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I want to run a bash subshell, (1) run a few commands, (2) and then remain in that subshell to do as I please. I can do each of these individually:

  1. Run command using -c flag:

    $> bash -c "ls; pwd; <other commands...>"
    

    however, it immediately returns to the "super" shell after the commands are executed. I can also just run an interactive subshell:

  2. Start new bash process:

    $> bash
    

    and it won't exit the subshell until I say so explicitly... but I can't run any initial commands. The closest solution I've found is:

    $> bash -c "ls; pwd; <other commands>; exec bash"
    

    which works, but not the way I wanted to, as it runs the given commands in one subshell, and then opens a separate one for interaction.

I want to do this on a single line. Once I exit the subshell, I should return back to the regular "super"shell without incident. There must be a way~~

NB: What I am not asking...

  1. not asking where to get a hold of the bash man page
  2. not asking how to read initializing commands from a file... I know how to do this, it's not the solution I'm looking for
  3. not interested in using tmux or gnu screen
  4. not interested in giving context to this. I.e., the question is meant to be general, and not for any specific purpose
  5. if possible, I want to avoid using workarounds that sort of accomplish what I want, but in a "dirty" way. I just want to do this on a single line. In particular, I don't want to do something like xterm -e 'ls'
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I can imagine an Expect solution, but it's hardly the one-liner you want. In what way is the exec bash solution unsuitable for you? –  glenn jackman Mar 9 '12 at 16:21
    
@glennjackman sorry, I'm not familiar with the jargon. What is an "Expect solution"? Also, the exec bash solution involves two separate subshells. I want one continuous subshell. –  SABBATINI Luca Mar 9 '12 at 19:18
    
The beauty of exec is that it replaces the first subshell with the second, so you're only left 1 shell below the parent. If your initialization commands set environment variables, they will exist in the exec'ed shell. –  glenn jackman Mar 9 '12 at 19:45

3 Answers 3

This can be easily done with temporary named pipes:

bash --init-file <(echo "ls; pwd")

Credit for this answer goes to the comment from Lie Ryan. I found this really useful, and it's less noticeable in the comments, so I thought it should be its own answer.

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You can do this in a roundabout way with a temp file, although it will take two lines:

echo "ls; pwd" > initfile
bash --init-file initfile
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Now to wrap that into a function! –  cjc Mar 9 '12 at 16:56
    
For a nice effect you can make the temp file remove itself by including rm $BASH_SOURCE in it. –  Eduardo Ivanec Mar 9 '12 at 17:05
    
Eduardo, thank you. That's a nice solution, but... are you saying that this can't be done without having to fiddle with file I/O. There's obvious reasons why I would prefer to keep this as a self contained command, because the moment files come into the mix I'll have to start worrying about how to make random temp-files and then, as you mentioned, deleting them. It just requires so much more effort this way if I want to be rigorous. Hence the desire for a more minimalistic, elegant solution. –  SABBATINI Luca Mar 9 '12 at 17:20
    
Use the mktemp utility to create a unique temp file. –  cjc Mar 9 '12 at 17:39
4  
This is an old question, but Bash can create temporary named pipes by using the following syntax: bash --init-file <(echo "ls; pwd"). –  Lie Ryan Feb 13 at 14:59

The "Expect solution" I was referring to is programming a bash shell with the Expect programming language:

#!/usr/bin/env expect
set init_commands [lindex $argv 0]
set bash_prompt {\$ $}              ;# adjust to suit your own prompt
spawn bash
expect -re $bash_prompt {send -- "$init_commands\r"}
interact
puts "exiting subshell"

You'd run that like: ./subshell.exp "ls; pwd"

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