Shell script - 2

Shell script - 2
To go to Shell script Session click here
To go to UNIX basic commands click here

Its time to learn operators

 Arithmetic Operator:

           

Symbol	Meaning
+	Addition
-	Minus(subtract)
*	Multiply
/	Divide
%	Modulus
=	Assignment
==	Equal to
!=	Not equal to

In the above the three given in red will be used with comparison and others will be used with expr.

Relation Operators/Comparative operators for numbers/integers:

Operator	Meaning	Usage Example
-eq	Equality condition	[$a –eq $b]
-ne	Not equal condition	[$a –ne $b]
-gt	Greater than condition	[$a –gt $b]
-lt	Less than Condition	[$a –lt $b]
-ge	Greater than equal to condition	[$a –ge $b]
-le	Lesser than equal to condition	[$a –le $b]

Boolean Operators:

Symbol/operator	Meaning	Usage Example
!	Not/Negation	[! [$a –eq $b]] if[$a –eq $b] evaluates to true ! ll make it false and vice versa
-o	OR	[ [$a –eq $b ] –o [-a –eq $c] that is any one condition need to be true
-a	AND	[ [$a –eq $b ] –a [-a –eq $c] that is both condition should be true

Operators used with Strings

Symbol/Operator	Meaning	Usage Example
=	Checks if both strings are equal	[ $str1 = $str2 ]
!=	Checks if both strings are not equal	[ $str1 != $str2 ]
-z	Checks for length is zero	[ $str1 –z $str2 ]
-n	Checks for length is not zero	[ $str1 –n $str2 ]

Files Operators

Symbol/Operator	Meaning	Usage Example
-b file	Checks if the file is block special file	[ -b $filename ]
-c file	Checks if the files is char special file	[ -c $filename ]
-d file	Checks if the file is directory	[ -d $filename ]
-e file	Check for file existence	[ -e $filename ]
-f file	Check if the file is ordinary file	[ -f $filename ]
-g file	Check if the file group id is set	[ -g $filename ]
-p file	Check if the file is a named pipe	[ -p $filename ]
-t file	Check if the file descriptor is open	[ -t $filename ]
-u file	Checks if the files set user id is set	[ -u $filename ]
-r file	Checks if the file is readable	[ -r $filename ]
-s file	Checks if the file size is greater than 0	[ -s $filename ]
-w file	Checks if the file is writable	[ -w $filename ]
-x file	Checks if the file is Executable	[ -x $filename ]

Example 6:

#!/bin/sh

filename=$1

if [-r filename] then

echo "file is readable"

elif [-x filename] then

echo "file is executable"

elif [-w filename] then

echo "file is writable"

else

echo "ERRROR: $filename HAS PERMISSION PROB"

fi

To go to next session click here don't forget to put your feed back as comments which encourages me to do this and you can also post your questions or solve/give answers for others questions, Thanks in advance friends.....