庆典的重定向输出回路 [英] Redirecting output of bash for loop

问题描述

我有一个简单的bash命令看起来像

I have a simple BASH command that looks like

for i in `seq 2`; do echo $i; done; > out.dat

在此运行的输出以次2 是输出到终端，没有什么是输出到数据文件（out.dat）

When this runs the output of seq 2 is output to the terminal and nothing is output to the data file (out.dat)

我期待标准输出重定向到out.dat像它只需运行命令以次2 - ; out.dat

I am expecting standard out to be redirected to out.dat like it does simply running the command seq 2 > out.dat

推荐答案

删除您的分号。

for i in `seq 2`; do echo "$i"; done > out.dat

建议

也由Fredrik作为皮赫尔建议，尽量不要使用外部二进制文件不需要时，或至少在几乎没有：

Also as suggested by Fredrik Pihl, try not to use external binaries when they are not needed, or at least when practically not:

for i in {1..2}; do echo "$i"; done > out.dat
for ((i = 1; i <= 2; ++i )); do echo "$i"; done > out.dat
for i in 1 2; do echo "$i"; done > out.dat

此外，，可能会导致路径扩展词小心的输出。

for A in $(echo '*'); do echo "$A"; done

将显示您的文件，而不仅仅是文字 * 。

$（）也被推荐为Bash和POSIX壳命令替换比反引号（更清晰的语法`），并支持嵌套。

$() is also recommended as a clearer syntax for command substitution in Bash and POSIX shells than backticks (`), and it supports nesting.

该清洁解决方案，以及用于读取输出变量

The cleaner solutions as well for reading output to variables are

while read VAR; do
    ...   
done < <(do something)

和

read ... < <(do something)  ## Could be done on a loop or with readarray.

for A in "${ARRAY[@]}"; do
    :
done

使用的printf也可以是相对于所述预定的功能更简单的替代方法：

Using printf can also be an easier alternative with respect to the intended function:

printf '%s\n' {1..2} > out.dat

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