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Shell教程（三）：数组/Arrays、基本运算符

發(fā)布時間：2025/3/21 编程问答 19 豆豆

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定義數(shù)組值：

一個數(shù)組變量和標(biāo)量變量之間的差異可以解釋如下。

說，你正試圖表示各種學(xué)生為變量集的名字。每一個單個變量是一個標(biāo)量變量，如下所示：

NAME01="Zara" NAME02="Qadir" NAME03="Mahnaz" NAME04="Ayan" NAME05="Daisy"

我們可以用一個單一的陣列來存儲所有上述提及的名稱。以下是最簡單的方法創(chuàng)建一個數(shù)組變量分配一個值，其索引之一。這是表示，如下所示：

array_name[index]=value

array_name?是數(shù)組名，索引是在陣列中，你要設(shè)置的項(xiàng)目索引，值是你想要的值設(shè)置該項(xiàng)目。?

作為一個例子，下面的命令：

NAME[0]="Zara" NAME[1]="Qadir" NAME[2]="Mahnaz www.yiibai.com" NAME[3]="Ayan" NAME[4]="Daisy"

如果您使用的是ksh shell在這里初始化數(shù)組的語法：

set -A array_name value1 value2 ... valuen

如果您使用的是bash shell中，這里是初始化數(shù)組的語法：

array_name=(value1 ... valuen)

訪問數(shù)組值：

當(dāng)您設(shè)置任何數(shù)組變量，并可訪問它，如下所示：

${array_name[index]}

在這里，array_name是數(shù)組的名稱，index是索引進(jìn)行訪問的值。下面是一個簡單的例子：

#!/bin/sh ? NAME[0]="Zara" NAME[1]="Qadir" NAME[2]="Mahnaz" NAME[3]="Ayan" NAME[4]="Daisy" echo "First Index: ${NAME[0]}" echo "Second Index: ${NAME[1]}"

This would producefollowing result:

$./test.sh First Index: Zara Second Index: Qadir

您可以訪問數(shù)組中的所有項(xiàng)目通過以下方式之一：

${array_name[*]} ${array_name[@]}

?array_name 是數(shù)組的名字你所感興趣的以下是個最簡單的例子：

#!/bin/sh ? NAME[0]="Zara" NAME[1]="Qadir" NAME[2]="Mahnaz" NAME[3]="Ayan" NAME[4]="Daisy" echo "First Method: ${NAME[*]}" echo "Second Method: ${NAME[@]}"

這將產(chǎn)生以下結(jié)果：

$./test.sh First Method: Zara Qadir Mahnaz Ayan Daisy Second Method: Zara Qadir Mahnaz Ayan Daisy

有各種不同的運(yùn)算符shell都支持。本教程是基于默認(rèn)shell（Bourne），所以我們要涵蓋所有重要的Bourne Shell運(yùn)算符。

有以下的運(yùn)算符，我們將要討論的：

·????????算術(shù)運(yùn)算符。

·????????關(guān)系運(yùn)算符。

·????????布爾運(yùn)算符。

·????????字符串運(yùn)算符。

·????????文件測試操作。

Bourne shell的最初并沒有任何機(jī)制來執(zhí)行簡單的算術(shù)，但它使用外部程序，無論是awk或必須簡單的程序expr。

下面是簡單的例子，把兩個數(shù)相加：

#!/bin/sh ? val=`expr 2 + 2` echo "Total value : $val"

這將產(chǎn)生以下結(jié)果：

Total value : 4

記下有以下幾點(diǎn)：

·????????運(yùn)算符和表達(dá)式之間必須有空格，例如2+2是不正確的，因?yàn)樗鼞?yīng)該寫成2 + 2。

·????????``，稱為倒逗號之間應(yīng)包含完整的表達(dá)。

算術(shù)運(yùn)算符：

算術(shù)運(yùn)算符有以下Bourne Shell支持。

假設(shè)變量a=10,變量b=20：

算術(shù)運(yùn)算符例子

運(yùn)算符	描述	例子
+	Addition - Adds values on either side of the operator	`expr $a + $b` will give 30
-	Subtraction - Subtracts right hand operand from left hand operand	`expr $a - $b` will give -10
*	Multiplication - Multiplies values on either side of the operator	`expr $a * $b` will give 200
/	Division - Divides left hand operand by right hand operand	`expr $b / $a` will give 2
%	Modulus - Divides left hand operand by right hand operand and returns remainder	`expr $b % $a` will give 0
=	Assignment - Assign right operand in left operand	a=$b would assign value of b into a
==	Equality - Compares two numbers, if both are same then returns true.	[ $a == $b ] would return false.
!=	Not Equality - Compares two numbers, if both are different then returns true.	[ $a != $b ] would return true.

