How the shell determines if the variable entered by the user from the keyboard is a number

There is no direct command in the bash shell to determine whether a variable is a pure number, then we are using an indirect method:

Problem Description:

Read-t 30-p "Please a number:" NUM

Use the Read command to accept the user from the keyboard input a variable, stored in the variable num, sometimes the user blindly input a pass, or do not input, this will affect the execution of the script, Gu judge beforehand, better is also necessary, then how to judge?

Method One:

To further process num variables:

String= ' echo ${num}|sed ' ss^.*[0-9] $SS ' give ${num to the SED command to process, replace any number at the beginning of any number with an empty, and then deal with the result of the substitution. That

${string} is empty then ${num} is a pure number, otherwise it is not a pure number ...

Example Demo:

#!/bin/bash

Read-t 10-p "Please input a number:" NUM

String= ' echo ${num} |sed ' ss^[0-9].* $SS '

[[-Z ${string}]] && echo true | | echo False

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EXECUTE as follows:

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Method Two: Also recommended is a

Match ${num} to digital mode i.e. =~^[0-9]+$

Example Demo:

#!/bin/bash

Read-t 10-p "Please input a number:" NUM

[[${num} =~ ^[0-9]+$]] && echo true | | echo False

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Execution Result:

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This article from the "Linux-related technology" blog, declined to reprint!

How the shell determines if the variable entered by the user from the keyboard is a number