shell脚本中要加空格“./test.sh: line 17: [12: command not found”

一个简单的shell脚本：
#!/bin/bash
echo "input1:"
read FIRST
echo "input2:"
read SECOND
if ["$FIRST" -gt "$SECOND"]    ------修改为 if [   "$FIRST" -gt "$SECOND"   ] 
 then
  echo "$FIRST is greater than $SECOND"
fi

执行：
[root@localhost shell]# ./test.sh 
input1:
12
input2:
10
./test.sh: line 17: [12: command not found
报错，见上面红色行

====
最后找到原因，原来是少了两个空格闹的
把if ["$FIRST" -gt "$SECOND"]    ------修改为 if [   "$FIRST" -gt "$SECOND"   ] ，程序正确不再报错了