Shell Programming Basics

Receiving user parameters

#./example.sh One and three
The Shell scripting language includes variables for receiving user parameters, and based on the above command, the commonly used variables are as follows:

• Use $ A To get the file name of the shell script, the above example.sh
• Use $, $, $ ... corresponding to the N-position parameters, such as the One
• With $ #对应着该脚本执行时带有的参数个数, the above $ #等于3
• The $* corresponds to the parameters of all positions, the above $ #为one and the three
• With $? Represents the execution return value of the last command, 0 indicates success, and a value other than 0 indicates a failure
  <br/> Determine the user's parameters
  1. File Test statement
  2. Logical Test Statement
  3. Integer value comparison statement
  4. string comparison statements

Note: Therefore, the syntax format of the test statement is: [conditional expression], the conditional expression has a space before and after each, and there must be a space between the operand and the operator in the conditional expression!!!
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Common parameters for file testing

operator	function
-D	Test whether the file is a directory type
-E	Test whether the file exists
-F	Determine if it is a generic file
-R	Tests whether the current user has permission to read
-W	Tests whether the current user has permission to write
-X	Tests whether the current user has permission to execute

eg. #[-d/etc/fstab]
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Logical Test Operators

operator	function
&&	With operator, true on the left to calculate right
| |	Or operator, false on the left to calculate the right
!	Non-operator, true and false inverse

eg. #[-e/dev/cdrom] && echo "Exist"
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Integer comparison Operators

operator	function
-eq	is equal to
-ne	is not equal to
-gt	is greater than
-lt	is less than
-le	is less than or equal to
-ge	is greater than or equal to

eg. #[10-ge 10]
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string comparison operators

operator	function
=	Compare strings for the same content
！ =	Compare strings for different content
-Z	Determines whether the string contents are empty or undefined

eg. #[-Z $String]
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Process Control Statements

1. If statement
2. For statement
3. While statement
4. Case statement
   <BR/> If statement syntax

   Single Branch

   if 条件测试操作; then命令序列fi

   Dual Branch

   if 条件测试操作; then命令序列else命令序列fi

   Multi-Branch

   if 条件测试操作; then命令序列elif 条件测试操作; then命令序列else命令序列fi

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   For statement syntax

   for 变量名 in 取值列表do命令序列done

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   While statement syntax

   while 条件测试操作do命令序列done

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   Case statement syntax

   case 变量值 in模式1)命令序列;;模式2)命令序列;;......*)默认命令序列esac

Shell Programming Basics