BASH：如何对管道中的数字执行算术运算
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BASH: how to perform arithmetic on numbers in a pipe
提问by brice
I am getting a stream of numbers in a pipe, and would like to perform some operations before passing them on to the next section, but I'm a little lost about how I would go about it without breaking the pipe.
我在管道中获得了一个数字流，并且想在将它们传递到下一部分之前执行一些操作，但是我对如何在不破坏管道的情况下进行操作有点迷茫。
for example
例如
> echo "1 2 3 4 5" | some command | cat
1 4 9 16 25
>
Would you have any ideas on how to make something like this work? The actual operation I want to perform is simply adding one to every number.
你对如何制作这样的作品有什么想法吗？我想要执行的实际操作只是将每个数字加一。
采纳答案by Matthew Flaschen
echo 1 2 3 4 5|{
read line;
for i in $line;
do
echo -n "$((i * i)) ";
done;
echo
}
The {} creates a grouping. You could instead create a script for that.
{} 创建一个分组。您可以为此创建一个脚本。
回答by tokland
I'd write:
我会写：
echo "1 2 3 4 5" | {
for N in $(cat); do
echo $((N ** 2))
done | xargs
}
We can think of it as a "map" (functional programming). There are a lot of ways of writing a "map" function in bash (using stdin, function args, ...), for example:
我们可以将其视为“地图”（函数式编程）。有很多方法可以在 bash 中编写“map”函数（使用 stdin、函数参数等），例如：
map_stdin() {
local FUNCTION=
while read LINE; do
$FUNCTION $LINE
done
}
square() { echo "$(( * ))"; }
$ echo "1 2 3 4 5" | xargs -n1 | map_stdin square | xargs
1 4 9 16 25
回答by aoakenfo
echo 1 2 3 4 5 | xargs -n 1 expr -1 +
回答by lasseoe
Or..
或者..
echo "1 2 3 4 5" | xargs -n 1 | while read number
do
echo $((number * number))
done
回答by tilo
echo 1 2 3 4 5 | xargs -n 1 bash -c 'echo $((*))' args
回答by Niko
Using awk is another solution, which also works with floats
使用 awk 是另一种解决方案，它也适用于浮点数
echo "1 2 3 4 5" | xargs -n1 | awk '{print ^2}' | xargs
or use a loop
或使用循环
for x in 1 2 3 4 5; do echo $((x**2)); done | xargs
for x in $(echo "1 2 3 4 5"); do echo $x^2 | bc; done | xargs # alternative solution
for x in $(seq 5); do python -c "print($x**2)"; done | xargs # alternative solution but slower than the above
# or make it neat by defining a function to do basic math in bash, e.g.:
calc() { awk "BEGIN{print $*}"; }
for x in $(seq 5); do calc $x^2; done | xargs
回答by SiggyF
Or you can pipe to expression to bc:
或者您可以通过管道将表达式传递给 bc：
echo "1 2 3 4 5" | (
read line;
for i in $line;
do
echo $i^2 | bc;
done;
echo
)
回答by Amber
If you prefer Python:
如果你更喜欢 Python：
#!/bin/python
num = input()
while num:
print(int(num) + 1) # Whatever manipulation you want
try:
num = input()
except EOFError:
break
回答by Bluu
xargs, xargs, xargs
xargs, xargs, xargs
echo 1 2 3 4 5 | xargs -n1 echo | xargs -I NUMBER expr NUMBER \* NUMBER | xargs
Or, go parallel:
或者，并行：
squareit () { expr \* ; }
export -f squareit
echo 1 2 3 4 5 | xargs -n1 | parallel --gnu squareit | xargs
Which would be way simpler if you passed your pipe as a standard set of args:
如果您将管道作为标准参数集传递，这会更简单：
parallel --gnu "expr {} \* {}" ::: $(echo 1 2 3 4 5) | xargs
Or even:
甚至：
parallel --gnu "expr {} \* {}" ::: 1 2 3 4 5 | xargs
Really worth taking a look at the examples in the doc: https://www.gnu.org/software/parallel/man.html
确实值得一看文档中的示例：https: //www.gnu.org/software/parallel/man.html
回答by Aleks-Daniel Jakimenko-A.
Yoi might like something like this:
Yoi 可能喜欢这样的东西：
echo "1 2 3 4 5" | perl -ne 'print $_ ** 2, " " for split / /, $_'
or even like this:
甚至像这样：
echo "1 2 3 4 5" | perl -ne 'print join " ", map {$_ ** 2} split / /, $_'
