Shell教程（三）：數組/Arrays、基本運算子_Shell

定義數組值：

一個陣列變數和標量變數之間的差異可以解釋如下。

說，你正試圖表示各種學生為變數集的名字。每一個單個變數是一個標量變數，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儲存所有上述提及的名稱。以下是最簡單的方法建立一個陣列變數分配一個值，其索引之一。這是表示，如下所示：

array_name[index]=value

array_name 是數組名，索引是在陣列中，你要設定的項目索引，值是你想要的值設定該項目。 

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在這裡初始化數組的文法：

set -A array_name value1 value2 ... valuen

如果您使用的是bash shell中，這裡是初始化數組的文法：

array_name=(value1 ... valuen)

訪問數組值：

當您設定任何陣列變數，並可訪問它，如下所示：

${array_name[index]}

在這裡，array_name是數組的名稱，index是索引進行訪問的值。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

您可以訪問數組中的所有項目通過以下方式之一：

${array_name[*]}

${array_name[@]}

 array_name 是數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[@]}"

這將產生以下結果：

$./test.sh

First Method: Zara Qadir Mahnaz Ayan Daisy

Second Method: Zara Qadir Mahnaz Ayan Daisy

 

 

有各種不同的運算子shell都支援。本教程是基於預設shell（Bourne），所以我們要涵蓋所有重要的Bourne Shell運算子。

有以下的運算子，我們將要討論的：

·        算術運算子。

·        關係運算子。

·        布林運算子。

·        字串運算子。

·        檔案測試操作。

Bourne shell的最初並沒有任何機制來執行簡單的算術，但它使用外部程式，無論是awk或必須簡單的程式expr。

下面是簡單的例子，把兩個數相加：

#!/bin/sh

val=`expr 2 + 2`

echo "Total value : $val"

這將產生以下結果：

Total value : 4

記下有以下幾點：

·        運算子和運算式之間必須有空格，例如2+2是不正確的，因為它應該寫成2 + 2。

·        ``，稱為倒逗號之間應包含完整的表達。 算術運算子：

算術運算子有以下Bourne Shell支援。

假設變數a=10,變數b=20：

算術運算子例子

運算子

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，這裡要注意，所有的條件式將放在方括弧內，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。

所有的算術計算，使用長整數。 關係運算子：

Bourne Shell的支援，關係運算子的具體數值。這些運算子不能使用字串值，除非它們的值是數字。

例如，運算子將努力檢查10和20之間的關係，以及在“10”和“20”，但不是“10”和“21”之間。

假設變數a=10,變數b=20：

關係運算子

運算子

描述

樣本

-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.

這裡要注意，所有的條件式將放在方括弧內，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。 布爾運算：

布林運算子有以下Bourne Shell的支援。

假設變數一個變數b=10，然後變數b=20：

布爾運算樣本

運算子

描述

樣本

!

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. 字串運算子：

有下列字串運算由Bourne Shell支援。

假設變數a=“abc”和變數b=“efg”：

關係運算例子

運算子

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. 檔案測試操作：

有以下是操作測試Unix檔案相關聯的各種屬性。

假設一個的變數檔案儲存現有檔案名稱“test”，其大小為100位元組，有讀，寫和執行許可權：

檔案測試操作例子

操作符

描述

樣本

-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:

以下連結將在C Shell運算子給出簡單的用法。

C Shell 運算子 Korn Shell 運算子:

以下連結將在Korn  Shell運算子給出簡單的用法

Korn Shell 運算子

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