Shell Script Programming Loop statements

Repeating a series of commands while running a script is common, and we need to use loop statements to do this.

One, for command

Format: for variable in list;

Loop body

Done

The for command iterates through each value in the list and exits the loop after the traversal is complete.

There are several forms of the list:

1, a series of values defined in the command;

2, variables;

3, order;

4, directory;

5, documents.

Example 1:

650) this.width=650; "title=" 1451812909445180.jpg "alt=" 1.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20160103/1451812909445180.jpg "/>

650) this.width=650; "style=" text-align:center; "title=" 1451834452379687.jpg "alt=" 1.jpg "src=" http:// Www.178linux.com/ueditor/php/upload/image/20160103/1451834452379687.jpg "/>

In the example above, use the {initial value: End value} format to represent the numeric value of an interval.

Example 2: Use a variable as a list:

650) this.width=650; "title=" 1451813025841146.jpg "alt=" 2.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20160103/1451813025841146.jpg "/>

Example 3: Generate a list with a command:

650) this.width=650; "title=" 1451834846978770.jpg "alt=" 2.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20160103/1451834846978770.jpg "/>

In the previous example, using the SEQ command to generate the list, the SEQ command is in the format: SEQ [initial value step] terminating value

650) this.width=650; "title=" 1451813301230401.jpg "alt=" 3.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20160103/1451813301230401.jpg "/>

The above two examples use anti-quotes to get the result of the command run.

Example 4: Use the directory as a list:

650) this.width=650; "title=" 1451834311885880.jpg "alt=" 4.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20160103/1451834311885880.jpg "/>

Second, C language style for command

Format: for (variable assignment; loop termination condition; step)); Do

Loop body

Done

Example: for 1 plus to 100 and:

650) this.width=650; "title=" 1451835193946183.jpg "alt=" 5.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20160103/1451835193946183.jpg "/>

Iii. until order

Format: Until condition; Do

Statement

...

Done

When a condition in the until command is satisfied, the loop exits.

Instance:

650) this.width=650; "title=" 1451835795903908.jpg "alt=" 6.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20160103/1451835795903908.jpg "/>

Four. While command

Format: While condition; Do

Statement

...

Done

The while command enters the loop when the condition is met.

Instance:

650) this.width=650; "title=" 1451835996609630.jpg "alt=" 7.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20160103/1451835996609630.jpg "/>

V. Control cycle

1. Break command

function: Exits a loop that is in progress.

Instance: Exits the loop if the variable i is 3.

650) this.width=650; "title=" 1451837151654175.jpg "alt=" 1.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20160104/1451837151654175.jpg "/>

2. Continue command

Function: Advance into the next round of circulation.

Example: Add a number from 1 to 20 and 51 to 100:

650) this.width=650; "title=" 1451837327444231.jpg "alt=" 2.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20160104/1451837327444231.jpg "/>

Vi. the use of the while

1. Dead Cycle

Format: while:; Do

Statement

Done

Instance:

650) this.width=650; "title=" 1451838566432871.jpg "alt=" 1.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20160104/1451838566432871.jpg "/>

2. Read the contents of the file into the loop by line

Format: while read variable name; Do

Loop body

Done < files

Example: Read the contents of the/etc/passwd file line by row:

650) this.width=650; "title=" 1451839645380871.jpg "alt=" 2.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20160104/1451839645380871.jpg "/>

Shell Script Programming Loop statements