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146 lines
3.5 KiB
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146 lines
3.5 KiB
Markdown
Shell Scripting – Checking Conditions with if
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================================================================================
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In Bourne Shell if statement checks whether a condition is true or not. If so , the shell executes the block of code associated with the if statement. If the statement is not true , the shell jumps beyond the end of the if statement block & Continues on.
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### Syntax of if Statement : ###
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if [ condition_command ]
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then
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command1
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command2
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……..
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last_command
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fi
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#### Example: ####
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#!/bin/bash
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number=150
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if [ $number -eq 150 ]
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then
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echo "Number is 150"
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fi
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#### if-else Statement : ####
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In addition to the normal if statement , we can extend the if statement with an else block. The basic idea is that if the statement is true , then execute the if block. If the statement is false , then execute the else block.
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#### Syntax : ####
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if [ condition_command ]
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then
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command1
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command2
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……..
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last_command
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else
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command1
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command2
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……..
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last_command
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fi
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#### Example: ####
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#!/bin/bash
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number=150
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if [ $number -gt 250 ]
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then
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echo "Number is greater"
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else
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echo "Number is smaller"
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fi
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### If..elif..else..fi Statement (Short for else if) ###
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The Bourne shell syntax for the if statement allows an else block that gets executed if the test is not true. We can nest if statement , allowing for multiple conditions. As an alternative, we can use the elif construct , shot for else if.
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#### Syntax : ####
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if [ condition_command ]
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then
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command1
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command2
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……..
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last_command
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elif [ condition_command2 ]
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then
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command1
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command2
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……..
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last_command
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else
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command1
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command2
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……..
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last_command
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fi
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#### Example : ####
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#!/bin/bash
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number=150
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if [ $number -gt 300 ]
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then
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echo "Number is greater"
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elif [ $number -lt 300 ]
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then
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echo "Number is Smaller"
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else
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echo "Number is equal to actual value"
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fi
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### Nested if statements : ###
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If statement and else statement can be nested in a bash script. The keyword ‘fi’ shows the end of the inner if statement and all if statement should end with the keyword ‘fi’.
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Basic **syntax of nested** if is shown below :
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if [ condition_command ]
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then
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command1
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command2
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……..
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last_command
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else
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if [ condition_command2 ]
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then
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command1
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command2
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……..
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last_command
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else
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command1
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command2
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……..
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last_command
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fi
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fi
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#### Example: ####
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#!/bin/bash
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number=150
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if [ $number -eq 150 ]
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then
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echo "Number is 150"
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else
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if [ $number -gt 150 ]
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then
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echo "Number is greater"
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else
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echo "'Number is smaller"
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fi
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fi
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--------------------------------------------------------------------------------
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via: http://www.linuxtechi.com/shell-scripting-checking-conditions-with-if/
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作者：[Pradeep Kumar][a]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](http://linux.cn/) 荣誉推出
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[a]:http://www.linuxtechi.com/author/pradeep/ |