Day 2 - vi Search and Replace, and Other Editors

📌 Key Points

• Search with /pattern (downward) and ?pattern (upward); the next result is n and the opposite direction is N.
• The basic form of substitution is :s/find/replace/.
• % means the whole file, and g means everything within a line. :%s/A/B/g is the classic form.
• vi settings are stored in ~/.vimrc (personal) and /etc/vimrc (global).
• nano shows its shortcut keys at the bottom of the screen, and emacs has no modes. Only vi has modes.

Search

   /error        search downward for error
   ?error        search upward for error
   n             next result
   N             next result in the opposite direction

• A search starts in command mode. When you press /, an input line appears at the bottom of the screen.
• The relationship between n and N is an exam point. N is not "upward"; it is the opposite of the direction you first searched. If you searched with ?, N goes downward.

Symbols Used in Patterns

• Since / itself is the "start search" symbol, if the string you are looking for contains a slash, put a backslash in front.
• The search does not stop at the end. It wraps around to the beginning and keeps looking, and the bottom line shows search hit BOTTOM, continuing at TOP.
• If nothing is found, E486: Pattern not found: pattern appears.
• To ignore case, use :set ic, and to temporarily turn off search highlighting use :noh (vim).

Substitution

   :  %  s / Seoul / Busan / g
   │  │  │    │        │     │
   │  │  │    │        │     └── g  everything on the line
   │  │  │    │        └──────── replacement string
   │  │  │    └───────────────── string to find
   │  │  └────────────────────── s  substitute
   │  └───────────────────────── %  the whole file
   └──────────────────────────── :  ex mode

Tell % and g apart. % decides up to which lines, and g decides how many within one line. :%s/A/B/g, with both attached, means "replace everything in the whole file."

Before and After Replacing

This is the result of using each of four commands on the same two lines, with the cursor on line 1.

   Original        1  banana apple          2  grape banana
 
   :s/a/A/         1  bAnana apple          2  grape banana      only the first on the current line
   :s/a/A/g        1  bAnAnA Apple          2  grape banana      all on the current line
   :%s/a/A/        1  bAnana apple          2  grApe banana      only the first on every line
   :%s/a/A/g       1  bAnAnA Apple          2  grApe bAnAnA      all on every line

• The third row is the trap. With only %, just "one per line" is changed. The banana on line 2 stayed as it was.

How to Write a Range

• In a range, . is the current line and $ is the last line. % is shorthand for 1,$.
• Ranges are used not only for substitution but for other ex commands too — :1,5d deletes lines 1 through 5.

Commonly Used Substitution Forms

• The delimiter does not have to be /. The character right after s becomes the delimiter.
• If you add c, it asks replace with B (y/n/a/q/l/^E/^Y)? at each match. y replace, n skip, a all the rest, q stop.
• If you replaced wrongly, undo it in command mode with u. One whole substitution is undone at once.
• The g at the end (an option) and the :g at the start (a command) are different things. The option g means "everything in a line," and the command :g means "run the following command on every line that has the pattern."

Commonly Used Settings

• To turn one off, put no in front — nonu, noai, noic, nolist. It is not that each option has its own separate off command.

• Options that take a value are given with = — ts=4. The form differs from on/off options.

• If you want to know the current value, add a question mark. :set ts? answers like tabstop=8 (the default is 8).

• Settings given this way disappear when you close the editor.

• To keep using them, write them in a configuration file.

   " ~/.vimrc example
   set nu
   set ai
   set ts=4

• It is the same structure as the shell's .bashrc. If it starts with ~/ it is personal; if /etc/ it is global.
• Inside a configuration file, it is usual to write set nu without a colon. Comments start with a double quote ("), unlike the shell's #.
• The global file is read first and then overridden by the personal file. The location of the global file varies by distribution: /etc/vimrc on the Red Hat family and /etc/vim/vimrc on the Debian family.

Other Editors

nano

   ^G Get Help    ^O Write Out    ^X Exit
   └ ^ means the Ctrl key

• There are no modes. When you open it, you can start typing right away.
• A list of shortcuts is always visible at the bottom of the screen. That is why it is easy for beginners.
• It is an improved version of pico and was made by the GNU project.

   Ctrl+X
   Save modified buffer?   Y Yes   N No   ^C Cancel     ← Y
   File Name to Write: memo.txt                         ← Enter

• If you press Ctrl+X after editing, it asks whether to save. After Y, you confirm the file name and press Enter, and it saves and exits. It does not hold out with just a warning, as vi does.
• In the list at the bottom of the screen, ^ is the Ctrl key and M- is the Alt (Meta) key.
• pico was originally an editor bundled with the mail program Pine. nano is its remake as free software.

emacs

• It was created by Richard Stallman. It is the editor of the GNU project.
• It has no modes; instead it invokes every feature with Ctrl and Meta (Alt) key combinations.
• Its features can be extended in Lisp, so it is called an environment that goes beyond an editor.

• Ctrl+X Ctrl+S means holding Ctrl while pressing x, then s. The emacs documentation writes this as C-x C-s. C- is Ctrl and M- is Meta (Alt).
• Both saving and exiting start with Ctrl+X and differ only in the following letter — with Ctrl+S it is save, with Ctrl+C it is exit.
• The meaning of yank is the opposite of vi. vi's yy is copy, while emacs's Ctrl+Y is paste.
• The Ctrl+A, Ctrl+E, Ctrl+K, and Ctrl+R on the bash command line are exactly emacs-style shortcuts. The keys we used last week come from here.
• emacs runs on the console and also in a graphical window under X Window.

Comparing the Three Editors

The answer to "Which editor has modes?" is vi. emacs and nano have no modes.

The Same Task in Three Editors

• If the shortcut is a Ctrl combination it is emacs or nano; if it is a colon or a single letter it is vi. When they are mixed in the choices, split them by this criterion first.
• If it ends with a single Ctrl+X it is nano; if it takes Ctrl+X Ctrl+C twice it is emacs. The exit keys are similar, so questions swap them.
• Ctrl+K is cut in both editors, but pasting differs: Ctrl+Y in emacs and Ctrl+U in nano.

Tomorrow we cover running programs: the concept and types of processes.

📖 Glossary

• /pattern : The vi command that searches for a string downward from the cursor.
• n / N : Keys that move through search results in the same direction / the opposite direction.
• Substitute : The ex command that replaces strings in the form :s/A/B/.
• % : A range symbol that makes the whole file the target of a substitution.
• g : An option that makes a substitution replace every match within a line.
• ~/.vimrc : vim's personal configuration file. The global configuration is /etc/vimrc.
• nano : A GNU editor that improves on pico. It has no modes and shows shortcuts at the bottom of the screen.
• emacs : A highly extensible editor created by Richard Stallman. It is operated with key combinations rather than modes.