Shell·xargs命令用法

本文节选自《Netkiller Shell 手札》

3.12. standard input/output

3.12.1. xargs - build and execute command lines from standard input

xargs命令用法

3.12.1.1. 格式化

xargs用作替换工具，读取输入数据重新格式化后输出。

			定义一个测试文件，内有多行文本数据：

cat >> test.txt <<EOF

a b c d e f g
h i j k l m n
o p q
r s t
u v w x y z

EOF

# cat test.txt 

a b c d e f g
h i j k l m n
o p q
r s t
u v w x y z


多行输入一行输出：

# cat test.txt | xargs
a b c d e f g h i j k l m n o p q r s t u v w x y z

等效
# cat test.txt | tr "n" " "
a b c d e f g h i j k l m n o p q r s t u v w x y z

-n选项多行输出：

# cat test.txt | xargs -n3
a b c
d e f
g h i
j k l
m n o
p q r
s t u
v w x
y z
# cat test.txt | xargs -n4
a b c d
e f g h
i j k l
m n o p
q r s t
u v w x
y z
# cat test.txt | xargs -n5
a b c d e
f g h i j
k l m n o
p q r s t
u v w x y
z


-d选项可以自定义一个定界符：

# echo "name|age|sex|birthday" | xargs -d"|"
name age sex birthday

结合-n选项使用：

# echo "name=Neo|age=30|sex=T|birthday=1980" | xargs -d"|" -n1
name=Neo
age=30
sex=T
birthday=1980

3.12.1.2. standard input

			# xargs < test.txt 
a b c d e f g h i j k l m n o p q r s t u v w x y z		
		
# cat /etc/passwd | cut -d : -f1 > users
# xargs -n1 < users echo "Your name is"
Your name is root
Your name is bin
Your name is daemon
Your name is adm
Your name is lp
Your name is sync
Your name is shutdown
Your name is halt
Your name is mail
Your name is operator
Your name is games
Your name is ftp
Your name is nobody
Your name is dbus
Your name is polkitd
Your name is avahi
Your name is avahi-autoipd
Your name is postfix
Your name is sshd
Your name is neo
Your name is ntp
Your name is opendkim
Your name is netkiller
Your name is tcpdump

3.12.1.3. -I 替换操作

复制所有图片文件到 /data/images 目录下：

ls *.jpg | xargs -n1 -I cp {} /data/images

			读取stdin，将格式化后的参数传递给命令xargs的一个选项-I，使用-I指定一个替换字符串{}，这个字符串在xargs扩展时会被替换掉，当-I与xargs结合使用，每一个参数命令都会被执行一次：

# echo "name=Neo|age=30|sex=T|birthday=1980" | xargs -d"|" -n1 | xargs -I {} echo "select * from tab where {} "
select * from tab where name=Neo 
select * from tab where age=30 
select * from tab where sex=T 
select * from tab where birthday=1980 

# xargs -I user echo "Hello user" <users 
Hello root
Hello bin
Hello daemon
Hello adm
Hello lp
Hello sync
Hello shutdown
Hello halt
Hello mail
Hello operator
Hello games
Hello ftp
Hello nobody
Hello dbus
Hello polkitd
Hello avahi
Hello avahi-autoipd
Hello postfix
Hello sshd
Hello netkiller
Hello neo
Hello tss
Hello ntp
Hello opendkim
Hello noreply
Hello tcpdump