把一個shell命令的輸出作為另一個shell命令的輸入；特殊變量$0, $#, $*, $@, $?, $$，以及"$*", "$@"代表的含義

本地有兩個文件： arg.txt 和 about.sh。

目標是把arg.txt里的內容輸出，並作為about.sh的輸入。

 

先看arg.txt里存的是什么：

[liusiyi@localhost ~]$ cat arg.txt
Bob
Ella
Justin
Christin
Steven
Olivia

 

再看 about.sh里存的是什么（其實是一段對Shell特殊變量的解釋，包括 $0, $#, $*, $@, $?, $$）：

  [liusiyi@localhost ~]$ cat about.sh

#!/bin/bash
echo "File name, \$0: $0"
echo "First argument, \$1: $1"
echo "Second argument, \$2: $2"
echo "Quated values, \$*: $*"
echo "Quated values, \$@: $@"
echo "Shell Id, \$$: $$"
echo "Return value (success 0, fail 1), \$?: $?"
echo "Total # of arguments, \$#: $#"
echo -e "\nSee differences about \$*, \$@, \"\$*\", and \"\$@\" as below:"
echo "---- print each argument from \$* ----"
count=0
for var in $*
do
count=$((count+1))
echo "$var"
done
echo "(totally $count)"

echo "---- print each argument from \$@ ----"
count=0
for var in $@
do
count=$((count+1))
echo "$var"
done
echo "(totally $count)"

echo "---- print each argument from \"\$*\" ----"
count=0
for var in "$*"
do
count=$((count+1))
echo "$var"
done
echo "(totally $count)"

echo "---- print each argument from \"\$@\" ----"
count=0
for var in "$@"
do
count=$((count+1))
echo "$var"
done
echo "(totally $count)"

echo "----------------end--------------"

 

步驟一，把arg.txt的內容傳給變量a：

[liusiyi@localhost ~]$ a=$(cat arg.txt)

 

步驟二，查看變量a的值：

[liusiyi@localhost ~]$ echo $a
Bob Ella Justin Christin Steven Olivia

 

步驟三，變量a的值被about.sh調用，顯示了$0, $#, $*, $@, $?, $$，以及"$*", "$@"在這個命令中的真實值：

[liusiyi@localhost ~]$ about.sh $a
File name, $0: ./about.sh
First argument, $1: Bob
Second argument, $2: Ella
Quated values, $*: Bob Ella Justin Christin Steven Olivia
Quated values, $@: Bob Ella Justin Christin Steven Olivia
Shell Id, $$: 25985
Return value (success 0, fail 1), $?: 0
Total # of arguments, $#: 6

See differences about $*, $@, "$*", and "$@" as below:
---- print each argument from $* ----
Bob
Ella
Justin
Christin
Steven
Olivia
(totally 6)
---- print each argument from $@ ----
Bob
Ella
Justin
Christin
Steven
Olivia
(totally 6)
---- print each argument from "$*" ----
Bob Ella Justin Christin Steven Olivia
(totally 1)
---- print each argument from "$@" ----
Bob
Ella
Justin
Christin
Steven
Olivia
(totally 6)
----------------end--------------

注意，被雙引號包含時，"$*" 的參數被當做一個整體，所以遍歷里面的元素之后 totally count=1；而 "$@" 依舊是遍歷每一個參數，所以count=6

 

以上步驟也可以簡寫為：

[liusiyi@localhost ~]$ about.sh $(cat arg.txt)