How to use if in shell

Syntax

if [ expression ]
then
  commands
elif [ expression ]
then
  commands
else
  commands
fi

Number check

Operator	Meaning
-eq	equal
-ne	not equal
-gt	greater than
-ge	greater than or equal
-lt	less than
-le	less than or equal

String check

Operator	Meaning
-z	empty
-n	not empty
=	equal
!=	not equal

File check

Operator	Meaning
-e	exist
-f	file
-d	directory
-r	readable
-w	writable
-x	executable
-s	size > 0
-c	char file
-b	block file