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

#!/bin/bash

# "$*"和"$@"的古怪行为,
#+ 依赖于它们是否被""引用.
# 单词拆分和换行的不一致处理.

set -- "First one" "second" "third:one" "" "Fifth: :one"
# 设置这个脚本参数,$1,$2,等等.
echo $#

#################################
echo
echo "eg: 1-1"
echo 'IFS unchanged, using "$*"'
c=0
for i in "$*" 						# 引用
do echo "$((c+=1)): [$i]"		# 这行在下边的每个例子中都一样.
# Echo 参数.
done
echo ---
#-------------------------------
echo "eg: 1-2"
echo 'IFS unchanged, using $*'
c=0
for i in $*							# 未引用
do echo "$((c+=1)): [$i]"
done
echo ---
#################################

#################################
echo
echo "eg: 2-1"
echo 'IFS unchanged, using "$@"'
c=0
for i in "$@"
do echo "$((c+=1)): [$i]"
done
echo ---
#-------------------------------
echo "eg: 2-2"
echo 'IFS unchanged, using $@'
c=0
for i in $@
do echo "$((c+=1)): [$i]"
done
echo ---
#################################

#################################
echo
echo "eg: 3-1"
IFS=:
echo 'IFS=":", using "$*"'
c=0
for i in "$*"
do echo "$((c+=1)): [$i]"
done
echo ---
#-------------------------------
echo "eg: 3-2"
echo 'IFS=":", using $*'
c=0
for i in $*
do echo "$((c+=1)): [$i]"
done
echo ---
#################################

#################################
echo
echo "eg: 4-1"
var=$*
echo 'IFS=":", using "$var" (var=$*)'
c=0
for i in "$var"
do echo "$((c+=1)): [$i]"
done
echo ---
#-------------------------------
echo "eg: 4-2"
echo 'IFS=":", using $var (var=$*)'
c=0
for i in $var
do echo "$((c+=1)): [$i]"
done
echo ---
#################################

#################################
echo
echo "eg: 5-1"
var="$*"
echo 'IFS=":", using "$var" (var="$*")'
c=0
for i in "$var"
do echo "$((c+=1)): [$i]"
done
echo ---
#-------------------------------
echo "eg: 5-2"
echo 'IFS=":", using $var (var="$*")'
c=0
for i in $var
do echo "$((c+=1)): [$i]"
done
echo ---
#################################

#################################
echo
echo "eg: 6-1"
echo 'IFS=":", using "$@"'
c=0
for i in "$@"
do echo "$((c+=1)): [$i]"
done
echo ---
#-------------------------------
echo "eg: 6-2"
echo 'IFS=":", using $@'
c=0
for i in $@
do echo "$((c+=1)): [$i]"
done
echo ---
#################################

#################################
echo
echo "eg: 7-1"
var=$@
echo 'IFS=":", using $var (var=$@)'
c=0
for i in $var
do echo "$((c+=1)): [$i]"
done
echo ---
#-------------------------------
echo "eg: 7-2"
echo 'IFS=":", using "$var" (var=$@)'
c=0
for i in "$var"
do echo "$((c+=1)): [$i]"
done
echo ---
#################################

#################################
echo
echo "eg: 8-1"
var=$@
var="$@"
echo 'IFS=":", using "$var" (var="$@")'
c=0
for i in "$var"
do echo "$((c+=1)): [$i]"
done
echo ---
#-------------------------------
echo "eg: 8-2"
echo 'IFS=":", using $var (var="$@")'
c=0
for i in $var
do echo "$((c+=1)): [$i]"
done
#################################

echo

# 用 ksh 或者 zsh -y 来试试这个脚本.

exit 0

# This example script by Stephane Chazelas,
# and slightly modified by the document author.
################################End

运行结果：

5

eg: 1-1
IFS unchanged, using "$*"
1: [First one second third:one  Fifth: :one]
---
eg: 1-2
IFS unchanged, using $*
1: [First]
2: [one]
3: [second]
4: [third:one]
5: [Fifth:]
6: [:one]
---

eg: 2-1
IFS unchanged, using "$@"
1: [First one]
2: [second]
3: [third:one]
4: []
5: [Fifth: :one]
---
eg: 2-2
IFS unchanged, using $@
1: [First]
2: [one]
3: [second]
4: [third:one]
5: [Fifth:]
6: [:one]
---

eg: 3-1
IFS=":", using "$*"
1: [First one:second:third:one::Fifth: :one]
---
eg: 3-2
IFS=":", using $*
1: [First one]
2: [second]
3: [third]
4: [one]
5: []
6: [Fifth]
7: [ ]
8: [one]
---

eg: 4-1
IFS=":", using "$var" (var=$*)
1: [First one:second:third:one::Fifth: :one]
---
eg: 4-2
IFS=":", using $var (var=$*)
1: [First one]
2: [second]
3: [third]
4: [one]
5: []
6: [Fifth]
7: [ ]
8: [one]
---

eg: 5-1
IFS=":", using "$var" (var="$*")
1: [First one:second:third:one::Fifth: :one]
---
eg: 5-2
IFS=":", using $var (var="$*")
1: [First one]
2: [second]
3: [third]
4: [one]
5: []
6: [Fifth]
7: [ ]
8: [one]
---

eg: 6-1
IFS=":", using "$@"
1: [First one]
2: [second]
3: [third:one]
4: []
5: [Fifth: :one]
---
eg: 6-2
IFS=":", using $@
1: [First one]
2: [second]
3: [third]
4: [one]
5: []
6: [Fifth]
7: [ ]
8: [one]
---

eg: 7-1
IFS=":", using $var (var=$@)
1: [First one second third one  Fifth   one]
---
eg: 7-2
IFS=":", using "$var" (var=$@)
1: [First one second third one  Fifth   one]
---

eg: 8-1
IFS=":", using "$var" (var="$@")
1: [First one second third:one  Fifth: :one]
---
eg: 8-2
IFS=":", using $var (var="$@")
1: [First one second third]
2: [one  Fifth]
3: [ ]
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？