为什么我不能使用Expect脚本启动Redis？

Question

I guess there must be a simple reason why I can't start redis like this

---- update -----

After @larsks answered my question I realize it is this one that cause my confusion "You end it with an interact statement, which conncets your console to the stdin/stdout of the process you spawned. The redis-server program is not interactive: it doesn't accept any console input."

I check the code again and found it was this code that made me think the process was stuck

#!/usr/bin/expect -f
spawn redis-server
expect "The server is now ready to accept connections"
interact
spawn redis-cli
expect ">"
...

I never saw redis-cli run.

But if I change to

#!/usr/bin/expect -f
spawn redis-server
expect "The server is now ready to accept connections"
spawn redis-cli
expect ">"
...
interact //put it in the end.

It works as I expected.

BTW the reason I use expect here is first to make sure redis server starts then delete some keys.

Answer 1

What do you expect the first example to do? You end it with an interact statement, which connets your console to the stdin/stdout of the process you spawned. The redis-server program is not interactive: it doesn't accept any console input. When you run redis-server , it will get as far as...

1135:M 18 Nov 13:59:51.634 * Ready to accept connections

...and then it stops, waiting for redis clients to connect and operate on it. Also, note that the Redis version I'm using ends with Ready to accept connections rather than The server is now ready to accept connections , so I'll be using that in the following examples.

We can add a puts command to the expect script to see that it isn't actually getting stuck anywhere. If I run the following:

#!/usr/bin/expect -f
spawn redis-server
expect "Ready to accept connections"
puts "redis is running"
interact

I get as output:

spawn redis-server
1282:C 18 Nov 14:03:33.123 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
1282:C 18 Nov 14:03:33.123 # Redis version=4.0.10, bits=64, commit=00000000, modified=0, pid=1282, just started
[...]
1282:M 18 Nov 14:03:33.124 * Ready to accept connections
redis is running

So we can see that it's not getting stuck at the spawn statement, nor even at the expect statement.

What's not clear from your question is why you're even using expect in this situation, since redis-server is not an interactive program and does not produce any prompts that require automation.