The use of regular expressions in the Shell __ regular expressions

Here are two ways to use the shell's regular expressions. use method One:

#赋值给变量var
read var
#定义regex正则表达式
regex= "[0-9]"

if [$var =~ $regex]];then
    #match
    #do Something
fi

For example, to match the input, the requirement must be a number between 0-9:

#读取输入
Read input

regex= "[0-9]"

if [[$input =~ $regex]];then
    echo ' match '
else
    Echo ' Dismatch "
fi

For method One, a regular expression cannot match if it contains an escape character such as "\d". This will be the second way. use method Two:

Read Var
regex= "[A-z]"

if [' Echo $var | grep-p $regex '];then
    echo ' match '
else
    Echo ' Dismatch "
fi

Attention:
-P parameter:
A regular expression parsing using Perl.