Shell: Shell Process Control details, shell Process Control details

Shell: Shell Process Control details, shell Process Control details
Shell: Shell Process Control details if else

If statement

Syntax:

if conditionthen    command    ...fi

Eg:

#!/bin/basha=100b=100if [ $a == $b ]then    echo "$a == $b"fi

Output:

100 == 100

You can also write a line in the terminal:

[zhang@localhost ~]$ a=100[zhang@localhost ~]$ b=100[zhang@localhost ~]$ if [ $a == $b ]; then    echo "$a == $b"; fi100 == 100

If else statement

Syntax:

if conditionthen    command    ...else    command    ...fi

Eg:

Enter

[zhang@localhost ~]$ a=100[zhang@localhost ~]$ b=200[zhang@localhost ~]$ if [ $a == $b ]> then>     echo "$a == $b"> else>     echo "$a != $b"> fi100 != 200

If elif else statement

Syntax:

if condition1then    command1    ...elif comdition2then    command2else    commandfi

Eg:

#!/bin/basha=100b=200c=150if [ $[a + c] > $b ]then    echo "$a + $c > $b  return true"elif [ $[a + c] < $b ]then     echo "$a + $c < $b  return true"else    echo "$a + $c = $b  return true"fi

Output result:

100 + 150 > 200  return true

For Loop

For Syntax:

for var in item1 item2 ... itemndo    command1    command2    ...    commandndone

Write a line:

for var in item1 item2 ... itemn; do command1;command2 ... done;

Eg:

[zhang@localhost ~]$ for num in 1 2 4 8 16> do>     echo $num> done124816

One row:

[zhang@localhost ~]$ for num in 1 2 3 4 5; do echo $num; done12345

While statement

While Syntax:

while conditiondo    commanddone

Eg:

#!/bin/bashnum=1while(($num<=5))do    echo $num    let "num++"done

Output result:

12345

Infinite Loop

while :do    commanddone

Or

while truedo    commanddone

Or

for (( ; ; ))

Until Loop

Until Syntax:

until condiiondo    commanddone

Generally, while is used as an alternative.

Case

Case Syntax:

case value invalue1)    command1    command2    ...    commandn    ;;value2)    command1    command2    ...    commandn    ;;value3)    command1    command2    ...    commandn    ;;*)    command1    command2    ...    commandn    ;;esac

;: All commands are executed. It is equivalent to break.

*: It is equivalent to default in java.

Eg:

#!/bin/bashvalue=2case $value in1)    echo "$value equal 1"    ;;2)    echo "$value equal 2"    ;;3)    echo "$value equal 3"    ;;*)    echo "$value not find"    ;;esac

Output result:

2 equal 2

Skip Loop

Break command

#!/bin/bashfor i in 1 2 3 4 5do   if [ $[i % 2] == 0 ]   then        echo "$i"        break   fidone

Output: 2

Continue command

#!/bin/bashfor i in 1 2 3 4 5do    if [ $[i % 2] == 0 ]    then        echo "$i"        continue     fidone

Output:

24

Esac command

Used Together with case as the end symbol of case.