有没有更好的方法在 bash 中运行命令 N 次？
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Is there a better way to run a command N times in bash?
提问by bstpierre
I occasionally run a bash command line like this:
我偶尔会像这样运行 bash 命令行：
n=0; while [[ $n -lt 10 ]]; do some_command; n=$((n+1)); done
To run some_commanda number of times in a row -- 10 times in this case.
some_command连续运行多次——在本例中为 10 次。
Often some_commandis really a chain of commands or a pipeline.
通常some_command实际上是一个命令链或一个管道。
Is there a more concise way to do this?
有没有更简洁的方法来做到这一点？
回答by Joe Koberg
for run in {1..10}
do
command
done
Or as a one-liner for those that want to copy and paste easily:
或者作为那些想要轻松复制和粘贴的人的单行：
for run in {1..10}; do command; done
回答by BatchyX
Using a constant:
使用常量：
for ((n=0;n<10;n++)); do some_command; done
Using a variable (can include math expressions):
使用变量（可以包括数学表达式）：
x=10; for ((n=0; n < (x / 2); n++)); do some_command; done
回答by mitnk
Another simple way to hack it:
另一种简单的破解方法：
seq 20 | xargs -Iz echo "Hi there"
run echo 20 times.
运行 echo 20 次。
Notice that seq 20 | xargs -Iz echo "Hi there z"would output:
请注意，seq 20 | xargs -Iz echo "Hi there z"将输出：
Hi there 1
Hi there 2
...
你好 1
你好 2
...
回答by Wilson Silva
If you're using the zsh shell:
如果您使用的是 zsh shell：
repeat 10 { echo 'Hello' }
Where 10 is the number of times the command will be repeated.
其中 10 是命令重复的次数。
回答by Ole Tange
Using GNU Parallel you can do:
使用 GNU Parallel 您可以执行以下操作：
parallel some_command ::: {1..1000}
If you do not want the number as argument and only run a single job at a time:
如果您不想将数字作为参数并且一次只运行一个作业：
parallel -j1 -N0 some_command ::: {1..1000}
Watch the intro video for a quick introduction: https://www.youtube.com/playlist?list=PL284C9FF2488BC6D1
观看介绍视频以进行快速介绍：https: //www.youtube.com/playlist?list=PL284C9FF2488BC6D1
Walk through the tutorial (http://www.gnu.org/software/parallel/parallel_tutorial.html). You command line with love you for it.
完成教程 ( http://www.gnu.org/software/parallel/parallel_tutorial.html)。你爱你的命令行。
回答by steel
A simple function in the bash config file (~/.bashrcoften) could work well.
bash 配置文件中的一个简单函数（~/.bashrc通常）可以很好地工作。
function runx() {
for ((n=0;n<;n++))
do ${*:2}
done
}
Call it like this.
这样称呼。
$ runx 3 echo 'Hello world'
Hello world
Hello world
Hello world
回答by James Scriven
xargsis fast:
xargs为快：
#!/usr/bin/bash
echo "while loop:"
n=0; time while (( n++ < 10000 )); do /usr/bin/true ; done
echo -e "\nfor loop:"
time for ((n=0;n<10000;n++)); do /usr/bin/true ; done
echo -e "\nseq,xargs:"
time seq 10000 | xargs -I{} -P1 -n1 /usr/bin/true
echo -e "\nyes,xargs:"
time yes x | head -n10000 | xargs -I{} -P1 -n1 /usr/bin/true
echo -e "\nparallel:"
time parallel --will-cite -j1 -N0 /usr/bin/true ::: {1..10000}
On a modern 64-bit Linux, gives:
在现代 64 位 Linux 上，给出：
while loop:
real 0m2.282s
user 0m0.177s
sys 0m0.413s
for loop:
real 0m2.559s
user 0m0.393s
sys 0m0.500s
seq,xargs:
real 0m1.728s
user 0m0.013s
sys 0m0.217s
yes,xargs:
real 0m1.723s
user 0m0.013s
sys 0m0.223s
parallel:
real 0m26.271s
user 0m4.943s
sys 0m3.533s
This makes sense, as the xargscommand is a single native process that spawns the /usr/bin/truecommand multiple time, instead of the forand whileloops that are all interpreted in Bash. Of course this only works for a single command; if you need to do multiple commands in each iteration the loop, it will be just as fast, or maybe faster, than passing sh -c 'command1; command2; ...'to xargs
这是有道理的，因为该xargs命令是一个单独的本地进程，它/usr/bin/true多次生成命令，而不是在 Bash 中全部解释的for和while循环。当然，这只适用于单个命令；如果您需要在每次迭代循环中执行多个命令，它将与传递sh -c 'command1; command2; ...'给 xargs一样快，或者可能更快
The -P1could also be changed to, say, -P8to spawn 8 processes in parallel to get another big boost in speed.
该-P1也可以改变，比方说，-P8产卵并行8个流程，以获得速度的另一大助力。
I don't know why GNU parallel is so slow. I would have thought it would be comparable to xargs.
我不知道为什么 GNU 并行这么慢。我原以为它可以与 xargs 相媲美。
回答by Paused until further notice.
Another form of your example:
您示例的另一种形式：
n=0; while (( n++ < 10 )); do some_command; done
回答by firejox
xargs and seq will help
xargs 和 seq 会有所帮助
function __run_times { seq 1 | { shift; xargs -i -- "$@"; } }
the view :
风景 ：
abon@abon:~$ __run_times 3 echo hello world
hello world
hello world
hello world
回答by bta
For one, you can wrap it up in a function:
一方面，您可以将其封装在一个函数中：
function manytimes {
n=0
times=
shift
while [[ $n -lt $times ]]; do
$@
n=$((n+1))
done
}
Call it like:
像这样称呼它：
$ manytimes 3 echo "test" | tr 'e' 'E'
tEst
tEst
tEst
