Bash – execute bash script inside .bashrc

bashbashrc

Hi I am curious if it is possible to execute a bash script inside bash rc. It would seem to create a infinite loop unless there was some way to tell it to not try and start a new shell.

Here is an example

bash_script.sh:

#!/bin/bash
echo Hello World

.bashrc

export HELLO_WORLD=$(bash_script.sh)

Best Answer

A script is executed by a non-interactive shell, while .bashrc is only automatically sourced by interactive shells.

There is a way to trigger an infinite loop, though. Every bash shell, interactive or not, checks if the variable BASH_ENV is set and, if so, uses its value as the name of a file to source. In this case, executing a bash script from this file would result in the infinite loop, so are must be taken. In practice, though, this script would (as its name suggests) simply be used to set environment variables for use by the shell, not execute arbitrary code.

Related Solutions

Bash – Modify $READLINE_LINE and $READLINE_POINT values inside bash script

Just by the same reason why this won’t work:

$ export a=1
$ bash -c 'echo $a; let a++'
1
$ echo $a
1

Environment variables are heritable, not shareable. Since autocomplete.sh is executed as a new child process, it can read all parent’s variables, but can‘t push new values back.

To modify READLINE_LINE and READLINE_POINT you have to execute your autocomplete in the same process – source and functions will help you.

# autocomplete.sh
# should be sourced from ~/.bashrc or something

autocomplete() {
    echo $READLINE_LINE $READLINE_POINT
    EXPANSION=($(magical_autocomplete $READLINE_LINE))
    #we store the desired value for the line in ${EXPANSION[0]}
    [[ ${#EXPANSION[@]} -gt 1 ]] && echo ${EXPANSION[@]:1}

    READLINE_LINE=${EXPANSION[0]}
    READLINE_POINT=${#READLINE_LINE}
}

Binding:

if [[ -s "$HOME/.bashrc.d/autocomplete.sh" ]]; then
    source "$HOME/.bashrc.d/autocomplete.sh" 
    bind -x '"\t" : autocomplete'
fi

Bash – How to See the Exact Command Line Being Executed

I knew I was grasping at straws, but UNIX never fails!

Here's how I managed it:

bash$ gdb --pid 8909
...
Loaded symbols for /lib/i386-linux-gnu/i686/cmov/libnss_files.so.2
0xb76e7424 in __kernel_vsyscall ()

Then at the (gdb) prompt I ran the command, call write_history("/tmp/foo") which will write this history to the file /tmp/foo.

(gdb) call write_history("/tmp/foo")
$1 = 0

I then detach from the process.

(gdb) detach
Detaching from program: /bin/bash, process 8909

And quit gdb.

(gdb) q

And sure enough...

bash$ tail -1 /tmp/foo
while true ; do echo 1 ; echo 2>/dev/null ; sleep 30 ; done

For easy future re-use, I wrote a bash script, automating the process.

Best Answer

Related Solutions

Bash – Modify $READLINE_LINE and $READLINE_POINT values inside bash script

Bash – How to See the Exact Command Line Being Executed

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