实际上，@ Graeme的答案-和您的问题-只是引用了shell处理方式的副作用。"$@positional $*parameters".这些作用是在调用时由shell分配给其参数的，并且在以后的任何时间都使用内置set实用程序。可以随时调用它们，要么"$*"将每个位置拆分为第一个字符，"$IFS"要么用"$@"引号将每个位置拆分为所有"$IFS."
man set
NAME
set — set or unset options and positional parameters
SYNOPSIS
set [−abCefhmnuvx] [−o option] [argument...]
set [+abCefhmnuvx] [+o option] [argument...]
set −− [argument...]
set −o
set +o
如果已经有了要输入外壳程序的值，则不需要--三遍。Shell参数set能够-始终在任何时候而不只是在调用时（$ 0和-i除外）：
su - mikeserv -c 'set -- "$*" ; echo "$*" ;
set -- 4 5 6 ; echo "$*"' -- -- 7 8 9
7 8 9
4 5 6
而且所有这些shell引用都可能令人困惑。这样可以简化一些事情：
( set -- 4 5 6
su - mikeserv 4<<-\CMD /dev/fd/4 "$@"
echo $0 "$*"
set -- "$*"
echo "$*"
set -- 7 8 9
echo "$*"
CMD
)
/dev/fd/4 4 5 6
4 5 6
7 8 9
父shell的参数是set4、5和6，然后传递给su通过位置调用的子shellparameter "$@array".
请注意我( subshell )上面的命令是如何执行的-之所以这样做是因为我不想弄乱我当前的shell环境-因为我会无意中更改一些我宁愿做的事情set.
关于重定向：
首先，您的Unix系统可以处理文件-文件权限，文件内容，文件属性。可以以一种或另一种方式，将您使用的每个数据对象（至少应该以我的观点）作为文件进行寻址。重定向指向一个文件-仅此而已。A <<HERE-DOCUMENT将内联描述一个文件，然后将其重定向。解释外壳扩展或不解释外壳扩展。
询问者在下面的注释中指出，当他尝试以root用户身份使用此方法时，将收到权限错误。当我回答我建议他chown还是chgrp在/dev/fd/${num}特殊的文件，但是这可能不是最好的方法。他遇到此问题的原因root是授予read权限，而不是 execute权限。您可以避免exec通话，轻松解决此问题。与其/dev/fd/${num}直接在命令行上调用文件，不如：
su -c '. /dev/fd/'${num} ${num}<<SCRIPT
使用两个heredocs可以帮助转义。在每种情况下都会发生以下情况：
没有设置 <<HEREDOC
sh 3<<\CMD /dev/fd/3
( echo 'without set "$@" or \$@ in here-doc' ; echo
set -- '1 "2" 3' 4 "5 6"
su - mikeserv 4<<-UNQUOTED 5<<-\PREQUOTED /dev/fd/4
echo UNQUOTED; echo $0 "$*"
printf "%s\\t\\t%s\\t\\t%s\\t\\t%s\\n" $(printf "'%s' " "$@") \\
$@ '$@' "$@" '"$@"' "'$@'" \$@ '\$@' "\$@" '"\$@"'
. /dev/fd/5
UNQUOTED
echo PREQUOTED ; echo $0 "$*"
printf "%s\t\t%s\t\t%s\t\t%s\n" $(printf "'%s' " "$@") \
$@ '$@' "$@" '"$@"' \$@ '\$@' "\$@" '"\$@"'
PREQUOTED
)
CMD
输出值
without set "$@" or \$@ in here-doc
UNQUOTED
/dev/fd/3 1 2 3 4 5 6
1 "2" 3 4 5 6 1
2 3 4 5
6 1 "2" 3 4 5 6 1 2 3 4 5 6 "1 "2" 3 4 5 6"
'1 2 3 4 5 6' $@ "$@"
PREQUOTED
/dev/fd/5
'' $@ "$@" $@
