为什么“& ;"在bash中无效的语法？ [英] Why is "& ;" invalid syntax in bash?

问题描述

我试图在终端上运行一个for循环，我想把每个迭代发送到后台进程，这样所有的循环都可以同时运行。

以下是一个一个运行的命令

  * .sra;做fastq-dump --split-files $ i;完成＃;只有
  

我已经突出了分号。

要同时运行这个工程

  for i in * .sra;做fastq-dump --split-files $ i&完成＃&只有
  

但是这个错误

  for i in * .sra;做fastq-dump --split-files $ i& ;完成＃&; 
  

如果有人解释这里发生了什么，那将会很好。我知道这应该写在一个合适的缩进shell脚本的方式，但有些时候，我只有这个命令来运行。

谢谢

解决方案

& 和; 命令。

不能写& ; 不止可以写; ; 或& & ，因为语言只允许命令终止一次（并且不允许零字列表作为命令）。

< hr>

因此：用于i in * .src;做fastq-dump --split-files$ i&完成完全正确，并且不需要额外的; 。

I am trying to run a for loop on the terminal where I want to send each iteration to background process so that all of them run simultaneously.

Following is the command running one by one

for i in *.sra; do fastq-dump --split-files $i ; done  # ";" only

I have highlighted the semicolon.

To run simultaneously this works

for i in *.sra; do fastq-dump --split-files $i & done  # "&" only

but this gives an error

for i in *.sra; do fastq-dump --split-files $i & ; done  # "& ;"

It would be nice if some one explains what is going on here. I know this should be written in a shell script way with proper indentation, but some times I only have this command to run.

Thanks

解决方案

& and ; both terminate the command that precedes them.

You can't write & ; any more than you could write ; ; or & &, because the language only allows a command to be terminated once (and doesn't permit a zero-word list as a command).

---

Thus: for i in *.src; do fastq-dump --split-files "$i" & done is perfectly correct as-is, and does not require an additional ;.

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