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" # abc hello worl
echo 'abc $a' # abc $a
echo "bac $a" # bac hello world
c="today is sunday"
echo "hello,$c" # hello,$c
echo 'hello,$c' # hello,today is sunday
echo $ddd
a="hello"
echo $a_1
echo $a _1 # hello _1
echo ${a}_1 # hello_1
b="sunday"
ehco ${b}
pwd
$PWD
echo $PWD # /home/16116374
echo $USER # 16116374
echo $path #
echo $PATH # /usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/16116374/.local/bin:/home/16116374/bin:/home/16116374/test:/home/16116374
echo $home #
echo $HOME # /home/16116374
a=1
b=(1 2 3 4 5)
echo $a # 1
echo $b # 1
echo ${a[*]} # 1
echo ${b[*]} # 1 2 3 4 5
echo ${b[4]} # 5
echo ${#b[*]} # 5 （元组长度）
which python # /usr/bin/python
which 1.sh
ls
which file.out
a=`ls`
echo $a
ls
array=(`ls`)
echo "print(3*7)" | python # 21
echo $array
echo ${array[*]}
echo ${#array[*]}
echo ${array[6]}
echo ${array[-1]}
echo "a
bbb" # a
bbb
echo -e "a
bbbb"
# a
bbbb ( 为换行符)
echo "a\"bbbb" # abb
echo my dir is `ls` # my dir is 1 1000.sh 14 1.html 1.sh 3 5 a aaa.sh baidu.keyword calc.sh -cookie employee.txt
echo my dir is ${ls} # my dir is
echo my dir is $(ls) # my dir is 1 1000.sh 14 1.html 1.sh 3 5 a aaa.sh baidu.keyword calc.sh -cookie employee.txt
a=4;b=7
echo $((a+b)) # 11
echo $(($a+$b)) # 11
echo $((a-b)) # -3
echo $(3+2) # -bash: 3+2: command not found
echo $((3+5)) # 8
a=4;b=2;c=3
echo $((a+b*c)) # 10
a="hello world is a happy day"
echo $a # hello world is a happy day
echo hello world luming com # hello world luming com
a=33444
echo $a # 33444
echo $((a+2)) # 33446
echo $((4+a)) # 33448
echo $((a/4)) # 8361
echo $((a*6)) # 200664
a=5
((a=a+5))
echo $a # 10
((a=a*6))
echo $a # 60
((a++));echo $a # 61
((a--));echo $a #60
a=4;b=6
((a<b))
echo $? # 0
((a>b))
echo $? # 1
echo $((2/3)) # 0
echo $((3/2)) # 1
awk 'BEGIN{print 2/3}' 除数支持浮点数据 # 1.5
s="hello from china"
echo $s
echo ${s}
echo ${s:6} # from china
echo ${s:6:3} # fro
echo ${s:6:5} # from
echo ${#s} # 16
echo ${s#hello} # from china
echo $s # hello from china
echo "${s#china}"
echo "${s#chinaa}"
echo "${s#ccc}"
echo "${s#*m}"
echo "${s#*l}" # lo from china
echo "${s#*a}" #
echo "${s#*n}" # a
echo "${s#*o}" *放在前面 # from china
echo "${s##*o}" 贪婪匹配，匹配至最后一个（掐头） # m china
echo "${s%na}" 去尾 # hello from chi
echo "${s%h*}" *放在后面 # hello from c
echo "${s%%o*}" 贪婪匹配 # hell
echo "${s/china/shanghai}" china为被替换的内容，shanghai为替换的内容 # hello from shanghai
echo -e "1|2|3 4|5|6 7|8|9" 输出的结果为：
1|2|3
4|5|6
7|8|9