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

Question

I\'ve been looking through some of the .bashrc and .profile scripts that come with various Linux distros and am seeing that sometimes they check $-.

Her

Answer 1

They mean various things. Each letter corresponds to an option being set for bash. eg, "i" means that the shell is interactive (so the code sample you gave is a test to see if it's an interactive shell or not).

A full list is available in the bash man page. Look for "set" - here's the first line:

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

Answer 2

From man bash:

-

Expands to the current option flags as specified upon invocation, by the set builtin command, or those set by the shell itself (such as the -i option).

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

• h: Cache location of binaries in the $PATH. Speeds up execution, but fails if you move binaries around during the shell session.
• i: The current shell is interactive
• m: Job control is enabled
• B: Brace expansion is enabled
• H: History substitution like !-1