For loop in if cluase.If cluase is not calling

I am new to the Shell,and trying to write few simple scripts.Seems failed here too.Its not invoking if caluse here or not calling for loop.I have shared the o/p

!/bin/bash

set -x read -p "enter Date in DD " d if [$d -gt "00" -a $d -lt "31"] then echo "Choose any one month from given option: Jan,Feb,Mar,Apr,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec" read m for $m in Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec do case "echo $m" in Jan) mnum=01;; Feb) mnum=02;; Mar) mnum=03;; Apr) mnum=04;; May) mnum=05;; Jun) mnum=06;; Jul) mnum=07;; Aug) mnum=08;; Sep) mnum=09;; Oct) mnum=10;; Nov) mnum=11;; Dec) mnum=12;; esac echo "Month is $mnum" done else echo "Its an invalid Date" fi echo "Enter Year in YYYY" read y if echo $y |egrep "^[1|2][0-9][0-9]+$" then echo "Its Valid year" echo "Your date is $d/$m/$y" fi ~ Output: ./a.sh + read -p 'enter Date in DD ' d enter Date in DD 23 + '[23' -gt 00 -a 23 -lt '31]' ./a.sh: line 5: [23: command not found + echo 'Its an invalid Date' Its an invalid Date + echo 'Enter Year in YYYY' Enter Year in YYYY + read y 2015 + echo 2015 + egrep '^[1|2][0-9][0-9]+$' 2015 + echo 'Its Valid year' Its Valid year + echo 'Your date is 23//2015' Your date is 23//2015