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41.2 Interactive Inferior Shell

To run a subshell interactively, putting its typescript in an Emacs buffer, 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 face comint-highlight-prompt. This makes it easier to see previous input lines in the buffer. See section Using Multiple Typefaces.

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-nil. 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 ‘.emacs’ file can override either or both of these default initializations.

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 section Coding Systems for Interprocess Communication.

Emacs sets the envitonment variable INSIDE_EMACS to t in the subshell. Programs can check this variable to determine whether they are running inside an Emacs subshell.

Emacs also sets the EMACS environment variable to t if it is not already defined. Warning: This environment variable is deprecated. Programs that check this variable should be changed to check INSIDE_EMACS instead.


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