6.7 vi / vim Modes, plus nano, Emacs & EDITOR Awareness (103.8)

6.7 vi / vim Editor Essentials & Modes

Quick Summary: The vi editor (and its enhanced descendant vim) is the universal, POSIX-mandated visual text editor present by default across all Linux distributions. vi is a modal editor operating in three distinct states: Command (Normal) Mode for navigation, copying, and deletion; Insert Mode for entering text; and Ex (Command-Line) Mode (prefixed with :) for file I/O, search, configuration, and regular expression substitution (:%s/find/replace/g).

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1. The Three Operational Modes of vi

Unlike conventional modeless text editors (such as nano), keystrokes in vi perform radically different operations depending on the currently active mode:

vi Modal State Transitions:
                     ┌──────────────────────────────┐
                     │  Command Mode (Normal Mode)  │
                     │  (Default mode upon launch)  │
                     └───────┬──────────────▲───────┘
         Insert Keys:        │              │  Exit Insert Mode:
    `i`, `I`, `a`, `A`,      │              │  `<Esc>` key
    `o`, `O`, `s`, `S`, `C`  ▼              │
                     ┌──────────────────────────────┐
                     │         Insert Mode          │
                     │  (Typing / Editing buffer)   │
                     └──────────────────────────────┘
                             ▲              │
        Command completes    │              │  Enter Ex Mode:
        or `<Esc>` pressed   │              │  `:` (Colon), `/`, `?`
                     ┌───────┴──────────────▼───────┐
                     │     Ex Mode (Command-Line)   │
                     │  (`:w`, `:q!`, `:%s///g`)    │
                     └──────────────────────────────┘

Mode Definitions

1. Command Mode (Normal Mode): The default landing mode when opening any file (vi filename). Keystrokes are interpreted as navigation, text manipulation, deletion, yanking (copying), or mode-switching commands.
2. Insert Mode: Active text entry mode where typed characters are inserted directly into the text buffer. Indicated by -- INSERT -- at the bottom left in vim.
3. Ex Mode (Command-Line Mode): Invoked from Command Mode by typing a colon (:), forward slash (/), or question mark (?). Displays a command line prompt at the bottom of the screen to execute file operations, search patterns, buffer writes, or environment configuration.

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2. Entering Insert Mode from Command Mode

Transitioning from Command Mode to Insert Mode is accomplished using specific single-letter keystrokes that simultaneously set the cursor position:

Exam Rule: To return to Command Mode from Insert Mode or Ex Mode, press the <Esc> key.

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3. Navigation in Command Mode

Efficient navigation in vi eliminates the need for arrow keys or mouse movement:

Directional & Character Navigation

• h: Move cursor one character to the left.
• j: Move cursor one line down.
• k: Move cursor one line up.
• l: Move cursor one character to the right.

In-Line Positioning

• 0 (Zero): Jump to the absolute beginning of the current line (column 0).
• ^: Jump to the first non-blank (whitespace) character on the current line.
• $: Jump to the end of the current line.

Word-Level Navigation

• w: Jump forward to the start of the next word.
• W: Jump forward to the start of the next space-delimited WORD.
• b: Jump backward to the start of the previous word.
• B: Jump backward to the start of the previous space-delimited WORD.
• e: Jump forward to the end of the current or next word.

File-Wide Jumps & Screen Paging

• G: Jump to the last line of the file.
• 1G or gg: Jump to the first line of the file.
• <N>G (e.g., 45G): Jump directly to line number <N>.
• Ctrl+F: Scroll forward one full screen page.
• Ctrl+B: Scroll backward one full screen page.
• Ctrl+D: Scroll down half a screen page.
• Ctrl+U: Scroll up half a screen page.
• H / M / L: Jump to High (top), Middle, or Low (bottom) line of current screen display.

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4. Text Manipulation: Delete, Yank, Paste & Undo

In vi, deletion operations double as "cut" operations, placing deleted content into the default yank buffer.

Deletion Operators (Command Mode)

Yanking (Copying) and Pasting

• yy (or Y): Yank (copy) the entire current line into the buffer.
• <N>yy (e.g., 3yy): Yank <N> lines starting from current line.
• yw: Yank word from cursor.
• y$: Yank from cursor to the end of the line.
• p (lowercase): Paste buffer contents below the current line (or after cursor).
• P (uppercase): Paste buffer contents above the current line (or before cursor).

