[Published in Open Source For You (OSFY) magazine, January 2016 edition.]

In this next article in the GNU Emacs series, we shall learn how to execute shell commands, run shells, use spell-checkers and abbreviations, and print from GNU Emacs.

Shell mode commands

You can run a shell command from GNU Emacs using the M-! shortcut. For example, typing ‘M-!’ will prompt you with the message ‘Shell command:’ in the minibuffer. If you then type ‘date’, it will produce the output ‘Tue Dec 8 21:19:24 IST 2015’ in the minibuffer. But, if you want the output to be inserted in the current buffer you can use the C-u M-! command sequence.

Consider the following poem that I wrote:

"Water, water everywhere
Little power and aid to spare
Really tough for us to bear
We will face it with Chennaites' flair.

Lakes and rivers overflowing everywhere
No road, rail or plane to go anywhere
People really are in big despair
But we will ride it with Chennaites' flair.

More storms are forecast to be aware
Nothing like this in 100 years to compare
Stay indoors and please do take care
And we will take it with Chennaites' flair."

Suppose I want to know the number of words used, I can mark the poem as a region in the GNU Emacs buffer, and execute a shell command for the region using M-| shortcut. It then prompts with the string ‘Shell command on region’, and when I type in ‘wc -w’ it returns ‘90’.

Shells

There are three shells available in GNU Emacs - shell, ansi-term and eshell. Using M-x shell will invoke a shell for you. This starts a new buffer with the name ‘shell’ in it. You can use all the GNU Emacs buffer commands in this window. For example, C-p will move the cursor up, and C-n will move the cursor down. In order to interrupt a current job in the shell buffer, you can use C-c C-c. If you want to suspend the current job, you can use C-c C-z. You can also clear the output from the previous command using C-c C-o. For example, the output of ‘ifconfig’ command is shown below:

/tmp $ ifconfig docker0
docker0   Link encap:Ethernet  HWaddr 56:84:7a:fe:97:99
          inet addr:172.17.42.1  Bcast:0.0.0.0  Mask:255.255.0.0
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
/tmp $

After executing ‘C-c C-o’, the previous command output gets cleared as shown below:

/tmp $ ifconfig docker0
 *** output flushed ***
/tmp $

You can move the cursor up to the previously executed commands using C-c C-p and move down using C-c C-n. You can also cycle backwards and forwards through the command history using the M-p and M-n shortcuts respectively. The C-c C-r shortcut moves to the first line of the output to the top of the window. You can move the cursor to the bottom of the window using C-c C-e. The C-r key binding allows you to search for a previously typed command from history.

The default shell is Bash, but, you can change it to use other shells like ksh, csh or zsh. You can open another shell buffer using C-u M-x shell. The new shell buffer will be called ’shell<2>". You can, of course, rename this buffer. You can thus open multiple shells to work inside GNU Emacs.

GNU Emacs also has a terminal emulator that you can invoke using M-x ansi-term. You can start a Bash session with this command to get the actual colours that you see in a terminal session. This is like a fallback shell if you do not want to use ‘M-x shell’. Eshell is the Emacs built-in shell written completely in Emacs Lisp (Elisp). You can start it using M-x eshell. The advantage of using this is that you can extend it, write your own customized Elisp functions and use it similar to shell scripting.

Screenshots of shell, ansi-term and eshells in GNU Emacs are shown in Figure 1, 2 and 3 respectively:

Spell check commands

You can check the spelling of a word by placing the cursor on it and using M-$ shortcut. For example, for the word ‘hte’, GNU Emacs provides the following spelling options:

(0) hate (1) HT (2) ht (3) GTE (4) the (5) He (6) Te (7) he (8) Hts
(9) hie (:) hoe (;) hue (<) Rte (=) Ste (>) Ute (@) ate (B) rte

It also lists some options in the minibuffer:

C-h or ? for more options; SPC to leave unchangedo Character to
replace word

On pressing the number 4, the word is replaced with the correct spelling. If the spelling is already correct, then GNU Emacs will tell you that the word is correct. You can also spell check a region using M-x ispell-region and a buffer using M-x ispell-buffer. If you would like to stop the spell checker while it is running, you can use M-x ispell-kill-ispell. There is a flyspell mode that can check your spelling as you type. You can enable it using M-x flyspell-mode. If you want this mode only in a buffer, you can use M-x flyspell-buffer.

Word abbreviation

GNU Emacs can complete words for you. If you type ‘ba’ and then hit M-/, then GNU Emacs will try to complete the word for you. If you continue to use ‘M-/’, it will cycle through the various options such as ‘backwards’, ‘ball’, ‘bash’, ‘bar’, ‘back’, ‘based’ etc. To enter into the abbreviation mode, you need to use M-x abbrev-mode followed by the Enter key.

The abbreviations can either be local or global. Suppose, you want to define a local abbreviation for ‘international’, you can type in ‘intl’ and use C-x a i l to define the expansion. It will prompt you with the message ‘Mode expansion for “intl”:’. You can then type the word ‘international’. The next time you enter ‘intl’ followed by the space key, GNU Emacs will automatically expand the same for you. In order to define a global expansion, you need to use C-x a i g command sequence. If you would like to remove all abbreviations for the current session, you can use M-x kill-all-abbrevs followed by the Enter key.

You can save the abbreviations to a file, say ~/.emacs.d/.abbrev_defs, using M-x write-abbrev-file for future use. You can also edit the stored abbreviations using M-x edit-abbrevs shortcut. If you would like to view all the defined abbreviations, you can use M-x list-abbrevs. The relevant contents of ~/.emacs.d/.abbrev_defs are shown below:

;;-*-coding: utf-8;-*-
(define-abbrev-table 'Buffer-menu-mode-abbrev-table '())

(define-abbrev-table 'completion-list-mode-abbrev-table '())

(define-abbrev-table 'edit-abbrevs-mode-abbrev-table '())

(define-abbrev-table 'emacs-lisp-mode-abbrev-table
  '(
    ("intl" "international" nil 2)
   ))

(define-abbrev-table 'fundamental-mode-abbrev-table '())

(define-abbrev-table 'global-abbrev-table '())

(define-abbrev-table 'lisp-mode-abbrev-table '())

(define-abbrev-table 'sh-mode-abbrev-table '())

(define-abbrev-table 'shell-mode-abbrev-table '())

Printing

You can print the buffer contents from GNU Emacs using M-x print-buffer command. If you would like to print a selected region, you can use M-x print-region command. These will be printed with page numbers and headers. You can also print a buffer without page numbers using M-x lpr-buffer. Similarly, to print a region without page numbers, use M-x lpr-region. If you are already using the Dired mode, you can select the files that you want to print using the P shortcut, and then execute in Dired mode to print them.