\$@ $@ "\$@"
设置"$@"在<<HEREDOC
sh 3<<\CMD /dev/fd/3
( echo 'set "$@" and \$@ in here-doc' ; echo
set -- '1 "2" 3' 4 "5 6"
su - mikeserv 4<<-UNQUOTED 5<<-\PREQUOTED /dev/fd/4
set -- "$@" "\$@"
echo UNQUOTED; echo $0 "$*"
printf "%s\\t\\t%s\\t\\t%s\\t\\t%s\\n" $(printf "'%s' " "$@") \\
$@ '$@' "$@" '"$@"' "'$@'" \$@ '\$@' "\$@" '"\$@"'
. /dev/fd/5
UNQUOTED
set -- "$@" "\$@"
echo PREQUOTED ; echo $0 "$*"
printf "%s\t\t%s\t\t%s\t\t%s\n" $(printf "'%s' " "$@") \
$@ '$@' "$@" '"$@"' \$@ '\$@' "\$@" '"\$@"'
PREQUOTED
)
CMD
输出值
set "$@" and \$@ in here-doc
UNQUOTED
/dev/fd/3 1 2 3 4 5 6
1 "2" 3 4 5 6 1
2 3 4 5
6 1 "2" 3 4 5 6 1 2 3 4 5 6 "1 "2" 3 4 5 6"
'1 2 3 4 5 6' 1 2 3 4 5 6 $@ 1 2 3 4 5 6
"$@"
PREQUOTED
/dev/fd/5 1 2 3 4 5 6 $@
'1 2 3 4
5 6' '$@' 1 2 3 4 5 6
$@ $@ 1 2 3 4 5 6 $@
"$@" $@ \$@ $@
"\$@"
设置"$@"和更多<<HEREDOC
sh 3<<\CMD /dev/fd/3
( echo 'set "$@" and \$@ AND additional parameters in here-doc' ; echo
set -- '1 "2" 3' 4 "5 6"
su - mikeserv 4<<-UNQUOTED 5<<-\PREQUOTED /dev/fd/4
set -- "$@" "\$@" '7 "8" 9' 10 "11 12"
echo UNQUOTED; echo $0 "$*"
printf "%s\\t\\t%s\\t\\t%s\\t\\t%s\\n" $(printf "'%s' " "$@") \\
$@ '$@' "$@" '"$@"' "'$@'" \$@ '\$@' "\$@" '"\$@"'
. /dev/fd/5
UNQUOTED
set -- "$@" "\$@" '13 "14" 15' 16 "17 18"
echo PREQUOTED ; echo $0 "$*"
printf "%s\t\t%s\t\t%s\t\t%s\n" $(printf "'%s' " "$@") \
$@ '$@' "$@" '"$@"' \$@ '\$@' "\$@" '"\$@"'
PREQUOTED
)
CMD
输出值
set "$@" and \$@ AND additional parameters in here-doc
UNQUOTED
/dev/fd/3 1 2 3 4 5 6
1 "2" 3 4 5 6 1
2 3 4 5
6 1 "2" 3 4 5 6 1 2 3 4 5 6 "1 "2" 3 4 5 6"
'1 2 3 4 5 6' 1 2 3 4 5 6 7 "8" 9 10
11 12 $@ 1 2 3 4 5 6 7 "8" 9
10 11 12 "$@"
PREQUOTED
/dev/fd/5 1 2 3 4 5 6 7 "8" 9 10 11 12 $@ 13 "14" 15 16 17 18
'1 2 3 4
5 6' '7 "8"
9' '10' '11 12'
'$@' '13 "14" 15'
'16' '17 18' 1 2 3 4 5 6
7 "8" 9 10 11 12 $@
13 "14" 15 16 17 18 $@
1 2 3 4 5 6 7 "8" 9 10 11 12
$@ 13 "14" 15 16 17 18
"$@" $@ \$@ $@
"\$@"
bash 4.2.45同时在源帐户和目标帐户上使用。