hello world
#!/bin/bash
echo "hello world"
變量
定義變量：variable_name=variable_value
name="zhangsan"
使用變量：$variable_name
echo $name
替換
echo "name: $name"
只讀狞贱、取消變量
readonly name
unset name
特殊變量
| 變量 | 描述 |
|---|---|
| $0 | 當前腳本的文件名 |
| $n | 第一個參數(shù)是$1菩颖，第二個參數(shù)是$2 |
| $# | 參數(shù)的數(shù)量 |
| $* | All the arguments are double quoted.所有參數(shù) |
| $@ | All the arguments are individually double quoted.所有參數(shù) |
| $? | 上一個命令的退出狀態(tài) |
| $$ | 當前shell的進程號 |
| $! | 最后一個后臺命令的進程號 |
echo "File Name: $0"
echo "First Parameter : $1"
echo "First Parameter : $2"
echo "Quoted Values: $@"
echo "Quoted Values: $*"
echo "Total Number of Parameters : $#"
運算
val=`expr a + b`
記下有以下幾點：
- 運算符和表達式之間必須有空格蚪缀，例如2+2是不正確的赴捞，因為它應該寫成2 + 2作谭。
- ``硼讽，稱為倒逗號之間應包含完整的表達捉偏。
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"
關系運算
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
其他運算符
| 運算符 | 描述 | |
|---|---|---|
| -eq | equal | == |
| -ne | not equal | != |
| -gt | greater than | > |
| -lt | less than | < |
| -ge | greater equal | >= |
| -le | less equal | <= |
| ! | NOT | ! |
| -o | OR | |
| -a | AND | && |
字符串比較
| 運算符 | 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
跳出循環(huán)break、continue
執(zhí)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农渊，默認值
${var:=word} 如果var是null或unset患蹂，默認值，且賦值給var
${var:?message} 如果var為null或unset砸紊，則將消息打印為標準錯誤
${var:+word} 如果var存在传于，默認值
引用
元字符：* ? [ ] ' " $ ; & ( ) | ^ < > new-line space tab
echo "I have $1200" # 無法正確輸出，需要：echo "I have \$1200"
echo 'I have $1200'
輸入輸出重定向
$ echo line 1 > users # 覆蓋之前的數(shù)據(jù)
$ echo line 1 >> users # 追加到之前數(shù)據(jù)后
丟棄輸出：
command > /dev/null
同時放棄輸出和錯誤輸出醉顽，2代表stderr和1代表STDOUT
command > /dev/null 2>&1
pgm > file pgm命令的輸出重定向到file
pgm < file 程序pgm讀取file的輸入
pgm >> file 將pgm命令的輸出追加到file中
| 從一個程序或進程中獲取輸出沼溜，并將其發(fā)送給另一個程序
函數(shù)
# 函數(shù)定義
Hello () {
echo "Hello World $1 $2"
return 10
}
# 方法調用
Hello
# 上一個命令的返回值
ret=$?
echo "Return value is $ret"
