a=ddd
?echo $a
?echo a
echo $p
?echo $PATH
?which find
which adb
echo $PATH
[ 2 -gt 1 ]
?echo $?
?ls
?a=1
?echo $a
?b=hello world
?b="hello world"
?echo $b
?echo b
?a=‘hello world‘
?a
?echo $a
?b=1
?echo "abc $a"
?echo ‘abc $a‘
?echo "bac $a"
?c="today is sunday"
?echo "hello,$c"
?echo ‘hello,$c‘
?echo $ddd
?a="hello"
?echo $a_1
?echo $a _1
?echo ${a}_1
?b="sunday"
?ehco ${b}
?echo ${b}
?pwd
?$PWD
?echo $PWD
?echo $USER
?echo $path
?echo $PATH
?echo $home
?echo $HOME
?a=1
?b=(1 2 3 4 5)
?echo $a
?echo $b
?echo ${a[*]}
?echo ${b[*]}
?echo ${b[4]}
?echo ${#b[*]}
?which python
?which 1.sh
?ls
?which file.out
?a=`ls`
?echo $a
?ls
?array=(`ls`)
?echo $array
?echo ${array[*]}
?echo ${#array[*]}
?echo ${array[6]}
?echo ${array[-1]}
?echo "anbbb"
?echo -e "anbbbb"
?echo "a"bbbb"
?my dir is `ls`
?echo my dir is `ls`
?echo my dir is ${ls}
?echo my dir is $(ls)
a=4;b=7echo $((a+b))?echo $(($a+$b))?echo $((a-b))?echo $(3+2)?echo $((3+5))?a=4;b=2;c=3?echo $((a+b*c))?a="hello world is a happy day"?echo $a?echo hello world luming com?a=33444?echo $a?echo $((a+2))?echo $((4+a))?echo $((a/4))?echo $((a*6))?a=5?((a=a+5))?echo $a?((a=a*6))?echo $a?((a++));echo $a?((a--));echo $a?a=4;b=6?((a<b))?echo $??((a>b))?echo $??echo $((2/3))?echo $((3/2))?awk ‘BEGIN{print 2/3}‘ 支持字符串