Shell Loop Loops

1. Cycle
The shell loops and executes a program continuously until the condition is met. Loops are divided into 4 types, while loops, until loops, for fixed processing, for numeric processing.
2. While loop
The while loop is executed until the condition is not met before stopping. Syntax: while [condition]doDo somethingdone example: Loop until user input is correct

#!/bin/bash# desc:while loopwhile ["$yn"! = "Yes"-a "$yn"! = "yes"] do     read-p "Please input yes/yes to stop:" Yndoneecho "OK"

Execution Result:

Example: from 1 to 100

#!/bin/bash# desc:while loopsum=0i=0while [$i-lt]do    i=$ (($i + 1));    

3. Until cycle
Until loops and while instead, the loop is terminated when the condition condition is established. Syntax: until [condition]doDo Somethingdone Example:

#!/bin/bash# desc:while loopuntil ["$yn" = = "Yes"-o "$yn" = = "Yes"]do    read-p "Please input yes/yes to stop:" Y Ndoneecho "OK"

Perform:

[Email protected] sh]$ sh while.sh Please input yes/yes to Stop:hi         

4. For Fixed loop
For is a loop of known number of times. Syntax: for var in con1 Con2. DoDo Somethingdone Example:

#!/bin/bash# desc:for loopfor animal in dog cat pig does    echo "HI, ${animal}" done

Perform:

[[Email protected] sh]$ sh for.sh HI, Doghi, Cathi, pig[[email protected] sh]$

Example: Current catalog file

#!/bin/bash# desc:for loopfilelist=$ (LS) for filename in $filelistdo    echo $filenamedone

5. For-Value loops
For numeric loops, suitable for cyclic numerical calculations. Syntax for (initial value; limit value; step)) doDo Somethingdone Example:

#!/bin/bash# desc:for loopsum=0for ((i=0; i<=100; i++)) do    sum=$ (($sum + $i)) Doneecho ' sum is: ' $sum

Address: http://blog.csdn.net/yonggang7/article/details/40679701

Shell Loop Loops