Undo, Redo, and Repeat

• u: Undo the most recent modification.
• Ctrl+R: Redo the previously undone change (vim).
• U: Undo all modifications made on the current line.
• . (Period): Repeat the last text-modifying editing command.
• r<char>: Replace character under cursor with <char> without entering insert mode.
• R: Enter Replace mode (overwrites text continuously until <Esc> is pressed).
• J: Join the current line with the line immediately below it.

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5. Ex Mode (:): File Management, Configuration & Search/Replace

Typing : in Command Mode places the cursor on the bottom status line to execute Ex commands.

Saving, Quitting & Exiting

Editor Environment Settings (:set)

:set number      # (or :set nu) Display line numbers
:set nonumber    # (or :set nonu) Hide line numbers
:set ignorecase  # (or :set ic) Case-insensitive pattern searching
:set noignorecase# (or :set noic) Case-sensitive pattern searching
:set hlsearch    # Highlight all search pattern matches
:set nohlsearch  # Disable search highlighting
:set autoindent  # Enable automatic indentation on new lines
:set all         # Display list of all editor settings

Pattern Searching

• /pattern: Search forward through buffer for pattern.
• ?pattern: Search backward through buffer for pattern.
• n: Repeat search for next match in the same direction.
• N: Repeat search for next match in the opposite direction.

Global Search and Replace (Substitution)

The Ex substitution command utilizes the general syntax:

$:[\text{range}]\text{s}/\text{pattern}/\text{replacement}/[\text{flags}]$

# 1. Replace first occurrence of 'http' with 'https' on the current line:
:s/http/https/

# 2. Replace ALL occurrences of 'http' with 'https' on the current line:
:s/http/https/g

# 3. Replace all occurrences across lines 10 through 50:
:10,50s/old_param/new_param/g

# 4. Replace ALL occurrences across the ENTIRE file (% represents 1,$):
:%s/eth0/ens33/g

# 5. Replace across entire file with interactive confirmation prompt for each match:
:%s/debug=false/debug=true/gc

# 6. Using alternative delimiter (#) to avoid escaping directory slashes:
:%s#/var/log#/opt/logs#g

💡 LPIC-1 Exam Fill-in-the-Blank Alert: What single command-mode keystroke in vi undoes the most recent change? Answer: u

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6. The Other Editors LPI Expects You to Recognise

Objective 103.8 requires you to navigate and edit in vi, but its Key Knowledge Areas also demand awareness of Emacs, nano and vim, plus the ability to configure the standard editor. You will not be asked to edit a file in Emacs — you will be asked to identify it, or to name the variable that selects a default editor.

Configuring the Standard Editor

Many programs — crontab -e, visudo, git commit, systemctl edit, less -v — need to launch "the user's editor." They resolve it from environment variables, checking VISUAL first and falling back to EDITOR:

# Set for the current shell only
$ export EDITOR=/usr/bin/vim
$ export VISUAL=/usr/bin/vim

# Make it permanent for one user
$ echo 'export EDITOR=/usr/bin/vim' >> ~/.bashrc

# Make it permanent system-wide
# echo 'export EDITOR=/usr/bin/nano' > /etc/profile.d/editor.sh

# Override for a single invocation
$ EDITOR=nano crontab -e

Debian and Ubuntu add a distribution-specific layer on top: the /usr/bin/editor symlink, managed by the alternatives system.

# Interactively choose the system-wide default editor on Debian/Ubuntu
# update-alternatives --config editor

# Show which binary /usr/bin/editor currently points at
$ readlink -f /usr/bin/editor
/usr/bin/vim.basic

Exam Rule: VISUAL takes precedence over EDITOR when both are set. VISUAL historically meant "a full-screen editor is usable on this terminal" while EDITOR meant "line editor safe on any terminal"; in practice both are set to the same value. If neither variable is set, most tools fall back to a compiled-in default — commonly vi on Red Hat family systems and nano on Debian family systems.

Exam Rule: If a question describes an editor whose commands are Ctrl+O to save and Ctrl+X to exit with a two-line help footer, the answer is nano. If the commands are Ctrl+x Ctrl+s and Ctrl+x Ctrl+c, the answer is Emacs. If the editor has separate modes and :wq saves and quits, the answer is vi/vim.