有各種不同的運算符shell都支持。本教學是基於默認shell（Bourne），所以我們要涵蓋所有重要的Bourne Shell運算符。

有以下的運算符，我們將要討論的：

• 算術運算符。

• 關係運算符。

• 布爾運算符。

• 字符串運算符。

• 文件測試操作。

Bourne shell的最初並冇有任何機製來執行簡單的算術，但它使用外部程序，無論是awk或必須簡單的程序expr。

下麵是簡單的例子，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：

• 運算符和表達式之間必須有空格，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。

算術運算符：

算術運算符有以下Bourne Shell支持。

假設變量a=10,變量b=20：

算術運算符例子

運算符	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，這裡要注意，所有的條件式將放在方括號內，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。

關係運算符：

Bourne Shell的支持，關係運算符的具體數值。這些運算符不能使用字符串值，除非它們的值是數字。

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

假設變量a=10,變量b=20：

關係運算符

運算符	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.

這裡要注意，所有的條件式將放在方括號內，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：

布爾運算符有以下Bourne Shell的支持。

假設變量一個變量b=10，然後變量b=20：

布爾運算示例

運算符	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.

字符串運算符：

有下列字符串運算由Bourne Shell支持。

假設變量a=“abc”和變量b=“efg”：

關係運算例子

運算符	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文件相關聯的各種屬性。

假設一個的變量文件保存現有文件名“test”，其大小為100字節，有讀，寫和執行權限：

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運算符給出簡單的用法。

C Shell 運算符

Korn Shell 運算符:

以下鏈接將在Korn  Shell運算符給出簡單的用法

Korn Shell 運算符