Shell Script Computation and Comaprision

Comparison

Unlike other scripting language shell script has provided different methods to compare string and numbers.

1. Numeric Comparison Syntax : test Number1 option Number2 Test command will return the true of false based on the opration performed between two numbers Different options are as below:

· -ne means Not Equal to · -lt means Less Then · -le means Less Then or Equal to · -gt means Greater Then · -ge means Greater Then or Equal to

Example:

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a=10 b=20

test $a –eq $b # will return False test $a –lt $b # will return True

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2. String Compression String comparison done with the simple mathematical operator Syntax: test string1 option string2 or test option string Different options are as below:

· = = means Equal to · != means Not Equal to · -n means Not NULL ( unary operator ) · -z means NULL ( unary operator )

Example:

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Test “Gaurang” == “Gaurang” # this will return True A=”string “ Test -z “$A” # will Return false as A is not NULL

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Note: Remember if you are compring strings and the strings are assigned in some variables you need to put that variables in the double quotes ( “$str” ), other wise it will give you error.

Computation

In the shell script you can’t directly add the two numbers as follows A=1 + 1 # this will gives you error

There is a special command called expr that is used for the normal integer computation. Syntax: expr num1 operator num2 Example:

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a=2 b=3

c=`expr $a + $b` echo $c # will print 5, summation of 2 and 3

c= `expr $b / $a` echo $c #will print 1, as expr returns only integer value c= `expr $a * $b` # will gives you error, # asterisk ( * ) has some other special meaning

c=`expr $a \* $b` # correct way to multiply the value

echo $c # will print 6

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