Enter and Exit subprocess from Shell Script

Question

I am trying to enter irb from a shell script, do something, and then return to the shell script.

How can I do this?

#!/bin/bash
#example_app

# Some shell instructions here
irb
four = 2 + 2
exit
echo "This text is not reached and the process hangs open"

NOTE: I should not try to load irb to enter static code, I agree with you guys. I didn't think about what I was doing. I was interacting with an AWS library and I tried to carry that same philosophy into automating this without thinking twice about it.

Are you looking for something like eval or do you actually need a new process? — Yet Another Geek
– Yet Another Geek, Commented May 2, 2012 at 19:18
I'm not sure what you're asking. Judging by the irb man page, you might be looking for something like expect. — Tim Pote
– Tim Pote, Commented May 2, 2012 at 19:21
I am trying to execute a series of ruby commands from a shell script that work perfectly from ruby console if I manually enter irb. An extremely simplified explanation of what I need is [a shell script that can enter irb, do something, and return to the shell script to echo "Done!"] — Dru
– Dru, Commented May 2, 2012 at 19:23
why you have to do it in irb ? It is supposed to be interacive. Why not run ruby directly ? ruby <script file> — dpp
– dpp, Commented May 2, 2012 at 19:30
ruby also has a -e option, you could also do ` ruby -e 'four = 2 + 2' -e 'puts four' ` from your bash shell if your code is only few lines. — dpp
– dpp, Commented May 2, 2012 at 19:49

Matheus Moreira · Accepted Answer · 2012-05-02 19:59:21Z

2

You can pass a here document to irb:

irb <<SCRIPT
  four = 2 + 2
  puts four
SCRIPT

However, I don't think that will accomplish what you are trying to do. Here is the output:

Switch to inspect mode.
  four = 2 + 2
4
  puts four
4
nil

It is similar to bash -x. Why not simply use plain old ruby for this?

ruby <<SCRIPT
  four = 2 + 2
  puts four
SCRIPT
4

There is no need to spawn an interactive shell if you aren't going to interact with it.

edited May 2, 2012 at 19:59

answered May 2, 2012 at 19:52

Matheus Moreira

17.1k3 gold badges73 silver badges112 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Community · Accepted Answer · 2017-05-23 12:27:56Z

0

I think you want the answer explained from fork and exec in bash essentially:

function_to_fork() { irb }

function_to_fork &

that may not work if you want some interaction there to influence the parent process or for the parent process to wait.

My comment below didn't format very well:

With the following program I was able to achieve:

#!/bin/bash
# irbb.sh
irb
echo "here"

$ ./irbb.sh 
>> four = 2 + 2
=> 4
>> exit
here

edited May 23, 2017 at 12:27

CommunityBot

11 silver badge

answered May 2, 2012 at 19:26

Ecuageo

265 bronze badges

6 Comments

Tim Pote Over a year ago

I don't think this answers the question at all. The OP essentially wants to run some commands in another shell, then return to his script in sequence, not in parallel.

Dru Over a year ago

I tried what you suggested. The process does not hang open as before, but shell commands after the fork are not getting executed and the code inside the fork doesn't seem to be getting executed. (The actual ruby code, involves storing files. I've tested this manually and it works. That's how I'm able to isolate it to this shell script.)

Ecuageo Over a year ago

With the following program I was able to achieve: #!/bin/bash # irbb.sh irb echo "here" $ ./irbb.sh >> four = 2 + 2 => 4 >> exit here

Tim Pote Over a year ago

@Ecuageo Post it in your answer.

Tim Pote Over a year ago

He doesn't want to enter that stuff by hand, he want's that input automated.

|

Collectives™ on Stack Overflow

Enter and Exit subprocess from Shell Script

2 Answers 2

Comments

6 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

6 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related