bash编程之$#, $*, $@变量

           阅读了高级bash脚本编程一书，贴上有关$#, $*, $@的相关内容已经脚本实例。

位置参数：

$1, $2.. :
      位置参数从参数 0 开始。参数 0 引用启动 bash 的程序的名称，如果函数在 shell 脚本中运行，则引用
shell 脚本的名称。有关该参数的其他信息，比如 bash 由 -c 参数启动，请参阅 bash 手册页面。由单引号或
双引号包围的字符串被作为一个参数进行传递，传递时会去掉引号。 如果是双引号，则在调用函数之前将对
 $HOME 之类的 shell 变量进行扩展。对于包含嵌入空白或其他字符（这些空白或字符可能对 shell 有特殊意
义）的参数，需要使用单引号或双引号进行传递。
$* :
      位置参数从参数 1 开始。如果在双引号中进行扩展，则扩展就是一个词，由 IFS 特殊变量的第一个字符
将参数分开，如果 IFS 为空，则没有间隔空格。IFS 的默认值是空白、制表符和换行符。如果没有设置 IFS，
则使用空白作为分隔符（仅对默认 IFS 而言）。
$@ :
      位置参数从参数 1 开始。如果在双引号中进行扩展，则每个参数都会成为一个词，因此 “$@” 与
“$1” “$2” 等效。如果参数有可能包含嵌入空白，那么您将需要使用这种形式。
$# :
      参数数量（不包含参数 0）。

脚本实例：
      程序实例是最能说明问题的了

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1. #!/bin/bash
2. 
   
3. # "$*"和"$@"的古怪行为,
4. #+ 依赖于它们是否被""引用.
5. # 单词拆分和换行的不一致处理.
6. 
   
7. set -- "First one" "second" "third:one" "" "Fifth: :one"
8. # 设置这个脚本参数,$1,$2,等等.
9. echo $#
10. 
    
11. #################################
12. echo
13. echo "eg: 1-1"
14. echo 'IFS unchanged, using "$*"'
15. c=0
16. for i in "$*" # 引用
17. do echo "$((c+=1)): [$i]" # 这行在下边的每个例子中都一样.
18. # Echo 参数.
19. done
20. echo ---
21. #-------------------------------
22. echo "eg: 1-2"
23. echo 'IFS unchanged, using $*'
24. c=0
25. for i in $* # 未引用
26. do echo "$((c+=1)): [$i]"
27. done
28. echo ---
29. #################################
30. 
    
31. #################################
32. echo
33. echo "eg: 2-1"
34. echo 'IFS unchanged, using "$@"'
35. c=0
36. for i in "$@"
37. do echo "$((c+=1)): [$i]"
38. done
39. echo ---
40. #-------------------------------
41. echo "eg: 2-2"
42. echo 'IFS unchanged, using $@'
43. c=0
44. for i in $@
45. do echo "$((c+=1)): [$i]"
46. done
47. echo ---
48. #################################
49. 
    
50. #################################
51. echo
52. echo "eg: 3-1"
53. IFS=:
54. echo 'IFS=":", using "$*"'
55. c=0
56. for i in "$*"
57. do echo "$((c+=1)): [$i]"
58. done
59. echo ---
60. #-------------------------------
61. echo "eg: 3-2"
62. echo 'IFS=":", using $*'
63. c=0
64. for i in $*
65. do echo "$((c+=1)): [$i]"
66. done
67. echo ---
68. #################################
69. 
    
70. #################################
71. echo
72. echo "eg: 4-1"
73. var=$*
74. echo 'IFS=":", using "$var" (var=$*)'
75. c=0
76. for i in "$var"
77. do echo "$((c+=1)): [$i]"
78. done
79. echo ---
80. #-------------------------------
81. echo "eg: 4-2"
82. echo 'IFS=":", using $var (var=$*)'
83. c=0
84. for i in $var
85. do echo "$((c+=1)): [$i]"
86. done
87. echo ---
88. #################################
89. 
    
90. #################################
91. echo
92. echo "eg: 5-1"
93. var="$*"
94. echo 'IFS=":", using "$var" (var="$*")'
95. c=0
96. for i in "$var"
97. do echo "$((c+=1)): [$i]"
98. done
99. echo ---
100. #-------------------------------
101. echo "eg: 5-2"
102. echo 'IFS=":", using $var (var="$*")'
103. c=0
104. for i in $var
105. do echo "$((c+=1)): [$i]"
106. done
107. echo ---
108. #################################
109. 
     
110. #################################
111. echo
112. echo "eg: 6-1"
113. echo 'IFS=":", using "$@"'
114. c=0
115. for i in "$@"
116. do echo "$((c+=1)): [$i]"
117. done
118. echo ---
119. #-------------------------------
120. echo "eg: 6-2"
121. echo 'IFS=":", using $@'
122. c=0
123. for i in $@
124. do echo "$((c+=1)): [$i]"
125. done
126. echo ---
127. #################################
128. 
     
