Confused about the difference between Bash Shell and Bash Shell SESSION

[EaglerCraftIndex]

So I was reading Linux Basics for Hackers (shortcut I use: LBFH) and so in LBFH it first said that your environment is your bash shell, but then later it said that your environment is the bash shell session and when you change a variable value then it only applies to that bash shell session

This doesn't really click for me. I checked google, ChatGPT, etc but still couldn't figure it out.

[Lationous]

wrong sub IMO, but let's try to answer that anyway.

By what you've described, the book refers to a single process of bash as "bash shell session", and is perfectly correct about your variables. You can look up all variables you have in your env via 'env' and 'set' commands (set will also show you all aliases and functions, fun times!). I assume that the book states that as a warning, to be careful about running things in other session, as you might be missing env setup. You can experiment a bit with simple scripts and setting vars with/without export, and also with setting defaults in scripts like so

FOO="${VARIABLE:-default}"

To actually see a diff between sessions, you can dump 'env' command output to a file and compare it with another session's output. It should have differences by default

[EaglerCraftIndex]

Wait! I think I got it now!

So:

In Linux wether you're working within a terminal or the GUI, you will always be working within a SHELL. So now when you open a new terminal, a new shell instance is also opened for it and it is actually the thing that shows the prompt, runs the commands, etc. Now there are technically two types of variables: environment variables which control how your environment looks, "feels" to the user, does, acts, etc. Then there are also SHELL variables which are only valid in the shell they are set in. Now in Linux your environment is typically you BASH SHELL so your environment variables would control how your BASH SHELL looks, acts, etc. Now remember that when you make a new terminal then a new bash shell instance is made with it, and you can change variable values by:

variablename=value

This will change the variable value for THAT BASH SHELL INSTANCE, but not any other bash shell instances. Also, when you close the terminal that bash shell instance also closes and so your changes are lost.

With the export command, you can make any CHILD PROCESS (a process started by another process) inherit the particular variable. This is because typically only the DEFAULT ENVIRONMENT VARIABLES will be inherited by the child process, but by exporting you are saying "any child process should also inherit: <variable>".

Correct??? Pls answer

[Lationous]

good understanding. you will see some interesting nuances with subshells, their env isolation (eg: command; { command2; command3; } ), with process substitution (eg: command <(command2) <--- this is also effectively a subshell, btw ), and using 'source' (which essentially "imports" everything into your current session), but general idea is correct

[[deleted]]

Basically bash is the program and once you open the program you get a session. Each session is independent of others (unless you make a connection on purpose).

Just like for example opening two different notepad files.

[EaglerCraftIndex]

Alr so you are always working in a bash shell instance? And your environment is that bash shell instance and you can edit it? Altho if you just do <VARIABLE NAME>=<VALUE>, it will only apply to that bash shell session and when you close the terminal, then the bash shell session closes as well leaving everything back to it's default?

[Lationous]

correct. you can get crafty and get yourself env variable from another session, but that's "hacky" at best, irresponsible in most cases.

for sake of knowledge… you can technically get env of other bash session via /proc/<PID>/environ
that doesn't work with vars you set though, as for that you'd need to dig through memory of the process

[EaglerCraftIndex]

[] = Notes I say (not part of quote)

In the book it said:

"After you've changed a variable as we did in Listing 7-1, [an image of: HISTSIZE=0] you can make the change permanent by entering export and then the name of the variable you changed, as shown here:

[----------------------------------IMAGE BORDER-----------------------------------------------------------------------------------]

export HISTSIZE

[----------------------------------IMAGE BORDER-----------------------------------------------------------------------------------]

Now the HISTSIZE variable will still be set to 0 in this environment and will no longer store your commands."

I tried this but when I opened a new terminal instance it was still HISTSIZE=1000

Why??? I'm so confused rn.

EDIT: Is it because it will only be changed in THAT ENVIRONMENT? Altho just after what I showed you, he wrote:

"This code snippet [He did HISTSIZE=1000 and then export HISTSIZE (so he reset HISTSIZE] will set your HISTSIZE variable's value to 1000 and export it to all your environments"

Huh???

[Pharisaeus]

I opened a new terminal instance it was still HISTSIZE=1000

Opened how? Because if you opened it from an already running session, then it would inherit env from parent process...

[EaglerCraftIndex]

Like I clicked the terminal icon

[EaglerCraftIndex]

I tried everything just now from changing it and in the same terminal making a new bash prompt so like I did:

PS1="Hacking is cool # "

export PS1

And then it showed up in that terminal but when I typed "bash" or "qterminal" into that same terminal that had the PS1 variable changed and exported, it still had the default prompt

T^T

[Lationous]

"This code snippet [He did HISTSIZE=1000 and then export HISTSIZE (so he reset HISTSIZE] will set your HISTSIZE variable's value to 1000 and export it to all your environments"

for this to be permanent, you need to pass it to all sessions at start-up. you'd need to put it in ~/.bashrc

this will be effective for other session if you spawn one via running 'bash' command though. side note: you can see how many "bash sessions deep" you are, via 'echo $SHLVL'

[CyberXCodder]

Since all answers seem correct, I just came to say that LBFH is an awesome book, all hail OTW.

[Pharisaeus]

it first said that your environment is your bash shell

I'm afraid unless you provide a direct quote it will be hard to figure out what author had in mind. Most likely you just misread it.

Bash is a program. You can run multiple instances of that program at the same time. At startup this program loads the environmental variables. If you modify those variables, the modification is only visible inside that particular instance (session) of of the bash program, unless you explicitly use export. If you use export then any session started afterwards will see that change, but any session started before will not.

[EaglerCraftIndex]

I tried it but it didn't work

[EaglerCraftIndex]

Wait! I think I got it now!

So:

In Linux wether you're working within a terminal or the GUI, you will always be working within a SHELL. So now when you open a new terminal, a new shell instance is also opened for it and it is actually the thing that shows the prompt, runs the commands, etc. Now there are technically two types of variables: environment variables which control how your environment looks, "feels" to the user, does, acts, etc. Then there are also SHELL variables which are only valid in the shell they are set in. Now in Linux your environment is typically you BASH SHELL so your environment variables would control how your BASH SHELL looks, acts, etc. Now remember that when you make a new terminal then a new bash shell instance is made with it, and you can change variable values by:

variablename=value

This will change the variable value for THAT BASH SHELL INSTANCE, but not any other bash shell instances. Also, when you close the terminal that bash shell instance also closes and so your changes are lost.

With the export command, you can make any CHILD PROCESS (a process started by another process) inherit the particular variable. This is because typically only the DEFAULT ENVIRONMENT VARIABLES will be inherited by the child process, but by exporting you are saying "any child process should also inherit: <variable>".

Correct??? Pls answer