6 ways to determine if a string is a number in the shell share the _linux shell

This article mainly introduces the "shell judge string is a number", mainly related to the shell to determine whether the string is a digital content, for the shell to determine whether the number of figures interested students can refer to.

#!/bin/bash # # method 1 A=1234;echo "$a" | [-N ' ' sed-n '/^[0-9][0-9]*$/p '] && echo string A is numbers the first-n is the test flag of the shell, to the back string "' Sed-n '/^[0-9][0-9]*$/
   P ' "To test, if not NULL, the result is true.
  SED defaults to display all input line information, the SED "-n" option is to let sed not display, but only to show what we need: that is, the following expression matches the row, this is done by adding the "P" command in the expression.  
/^[0-9][0-9]*$/his meaning is to match at least one digit line # # method 2, yes, but not bash implementation, is using GREP's regular #if grep ' ^[[:d igit:]]*$ ' <<< '; then 
# echo ' is number. ' 
#else # echo ' No. ' #fi # # Method 3 #if ["-GT 0] 2>/dev/null; then # echo" is number. " 
#else # echo ' No. ' #fi # # method 4,case #case "in # [1-9][0-9]*] # echo" is number. " 
#    ;; 
#  *)  
#    ;; #esac # # Method 5,awk #echo $1| awk ' {print ($0~/^[-]? ( [0-9]) +[.]? ([0-9]) +$/)? " Number ":" String "} ' # # method 5,awk #if [-N ' $ (echo $1| 
Sed-n "/^[0-9]\+$/p") "];then # echo" is number. #else # echo ' No. ' #fi # # method 6,expr Expr $ "+" &>/dev/null if [$?-eq 0];then echo "is Numbe R "Else echo" not Number "fi