129. #################################
130. echo
131. echo "eg: 7-1"
132. var=$@
133. echo 'IFS=":", using $var (var=$@)'
134. c=0
135. for i in $var
136. do echo "$((c+=1)): [$i]"
137. done
138. echo ---
139. #-------------------------------
140. echo "eg: 7-2"
141. echo 'IFS=":", using "$var" (var=$@)'
142. c=0
143. for i in "$var"
144. do echo "$((c+=1)): [$i]"
145. done
146. echo ---
147. #################################
148. 
     
149. #################################
150. echo
151. echo "eg: 8-1"
152. var=$@
153. var="$@"
154. echo 'IFS=":", using "$var" (var="$@")'
155. c=0
156. for i in "$var"
157. do echo "$((c+=1)): [$i]"
158. done
159. echo ---
160. #-------------------------------
161. echo "eg: 8-2"
162. echo 'IFS=":", using $var (var="$@")'
163. c=0
164. for i in $var
165. do echo "$((c+=1)): [$i]"
166. done
167. #################################
168. 
     
169. echo
170. 
     
171. # 用 ksh 或者 zsh -y 来试试这个脚本.
172. 
     
173. exit 0
174. 
     
175. # This example script by Stephane Chazelas,
176. # and slightly modified by the document author.
177. ################################End

运行结果：

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1. 5
2. 
   
3. eg: 1-1
4. IFS unchanged, using "$*"
5. 1: [First one second third:one Fifth: :one]
6. ---
7. eg: 1-2
8. IFS unchanged, using $*
9. 1: [First]
10. 2: [one]
11. 3: [second]
12. 4: [third:one]
13. 5: [Fifth:]
14. 6: [:one]
15. ---
16. 
    
17. eg: 2-1
18. IFS unchanged, using "$@"
19. 1: [First one]
20. 2: [second]
21. 3: [third:one]
22. 4: []
23. 5: [Fifth: :one]
24. ---
25. eg: 2-2
26. IFS unchanged, using $@
27. 1: [First]
28. 2: [one]
29. 3: [second]
30. 4: [third:one]
31. 5: [Fifth:]
32. 6: [:one]
33. ---
34. 
    
35. eg: 3-1
36. IFS=":", using "$*"
37. 1: [First one:second:third:one::Fifth: :one]
38. ---
39. eg: 3-2
40. IFS=":", using $*
41. 1: [First one]
42. 2: [second]
43. 3: [third]
44. 4: [one]
45. 5: []
46. 6: [Fifth]
47. 7: [ ]
48. 8: [one]
49. ---
50. 
    
51. eg: 4-1
52. IFS=":", using "$var" (var=$*)
53. 1: [First one:second:third:one::Fifth: :one]
54. ---
55. eg: 4-2
56. IFS=":", using $var (var=$*)
57. 1: [First one]
58. 2: [second]
59. 3: [third]
60. 4: [one]
61. 5: []
62. 6: [Fifth]
63. 7: [ ]
64. 8: [one]
65. ---
66. 
    
67. eg: 5-1
68. IFS=":", using "$var" (var="$*")
69. 1: [First one:second:third:one::Fifth: :one]
70. ---
71. eg: 5-2
72. IFS=":", using $var (var="$*")
73. 1: [First one]
74. 2: [second]
75. 3: [third]
76. 4: [one]
77. 5: []
78. 6: [Fifth]
79. 7: [ ]
80. 8: [one]
81. ---
82. 
    
83. eg: 6-1
84. IFS=":", using "$@"
85. 1: [First one]
86. 2: [second]
87. 3: [third:one]
88. 4: []
89. 5: [Fifth: :one]
90. ---
91. eg: 6-2
92. IFS=":", using $@
93. 1: [First one]
94. 2: [second]
95. 3: [third]
96. 4: [one]
97. 5: []
98. 6: [Fifth]
99. 7: [ ]
100. 8: [one]
101. ---
102. 
     
103. eg: 7-1
104. IFS=":", using $var (var=$@)
105. 1: [First one second third one Fifth one]
106. ---
107. eg: 7-2
108. IFS=":", using "$var" (var=$@)
109. 1: [First one second third one Fifth one]
110. ---
111. 
     
112. eg: 8-1
113. IFS=":", using "$var" (var="$@")
114. 1: [First one second third:one Fifth: :one]
115. ---
116. eg: 8-2
117. IFS=":", using $var (var="$@")
118. 1: [First one second third]
119. 2: [one Fifth]
120. 3: [ ]
121. 4: [one]

对于之前的1-6的实例，没有问题
但是对于实例7，为何作为$@直接传递给var后，var的值中却没有IFS的分割符显示，比如实例5-1？