneq (${exist},"")
#$(error "${1} does not exist in the $${PATH} of env.var")
endif
endef
First Line: #$(eval exist=$(shell ${1} ${2} 2> /dev/null))
Check command exists,
${1} is command I specify
${2} flags of program which I can check if program exists, generally:
return version message (to stdout) if program exists
return null(maybe) if program doesn't exist, because I've redirected stderr to null, output should be null
Second line: #$(info ${1} ${2})
Display argument I input.
Third line: #$(info ${exist})
Display content of variable, if
${1} exists, ${exist} should be message of version and program
${2} does not exists, ${exist} should be empty (or null)
Fourth Line: ifneq (${exist},"")
If variable does not exist, then abort makefile
For example, I'd like to check whether ls exist:
chk_env_hw:
#$(call CheckProgExist,ls,--version)
If program ls does not exist, then error message will display.
But the result seems strange:
>$ make
ls --version
ls (GNU coreutils) 8.32 Copyright (C) 2020 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Written by Richard M. Stallman and David MacKenzie.
Makefile:11: *** "ls does not exist in the ${PATH} of env.var". Stop.
ls is exist but the result shows not.
fully code
define CheckProgExist
#$(eval exist=$(shell ${1} ${2} 2> /dev/null))
#$(info ${1} ${2})
#$(info ${exist})
ifneq (${exist},"")
#$(error "${1} does not exist in the $${PATH} of env.var")
endif
endef
chk_env_hw:
$(call CheckProgExist,ls,--version)

Answer 1

You have several problems here:
ifneq (${exist},"") will fire the error if ${exist} is not equal to "", which is the case. Try ifneq (${exist},).
ls --version sends its output to the standard output, not the standard error, so in your case, with ls --version, exist will not be the empty string. It will be something like ls (GNU coreutils) 8.32...
What you're doing is a strange mixture of make and shell constructs. Make recipes are shell scripts. There is no need to call the shell make function in a recipe. You should maybe try to write a make macro with 100% shell content (including shell variables if you need some). Do not forget to escape the make expansion if needed.
You could try something like (not tested):
define CheckProgExist
#command -v '$(1)' > /dev/null || { echo "$(1) does not exist"; exit 1; }
endef
.PHONY: chk_env_hw
chk_env_hw:
$(call CheckProgExist,ls)
(edited to use command -v as suggested by MadScientist instead of the non-POSIX which).