shell命令行参数的判断 :? 和 :-

${1:?}没有参数就报错return

#!bin/bash
#file name: test1.sh

bar=${1:?param empty}
echo $bar

• 执行bash test1.sh，报错

test1.sh: line 3: 1: param empty

• 执行bash test1.sh hi，输出

hi

${1:-}没有则给默认值

#!bin/bash
#file name: test2.sh

bar1=${1:-}
echo bar1:[$bar1]

bar2=${1:-default value}
echo bar2:[$bar2]

• 执行bash test2.sh，输出

bar1:[]
bar2:[default value]

• 执行bash test1.sh hi，输出

bar1:[hi]
bar2:[hi]