Shell finishing (29) = = = Determines whether the user input can be used as a variable

(a) Title:

Accept a user input to determine if the input can be used as a variable

Conditions that can be used as variables

(1) Uppercase and lowercase letters can be

(2) A number may be in the middle of the letter, but cannot begin with a number

(3) Special characters except "_" can not be used as variables

For example:

[Email protected] hushuai]# bash 22.sh

Input:1dsf

Name is not

[Email protected] hushuai]# bash 22.sh

Input:=ewr

Name is not

[Email protected] hushuai]# bash 22.sh

Input:_

Name is OK

[Email protected] hushuai]# bash 22.sh

Input:_123

Name is OK

[Email protected] hushuai]#

The shell code is as follows:

Version 1:

#!/bin/bash

Read-p "Input:" A

B= ' echo $a | Sed-r ' s/[a-za-z0-9_]/a/g ' |grep-o ' a ' |wc-l '

C=${#a}

D= ' echo $a |cut-c1 '

echo $d | grep ' [0-9] ' &>/dev/null

If [$?-eq 0];then

echo $a is not && exit 0

Fi

If [$c-eq $b];then

echo $a is ok

Else

Echo $a is not

Fi

Version of a replacement after the number of statistics, it is troublesome, we directly replace the empty is not good? Revisions on the basis of version (i)

Version (b)

The shell code is as follows:

#!/bin/bash

Read-p "Input:" A

D= ' echo $a |cut-c1 '

echo $d | grep ' [0-9] ' &>/dev/null

If [$?-eq 0];then

echo $a is not && exit 0

Fi

B= ' echo $a | Sed-r ' s/[a-za-z_0-9]//g '

If [-Z $b];then

echo $a is ok

Else

Echo $a is not

Fi

This is a method because the writing of the regular, so it is relatively simple, in fact, we can also be a letter a letter to compare

Example: Version (c)

The shell code is as follows:

#!/bin/bash

Read-p "Plz Input A Name:" N

s=${#n}

Start= ' echo $n |cut-c1 '

Check= ' echo $start | Grep-c ' [A-za-z_] '

If [$check-ne 1];then

echo "Name not OK" && exit 1

Fi

For i in ' seq 2 $s '

Do

Xxoo= ' echo $n |cut-c $i '

Check= ' echo $xxoo | Grep-c ' [a-za-z_0-9] '

If [$check-ne 1];then

echo "Name not OK" && exit 1

Fi

Done

echo "Name is OK"

All of the above just provides a way of thinking and learning to study more on a problem, in fact, if you know an order, there is another way.

Command: eval

Version (iv):

#!/bin/bash

Read-p "Input:" N

Eval $n =1 &>/dev/null

If [$?-eq 0];then

echo "Name is OK"

Else

echo "Name is not"

Fi

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Shell finishing (29) = = = Determines whether the user input can be used as a variable