這是非常重要的，這里要注意，所有的條件式將放在方括號內(nèi)，他們身邊有一個空格，例如 [ $a == $b ]是正確的，為[$a==$b]?是不正確的。

所有的算術(shù)計(jì)算，使用長整數(shù)。

關(guān)系運(yùn)算符：

Bourne Shell的支持，關(guān)系運(yùn)算符的具體數(shù)值。這些運(yùn)算符不能使用字符串值，除非它們的值是數(shù)字。

例如，運(yùn)算符將努力檢查10和20之間的關(guān)系，以及在“10”和“20”，但不是“10”和“21”之間。

假設(shè)變量a=10,變量b=20：

關(guān)系運(yùn)算符

運(yùn)算符	描述	示例
-eq	Checks if the value of two operands are equal or not, if yes then condition becomes true.	[ $a -eq $b ] is not true.
-ne	Checks if the value of two operands are equal or not, if values are not equal then condition becomes true.	[ $a -ne $b ] is true.
-gt	Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.	[ $a -gt $b ] is not true.
-lt	Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.	[ $a -lt $b ] is true.
-ge	Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.	[ $a -ge $b ] is not true.
-le	Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.	[ $a -le $b ] is true.

這里要注意，所有的條件式將放在方括號內(nèi)，他們周圍有一個空格，這是非常重要的，例如?[ $a <= $b]是正確的，?[$a <= $b]是不正確的。

布爾運(yùn)算：

布爾運(yùn)算符有以下Bourne Shell的支持。

假設(shè)變量一個變量b=10，然后變量b=20：

布爾運(yùn)算示例

運(yùn)算符	描述	示例
!	This is logical negation. This inverts a true condition into false and vice versa.	[ ! false ] is true.
-o	This is logical OR. If one of the operands is true then condition would be true.	[ $a -lt 20 -o $b -gt 100 ] is true.
-a	This is logical AND. If both the operands are true then condition would be true otherwise it would be false.	[ $a -lt 20 -a $b -gt 100 ] is false.

字符串運(yùn)算符：

有下列字符串運(yùn)算由Bourne Shell支持。

假設(shè)變量a=“abc”和變量b=“efg”：

關(guān)系運(yùn)算例子

運(yùn)算符	描述	例子
=	Checks if the value of two operands are equal or not, if yes then condition becomes true.	[ $a = $b ] is not true.
!=	Checks if the value of two operands are equal or not, if values are not equal then condition becomes true.	[ $a != $b ] is true.
-z	Checks if the given string operand size is zero. If it is zero length then it returns true.	[ -z $a ] is not true.
-n	Checks if the given string operand size is non-zero. If it is non-zero length then it returns true.	[ -z $a ] is not false.
str	Check if str is not the empty string. If it is empty then it returns false.	[ $a ] is not false.

文件測試操作：

有以下是操作測試Unix文件相關(guān)聯(lián)的各種屬性。

假設(shè)一個的變量文件保存現(xiàn)有文件名“test”，其大小為100字節(jié)，有讀，寫和執(zhí)行權(quán)限：

文件測試操作例子

操作符	描述	示例
-b file	Checks if file is a block special file if yes then condition becomes true.	[ -b $file ] is false.
-c file	Checks if file is a character special file if yes then condition becomes true.	[ -b $file ] is false.
-d file	Check if file is a directory if yes then condition becomes true.	[ -d $file ] is not true.
-f file	Check if file is an ordinary file as opposed to a directory or special file if yes then condition becomes true.	[ -f $file ] is true.
-g file	Checks if file has its set group ID (SGID) bit set if yes then condition becomes true.	[ -g $file ] is false.
-k file	Checks if file has its sticky bit set if yes then condition becomes true.	[ -k $file ] is false.
-p file	Checks if file is a named pipe if yes then condition becomes true.	[ -p $file ] is false.
-t file	Checks if file descriptor is open and associated with a terminal if yes then condition becomes true.	[ -t $file ] is false.
-u file	Checks if file has its set user id (SUID) bit set if yes then condition becomes true.	[ -u $file ] is false.
-r file	Checks if file is readable if yes then condition becomes true.	[ -r $file ] is true.
-w file	Check if file is writable if yes then condition becomes true.	[ -w $file ] is true.
-x file	Check if file is execute if yes then condition becomes true.	[ -x $file ] is true.
-s file	Check if file has size greater than 0 if yes then condition becomes true.	[ -s $file ] is true.
-e file	Check if file exists. Is true even if file is a directory but exists.	[ -e $file ] is true.

C Shell 操作符:

以下鏈接將在C Shell運(yùn)算符給出簡單的用法。

C Shell 運(yùn)算符

Korn Shell 運(yùn)算符:

以下鏈接將在Korn??Shell運(yùn)算符給出簡單的用法

Korn Shell 運(yùn)算符

from: http://www.yiibai.com/shell/what_is_shell.html#

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