If / else statements on bash script

An overview of if/else statements in Bash scripts and comparison conditions Bash provides the following forms of if/else statements:

1. Using if for a basic comparison

   if [ condition ]
   then
   ...
   fi

2. Using if and else for comparisons

   if [ condition ]
   then
   ...
   else
   ...
   fi

3. Using if, elif (else if), and else for comparisons

   if [ condition ]
   then
   ...
   elif [ condition ]
   then
   ...
   else
   ...
   fi

Conditions can test many things. The available comparisons are summarized below.

String comparison operations

String Comparison	Description
Str1 == Str2	Returns true if the strings are equal
Str1 != Str2	Returns true if the strings are not equal
-n Str1	Returns true if the string is not null
-z Str1	Returns true if the string is null

Numeric comparison operations

Numeric Comparison	Description
expr1 -eq expr2	Returns true if the expressions are equal
expr1-ne expr2	Returns true if the expressions are not equal
expr1 -gt expr2	Returns true if expr1 is greater than expr2
expr1 -ge expr2	Returns true if expr1 is greater than or equal to expr2
expr1 -lt expr2	Returns true if expr1 is less than expr2
expr1 -le expr2	Returns true if expr1 is less than or equal to expr2
expr1 -a expr2	True if both expr1 and expr2 are true.
expr1 -o expr2	True if either expr1 or expr2 is true.
! expr1	Negates the result of the expression

File test operations

File Conditionals	Description
-d dir	True if the file is a directory
-e file -a file	True if the file exists (note that this is not particularly portable, thus -f is generally used)
-f file	True if the provided string is a file
-g file	True if the group id is set on a file
-k file	True if file exists and “sticky” bit is set
-r file	True if the file is readable
-s file	True if the file has a non-zero size (size greater than zero)
-b file	True if file exists and is a block special file
-c file	True if file exists and is a character special file
-p file	True if file exists and is a named pipe (FIFO)
-t [fd]	True if file descriptor fd is open and refers to a terminal. If fd is omitted, it defaults to 1 (standard output).
-u file	True if the user id is set on a file
-w file	True if the file is writable
-x file	True if the file is an executable
-O file	True if file exists and is owned by the effective user id
-G file	True if file exists and is owned by the effective group id
-L file	True if file exists and is a symbolic link
-S file	True if file exists and is a socket.
-N file	True if file exists and has been modified since it was last read.
FILE1 -nt FILE2	True if FILE1 has been changed more recently than FILE2, or if FILE1 exists and FILE2 does not.
FILE1 -ot FILE2	True if FILE1 is older than FILE2, or if FILE2 exists and FILE1 does not.
FILE1 -ef FILE2	True if FILE1 and FILE2 refer to the same device and inode numbers.