hello world
#!/bin/bash
echo "hello world"
变量
定义变量：variable_name=variable_value
name="zhangsan"
使用变量：$variable_name
echo $name
替换
echo "name: $name"
只读、取消变量
readonly name
unset name
特殊变量
| 变量 | 描述 |
|---|---|
| $0 | 当前脚本的文件名 |
| $n | 第一个参数是$1，第二个参数是$2 |
| $# | 参数的数量 |
| $* | All the arguments are double quoted.所有参数 |
| $@ | All the arguments are individually double quoted.所有参数 |
| $? | 上一个命令的退出状态 |
| $$ | 当前shell的进程号 |
| $! | 最后一个后台命令的进程号 |
echo "File Name: $0"
echo "First Parameter : $1"
echo "First Parameter : $2"
echo "Quoted Values: $@"
echo "Quoted Values: $*"
echo "Total Number of Parameters : $#"
运算
val=`expr a + b`
记下有以下几点：
- 运算符和表达式之间必须有空格，例如2+2是不正确的，因为它应该写成2 + 2。
- ``，称为倒逗号之间应包含完整的表达。
a=10
b=20
val=`expr $a + $b`
echo "a + b : $val"
val=`expr $a - $b`
echo "a - b : $val"
val=`expr $a * $b`
echo "a * b : $val"
val=`expr $b / $a`
echo "b / a : $val"
val=`expr $b % $a`
echo "b % a : $val"
关系运算
if [ $a -eq $b ]
then
echo "$a -eq $b : a is equal to b"
else
echo "$a -eq $b: a is not equal to b"
fi
其他运算符
| 运算符 | 描述 | |
|---|---|---|
| -eq | equal | == |
| -ne | not equal | != |
| -gt | greater than | > |
| -lt | less than | < |
| -ge | greater equal | >= |
| -le | less equal | <= |
| ! | NOT | ! |
| -o | OR | |
| -a | AND | && |
字符串比较
| 运算符 | 描述 |
|---|---|
| $a = $b | "$a = $b : a is equal to b" |
| $a != $b | "$a != $b : a is not equal to b" |
| -z "$a" | "-z $a : string length is zero" |
| -n "$a" | "-n $a : string length is not zero" |
| $a | "$a : string is not empty" |
if
a=10
b=20
if [ $a == $b ]
then
echo "a is equal to b"
elif [ $a -gt $b ]
then
echo "a is greater than b"
elif [ $a -lt $b ]
then
echo "a is less than b"
else
echo "None of the condition met"
fi
case
FRUIT="kiwi"
case "$FRUIT" in
"apple") echo "Apple pie is quite tasty."
;;
"banana") echo "I like banana nut bread."
;;
"kiwi") echo "New Zealand is famous for kiwi."
;;
esac
while
a=0
while [ $a -lt 10 ]
do
echo $a
a=`expr $a + 1`
done
for
for var in 0 1 2 3 4 5 6 7 8 9
do
echo $var
done
until
a=0
until [ ! $a -lt 10 ]; do
a=`expr $a + 1`
echo $a
done
跳出循环break、continue
执行命令：command
DATE=`date`
echo "Date is $DATE"
USERS=`who | wc -l`
echo "Logged in user are $USERS"
${var}等同$var
${var:-word} 如果var是null或unset，默认值
${var:=word} 如果var是null或unset，默认值，且赋值给var
${var:?message} 如果var为null或unset，则将消息打印为标准错误
${var:+word} 如果var存在，默认值
引用
元字符：* ? [ ] ' " $ ; & ( ) | ^ < > new-line space tab
echo "I have $1200" # 无法正确输出，需要：echo "I have \$1200"
echo 'I have $1200'
输入输出重定向
$ echo line 1 > users # 覆盖之前的数据
$ echo line 1 >> users # 追加到之前数据后
丢弃输出：
command > /dev/null
同时放弃输出和错误输出，2代表stderr和1代表STDOUT
command > /dev/null 2>&1
pgm > file pgm命令的输出重定向到file
pgm < file 程序pgm读取file的输入
pgm >> file 将pgm命令的输出追加到file中
| 从一个程序或进程中获取输出，并将其发送给另一个程序
函数
# 函数定义
Hello () {
echo "Hello World $1 $2"
return 10
}
# 方法调用
Hello
# 上一个命令的返回值
ret=$?
echo "Return value is $ret"
