Bash Script Programming five-condition statements

Use the preceding example to write a conditional expression. If the first parameter does not exist, no parameter is output; otherwise, the first parameter is output.

#!/bin/bashif [ -n "$1" ]then    echo "1st parameter: $1"else    echo "no parameter"fi

Enter the command with parameters:

$ ./test.sh 'this is a test'1st parameter: this is a test

Enter the command without parameters:

$ ./test.shno parameter

Explain the Condition Statement first:

If [...]

Then

...

Else

...

Fi

... Indicates where statements can be written.

You must end the entire Condition Statement with Fi.

Note that [...] square brackets must be separated by spaces.

-N is an operator that determines whether the subsequent parameter length is 0. If it is not 0, true is returned. If it is 0, false is returned.

This document is a good introduction. For details, refer:

Http://v.youku.com/v_show/id_XNDQ5ODE3MDQw.html

The complex conditional expressions are as follows:

if condition1thenstatement1statement2..........elif condition2thenstatement3statement4........    elif condition3thenstatement5statement6........    fi

In addition to-N, there are other operators available for use:

Operator	Produces true if...	Number of operands
-N	Operand non zero length	1
-Z	Operand has zero length	1
-D	There exists a directory whose name isOperand	1
-F	There exists a file whose name isOperand	1
-EQ	The operands are integers and they are equal	2
-NEQ	The opposite of-EQ	2
=	The operands are equal (as strings)	2
! =	Opposite of =	2
-Lt	Operand1Is strictly lessOperand2(Both operands shoshould be integers)	2
-GT	Operand1Is strictly greaterOperand2(Both operands shoshould be integers)	2
-Ge	Operand1Is greater than or equalOperand2(Both operands shoshould be integers)	2
-Le	Operand1Is less than or equalOperand2(Both operands shoshould be integers)	2

The double operand operator is used as follows:

$r -eq 1