GNU parallel可以并行地执行shell命令。看一个简单的例子:

# ls
a  b  c
# cat a
aaaa

# cat b
bbbb

# cat c
cccc

# parallel cat ::: *
aaaa

bbbb

cccc

上面的例子输出了abc3个文件的内容。:::告诉GNU parallel从命令行而不是stdin读取参数,而shell会把*扩展成当前目录下的文件名。

再看一个例子:

# parallel sleep {}\; echo {} ::: 2 1 4 3
1
2
3
4
# parallel -k sleep {}\; echo {} ::: 2 1 4 3
2
1
4
3

正常情况下,完成一个jobparallel就会把这个job的内容输出。-k选项保证输出顺序和输入顺序一致。而{}会替换成input line

GNU parallel不会把多个输出的内容混杂在一起,对比下列两个命令输出:

# traceroute foss.org.my & traceroute debian.org & traceroute freenetproject.org & wait
[1] 4920
[2] 4921
[3] 4922
traceroute to debian.org (149.20.20.20), 30 hops max, 60 byte packets
traceroute to freenetproject.org (80.68.94.117), 30 hops max, 60 byte packets
foss.org.my: Name or service not known
Cannot handle "host" cmdline arg `foss.org.my' on position 1 (argc 1)
[1]   Exit 2                  traceroute foss.org.my
 1  16.187.248.2 (16.187.248.2)  1.705 ms  1.709 ms  2.067 ms
 1  16.187.248.2 (16.187.248.2)  1.315 ms  1.314 ms  1.618 ms
......

# parallel traceroute ::: foss.org.my debian.org freenetproject.org
foss.org.my: Name or service not known
Cannot handle "host" cmdline arg `foss.org.my' on position 1 (argc 1)
traceroute to debian.org (140.211.15.34), 30 hops max, 60 byte packets
 1  16.187.248.2 (16.187.248.2)  1.871 ms  1.857 ms  2.151 ms
......
traceroute to freenetproject.org (80.68.94.117), 30 hops max, 60 byte packets
 1  16.187.248.2 (16.187.248.2)  2.175 ms  2.471 ms  2.471 ms
 2  16.160.221.81 (16.160.221.81)  0.456 ms  0.463 ms  0.463 ms
......

参考资料:
GNU Parallel: The Command-Line Power Tool
GNU Parallel manual