What do the characters in the bash $ environment variable mean - mean?

Question

I have looked at some of the .bashrc and .profile scripts that come with various Linux distributions, and I see that sometimes they check $- .

Here is one in Ubuntu

 case $- in *i*) ;; *) return;; esac 

In this case, it checks for the presence of the "i" flag to see if the current shell is interactive.

My current session gives me the following:

 # echo $- himBH 

What do other flags / options mean? Is there an exhaustive list somewhere?

Answer 1

From man bash :

-

Expands to the current option flags specified during the call, with the set builtin command or those set by the shell itself (for example, the -i option).

So, these are the current parameters that control the behavior of the shell. In particular:

• h : The location of the binary cache in $PATH . Speeds up execution, but fails if you move binary files during a shell session.
• i : the current shell is interactive
• m : Job management enabled
• B : Bracketing extension enabled
• h : Replacing stories like !-1

Answer 2

They mean different things. Each letter corresponds to the option given for bash. for example, “i” means that the shell is interactive (so the sample code you gave is a test to see if it is an interactive shell or not).

A complete list is available on the bash manual page. Look for "set" - here is the first line:

 set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]