echo 'string1 has a length equal to zero'
else
echo 'string1 has a length greater than zero'
fi
If you execute compare1, you get the following result:
string1 not equal to string2
string2 not equal to string1
string1 is not empty
string2 has a length greater than zero
string1 has a length greater than zero
If two strings are not equal in size, the system pads out the shorter string with trailing spaces for comparison. That is, if the value of string1 is abc and that of string2 is ab, string2 will be padded with a trailing space for comparison purposes — it will have a value of ab.
Number Comparison
The following operators can be used to compare two numbers:
> -eq — To compare whether two numbers are equal
> -ge — To compare whether one number is greater than or equal to the other number
> -le — To compare whether one number is less than or equal to the other number
> -ne — To compare whether two numbers are not equal
> -gt — To compare whether one number is greater than the other number
> -lt — To compare whether one number is less than the other number
The following shell program compares three numbers, number1, number2, and number3:
#!/bin/sh
number1=5
number2=10
number3=5
if [ $number1 -eq $number3 ]; then
echo 'number1 is equal to number3'
else
echo 'number1 is not equal to number3'
fi
if [ $number1 -ne $number2 ]; then
echo 'number1 is not equal to number2'
else
echo 'number1 is equal to number2'
fi
if [ $number1 -gt $number2 ]; then
echo 'number1 is greater than number2'
else
echo 'number1 is not greater than number2'
fi
if [ $number1 -ge $number3 ]; then
echo 'number1 is greater than or equal to number3'
else
echo 'number1 is not greater than or equal to number3'
fi
if [ $number1 -lt $number2 ]; then
echo 'number1 is less than number2'
else
echo 'number1 is not less than number2'
fi
if [ $number1 -le $number3 ]; then
echo 'number1 is less than or equal to number3'
else
echo 'number1 is not less than or equal to number3'
fi
When you execute the shell program, you get the following results:
number1 is equal to number3
number1 is not equal to number2
number1 is not greater than number2
number1 is greater than or equal to number3
number1 is less than number2
number1 is less than or equal to number3
File Operators
The following operators can be used as file comparison operators:
> -d — To ascertain whether a file is a directory
> -f — To ascertain whether a file is a regular file
> -r — To ascertain whether read permission is set for a file
> -s — To ascertain whether a file exists and has a length greater than zero
> -w — To ascertain whether write permission is set for a file
> -x — To ascertain whether execute permission is set for a file
Assume that a shell program called compare3 is in a directory with a file called file1 and a subdirectory dir1 under the current directory. Assume that file1 has a permission of r- x (read and execute permission) and dir1 has a permission of rwx (read, write, and execute permission). The code for the shell program would look like this:
#!/bin/sh
if [ -d $dir1 ]; then
echo 'dir1 is a directory'
