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Editor to share with you how to use the circular sentence of shell scripting programming, I believe most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to know it!

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

1. For command

Format: for variable in list; do

Cyclic body

Done

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

The list has the following forms:

1. A series of values defined in the command

2. Variables

3. Command

4. Catalogue

5. Documents.

Example 1:

In the example above, {initial value is used. The ending value} format to represent the numerical value of an interval.

Example 2: use variables as a list:

Example 3: generate a list with the command:

In the above example, the seq command is used to generate the list. The format of the seq command is: seq [initial value step] termination value.

Using backquotes in the above two examples will get the result of the command running.

Example 4: use the directory as a list:

II. For commands in C language style

Format: for ((variable assignment; Loop termination condition; step size); do

Cyclic body

Done

Example: add the sum from 1 to 100:

3. Until command

Format: until condition; do

Statement

...

Done

The loop exits when the conditions in the until command are met.

Example:

4. While command

Format: while condition; do

Statement

...

Done

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

Example:

V. Control cycle

1. Break command

Function: exit a loop in progress.

Example: exit the loop if the variable I is 3.

2. Continue command

Function: enter the next cycle ahead of time.

Example: add the numbers between 1 to 20 and 51 to 100:

VI. Special usage of while

1. Endless cycle

Format: while:; do

Statement

Done

Example:

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

Format: while read variable name; do

Cyclic body

Done < file

Example: read the contents of / etc/passwd file line by line:

The above is all the contents of this article entitled "how to use cyclic statements in shell scripting programming". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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