Shell Scripting Learning 20 shell until loop

Source: Internet
Author: User

The Until loop executes a series of commands until the condition is true. The Until loop and the while loop are just the opposite of the processing mode. The general while loop is better than the until loop, but at some point it is only rare that the until loop is more useful.

The Until loop format is:

Until Commanddo   Statement (s) to being executed until command is Truedone

The command is usually a conditional expression, and if the return value is false, the statement in the loop body continues to execute, otherwise it jumps out of the loop.

For example, use the until command to output a number from 0 to 9:

    1. #!/bin/bash
    2. A=0
    3. Until [ ! $a -lt ]
    4. Do
    5. echo $a
    6. a= ' expr $a + 1 '
    7. Done

Operation Result:


Shell Scripting Learning 20 shell until loop

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