关于如何在Linux中与另一个Shell交互使用Shell的一些问题

Question

This post is about some automation tasks, and also to satisfy my curiosity.

Is this scenario possible, can anyone offer any practical pointers?

Run a shell script

shell_exec(bash script);

Bash script like:

• Run a shell;
• read file for input;
• pass input to shell;
• fetch result from shell;
• write to another file for output.
• Keep in infinite loop.

Write input commands to file for example:

• wait few seconds
• read output file for result
• depending on output, write new input commands to file
• the loop continues.

Answer 1

I'm going to leave a shameless link to a post where I demonstrate doing this, "expect in php": http://codehackit.blogspot.be/2012/04/automating-command-line-scripts-in-php.html

Basically it's just a wrapper around proc_open(), which returns FDs for writing and reading to another processes stdin/stdout. http://php.net/manual/en/function.proc-open.php

Answer 2

In order to avoid problems with partial reads and writes (due to io buffering and races), you may want to consider using a directory the in/out-box like so:

1. Create your command files in the dir with "temporary" names (eg "cmd_`date +%s`.txt.tmp")
2. When you're done writing to a given command file, close it (to flush the buffers), then rename it to remove the ".tmp". Rename is atomic within a filesystem.
3. Have the consuming bash "daemon" only look at "cmd_*.txt" (not .tmp) and when it's done with a given command, either delete the cmd file or rename it to give it a ".done" suffix. (If you need multiple parallel worker daemons, you can probably even rename to ".processing" to "claim" a cmd while you work on it. Just be sure to check the return code of the rename when you do so to see if another worker out-raced you.)

Do likewise for the output files.