The differences between a login shell and interactive shell?

不念不忘少年蓝@ 2022-05-15 17:17 224阅读 0赞

> An interactive shell is one started without non-option arguments, unless -s is specified, without specifying the -c option, and whose input and error output are both connected to terminals (as determined by isatty(3)), or one started with the -i option.

> An interactive shell generally reads from and writes to a user’s terminal.

**A login shell** is a shell where you login. You can recognize a login shell from a ps -f listing, it will have a hyphen at the start of the program name, for example:

root      3561  3553  0 09:38 pts/0    00:00:00 -bash
    qa        7327  3432  0 10:46 pts/1    00:00:00 -bash

**An interactive shell** is one which reads commands from it’s standard-input, usually a terminal.

For example, if you login to bash using an xterm or terminal emulator like putty, then the session is both a login shell and an interactive one. If you then type bash then you enter an interactive shell, but it is not a login shell.

If a shell script (a file containing shell commands) is run, **then it is neither a login shell nor an interactive one.**

**Start-up files are highly tailorable in bash:**

When a login bash shell is invoked, then /etc/profile is sourced (executed in the current environment). After that, three files are checked for existence. The checks for these files are done in this order:

*  if **/etc/profile** exists, source (run) it
 *  if **~/.bash\_profile** exists, source (run) it
 *  if **~/.bash\_login** exists, source (run) it
 *  if **~/.profile** exists, source (run) it

Once a match is found, the other files are ignored, even if they exist. The **/etc/bashrc** file might be used by both the **~/.bash\_profile** and the **~/.bashrc** files. That would mean that the /etc/bashrc file is sourced on all interactive invocations of bash, whether it is a login or non-login shell.

So, the .bashrc file is also run every time you request a new interactive shell. This does not include a shell script. Normally variables, aliases or functions are placed in this file.

Bash shell scripts read a different file if suitably instructed. If the user defines (usually in their own **.bash\_profile**) a variable **BASH\_ENV** which contains a filename, scripts will read this. If this variable is not set (and exported) then bash scripts will not read any startup files.

*原文链接*  
[https://stackoverflow.com/questions/18186929/what-are-the-differences-between-a-login-shell-and-interactive-shell\#][https_stackoverflow.com_questions_18186929_what-are-the-differences-between-a-login-shell-and-interactive-shell]

[https_stackoverflow.com_questions_18186929_what-are-the-differences-between-a-login-shell-and-interactive-shell]: https://stackoverflow.com/questions/18186929/what-are-the-differences-between-a-login-shell-and-interactive-shell#