This script uses sed command to find out all digits or upper characters. -z string (conditional expression) will return true if the length of string is zero.
Script logic
Read one character
[1] Use sed command to determine input character is digit or not (sed -e ‘s/[A-Z]//g’))
[2] Attempt to match regex [0-9] i.e. all digit against the pattern space
[3] If successful, replace that portion matched with replacement // i.e. do nothing.
If digits are in input, it will replace all those digit, and if input is only digit, nothing is left i.e. string is zero and that is what tasted with -z conditional expression.
#!/bin/bash # Shell script to read a character (upper or lower), digit, special symbol and # display message according to the character entered # ----------------------------------------------- # Copyright (c) 2005 nixCraft project <http://cyberciti.biz/fb/> # This script is licensed under GNU GPL version 2.0 or above # ------------------------------------------------------------------------- # This script is part of nixCraft shell script collection (NSSC) # Visit http://bash.cyberciti.biz/ for more information. # ------------------------------------------------------------------------- char="" echo -n "Enter a one character : " read char # use sed command to determine input character is digit or not # -e : start script # s/[0-9]// : Attempt to match regex [0-9] i.e. all digit against the pattern space (echo $char). # If successful, replace that portion matched with replacement i.e. // do nothing. # g : Global replacement # so if digit are in input it will replace all those digit, and if input is only digit, nothing # is left i.e. string is zero and that is what tasted with -z if [ -z $(echo $char | sed -e 's/[0-9]//g') ] then echo "$char is Number/digit" elif [ -z $(echo $char | sed -e 's/[A-Z]//g') ] # find out if character is upper then echo "$char is UPPER character" elif [ -z $(echo $char | sed -e 's/[a-z]//g') ] # find out if character is lower then echo "$char is lower character" else echo "$char is Special symbol" # else it is special character fi