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How to understand the while sentence in Shell, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

The while loop is used to execute a series of commands continuously, as well as to read data from an input file; commands are usually test conditions.

The while loop format is:

While conditiondo commanddone

The following is a basic while loop, and the test condition is: if int is less than or equal to 5, then the condition returns true. Int starts at 0, and int is added by 1 each time the cycle is processed. Run the above script, return the numbers 1 to 5, and then terminate.

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

Run the script and output:

12345

The above example uses the Bash let command, which is used to execute one or more expressions. There is no need to add $to represent the variable in the variable calculation. For more information, please see: Bash let command

.

The while loop can be used to read keyboard information. In the following example, the input information is set to the variable FILM and press to end the loop.

Echo 'Press exit' echo-n 'enter the name of your favorite website:' while read FILMdo echo 'Yes! $FILM is a good website "done"

Run the script with output similar to the following:

Press exit to enter the name of your favorite website: rookie tutorial yes! The rookie tutorial is a good website.

Infinite cycle

Infinite loop syntax format:

While: do commanddone

Or

While truedo commanddone

Or

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