Test Command in Linux

Test command is used to check the condition is true or not. To test a condition use test or [ ] as explained below.

Syntax of test command

if test condition then statement fi

or

if [ condition ] then statement fi

Note that you must put space between braces [ ] to test a condition.

Test Condition Types

1.   Arithmetic Comparison

−eq	Equal to
−ne	Not equal to
−gt	Greater than
−ge	Greater than or equal
−lt	Less than
−le	Less than or equal
!	not

Example:

i=10 J=15 if [ i –eq j ] then echo “ i is equal to j” else echo “ i is not equal to j” fi

Here we assign two integer variables i and j and the condition if both are equal or not using -eq.

2. String Comparison

string1 = string2	the strings are equal.
string1 != string2	the strings are not equal
−n string	string is not null
−z string	the string is null

Example:

var1=Linux var2=Linux if [ var1 = var2 ] then echo “ var1 and var2 strings are equal” else echo “ var1 and var2 strings are not equal” fi

Here we define two string variable and test the condition if they are equal or not.

3. File Comparison

-d	directory
-e	file exist
-f	Regular file
-g	SGID is set on file
-r	Readable file
-s	File is not zero in size
-u	SUID is set on file
-w	Writable file
-x	Executable file

Example:

if [ -f file.txt ] then echo “file.txt is a regular file” fi

 Here we test the type of file file.txt, is it regular file or directory or other.

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