Dash (-) in front of bash

If I examine my bash shell in an OS X (10.6.4) terminal, such as by typing echo $0, there is a dash in front of my shell, like this: -bash. What does this dash mean?

Solution 1:

It means that bash is invoked as a login shell.

man bash says:

A login shell is one whose first character of argument zero is a -, or one started with the --login option.

When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable. The --noprofile option may be used when the shell is started to inhibit this behavior.

When a login shell exits, bash reads and executes commands from the file ~/.bash_logout, if it exists.

You'll find login -pf in your ps output, which starts a login shell by default.

Try running login -pf and login -pfl and see the difference. man login describes the difference:

-l Tells the program executed by login that this is not a login session (by convention, a login session is signalled to the program with a hyphen as the first character of argv[0]; this option disables that), and prevents it from chdir(2)ing to the user's home directory. The default is to add the hyphen (this is a login session).