To run a subshell interactively, use M-x shell. This creates (or reuses) a buffer named ‘*shell*’ and runs a subshell with input coming from and output going to that buffer. That is to say, any “terminal output” from the subshell goes into the buffer, advancing point, and any “terminal input” for the subshell comes from text in the buffer. To give input to the subshell, go to the end of the buffer and type the input, terminated by <RET>.
Emacs does not wait for the subshell to do anything. You can switch windows or buffers and edit them while the shell is waiting, or while it is running a command. Output from the subshell waits until Emacs has time to process it; this happens whenever Emacs is waiting for keyboard input or for time to elapse.
Input lines, once you submit them, are displayed using the face
comint-highlight-input, and prompts are displayed using the
comint-highlight-prompt. This makes it easier to see
previous input lines in the buffer. See Faces.
To make multiple subshells, you can invoke M-x shell with a prefix argument (e.g. C-u M-x shell), which will read a buffer name and create (or reuse) a subshell in that buffer. You can also rename the ‘*shell*’ buffer using M-x rename-uniquely, then create a new ‘*shell*’ buffer using plain M-x shell. Subshells in different buffers run independently and in parallel.
The file name used to load the subshell is the value of the variable
explicit-shell-file-name, if that is non-
Otherwise, the environment variable ESHELL is used, or the
environment variable SHELL if there is no ESHELL. If the
file name specified is relative, the directories in the list
exec-path are searched; this list is initialized based on the
environment variable PATH when Emacs is started. Your init file
can override either or both of these default initializations.
(see Init File).
Emacs sends the new shell the contents of the file ~/.emacs_shellname as input, if it exists, where shellname is the name of the file that the shell was loaded from. For example, if you use bash, the file sent to it is ~/.emacs_bash. If this file is not found, Emacs tries to fallback on ~/.emacs.d/init_shellname.sh.
To specify a coding system for the shell, you can use the command C-x <RET> c immediately before M-x shell. You can also change the coding system for a running subshell by typing C-x <RET> p in the shell buffer. See Communication Coding.
Emacs sets the environment variable INSIDE_EMACS in the subshell to a comma-separated list including the Emacs version. Programs can check this variable to determine whether they are running inside an Emacs subshell.
Emacs also sets the EMACS environment variable (to
it is not already defined. Warning: This environment
variable is deprecated. Programs that check this variable should be
changed to check INSIDE_EMACS instead.