bash的测试，如果命令可以运行

Question

我有以下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}" 

我如何改变它，这样如果有扶养缺少展现一个更合适的错误，并继续检查？

我想：

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

但它似乎并不奏效，我失去了什么为aws存在！

任何意见是非常感谢。

Answer 1

你错过了几个知识点的有关如何make作品： -

• The difference between recursively expanded and simply expanded variables
• The syntax of ifdef

写这个：

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}" 

，并注意差异。

我也觉得一个改进是：

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}" 

也不会离开的彩色外壳的用户。