LESS 颜色 —— 通过 LESS_TERMCAP_*、LESS=R、MANPAGER 给 man 页面着色

# The canonical 6-var set — drop into ~/.bashrc / ~/.zshrc verbatim.
# Bold red for keywords / commands (md), green underline for arguments
# (us), yellow standout for status line + search matches (so).

export LESS_TERMCAP_md=$'\e[01;31m'      # start bold        (man: keywords)
export LESS_TERMCAP_me=$'\e[0m'          # end bold / blink / standout
export LESS_TERMCAP_us=$'\e[01;32m'      # start underline   (man: args / files)
export LESS_TERMCAP_ue=$'\e[0m'          # end underline
export LESS_TERMCAP_so=$'\e[01;44;33m'   # start standout    (status / search hit)
export LESS_TERMCAP_se=$'\e[0m'          # end standout
export LESS_TERMCAP_mb=$'\e[01;31m'      # start blink — copy md so it stays visible

# Verify they are exported with the right bytes (decode the ESC):
env | grep LESS_TERMCAP | cat -v
#   should show ^[[01;31m etc — the ^[ is ESC (0x1b), the rest is the SGR

# See the effect immediately — load a man page:
man ls

# Quick a/b test — unset, reload, compare:
( unset LESS_TERMCAP_md LESS_TERMCAP_me LESS_TERMCAP_us \
        LESS_TERMCAP_ue LESS_TERMCAP_so LESS_TERMCAP_se; \
  man ls )
# vs the current shell session with the vars set.

# Note the $'...' syntax — bash / zsh ANSI-C quoting that turns \e into
# the literal ESC byte. If your shell does NOT support $'...' (older sh /
# dash) use printf:
#   LESS_TERMCAP_md=$(printf '\e[01;31m'); export LESS_TERMCAP_md

# Set the default once — every less invocation gains -R:
export LESS=R

# Optional companion flags many users add to LESS:
export LESS='-R -F -X'
#   -R   keep SGR bytes (already covered above)
#   -F   quit if output fits one screen (skip the pager-trap on short files)
#   -X   skip the alt-screen restore (so scrollback retains the pager content)

# These are the same flags git auto-sets when invoking its DEFAULT pager.
# Custom pagers (core.pager, PAGER, MANPAGER) do NOT inherit them — set
# LESS globally instead.

# One-shot — no env, flags on the command line:
git log --color=always --oneline | less -R
grep --color=always -rn TODO src/    | less -R
ls --color=always -la                 | less -R

# Without -R (the default), you see literal noise:
ls --color=always | less
#   src/  app/  ESC[01;34mlib^[[0mESC[m  ...  (ugly)

# With -R, colour passes through:
ls --color=always | less -R
#   src/  app/  (bold blue lib)  ...        (correct)

# Verify LESS is honoured by the binary:
echo "$LESS"
less --help 2>&1 | grep -E 'RAW|environment' | head

# Set both — covers groff-SGR path AND backspace-overstrike path:
export MANPAGER='less -R'
export MANROFFOPT='-c'              # tell groff to emit SGR (modern groff)

# Plus the LESS_TERMCAP_* vars from snippet 1 (for the overstrike path).

# Check which path your distro uses — run man on any page, then in less
# press 'v' to drop into $EDITOR (or use !cat) and look at the raw bytes:
#
#   If you see "b\bbo\bol\bld" overstrike → backspace-overstrike path,
#                                              LESS_TERMCAP_* is in play.
#   If you see "\x1b[1mbold\x1b[0m"        → groff-SGR path,
#                                              MANPAGER='less -R' is what matters.

# Force the overstrike path even on a modern distro (so LESS_TERMCAP_*
# applies again — useful when debugging custom palettes):
export GROFF_NO_SGR=1

# Test:
man ls
# Try changing LESS_TERMCAP_md to a glaring colour and reload to confirm
# which path is active:
export LESS_TERMCAP_md=$'\e[01;45m'        # purple background
man ls    # if you see purple text → overstrike path; else → SGR path

# When piping man output (e.g. into grep / a file) the formatting is
# normally stripped because the pager is not a TTY. Preserve it with:
MAN_KEEP_FORMATTING=1 man ls | head -50    # keeps overstrike bytes
# Then strip later with col -b:
MAN_KEEP_FORMATTING=1 man ls | col -b | head -50    # plain text

# Default Debian / Ubuntu setup (already in /etc/profile.d/less.sh):
export LESSOPEN="| /usr/bin/lesspipe %s"
export LESSCLOSE="/usr/bin/lesspipe %s %s"

# Verify it's working — should show metadata not raw bytes:
less /usr/lib/x86_64-linux-gnu/libc.so.6      # ELF binary → strings dump
less /etc/os-release                          # text file → straight through
less ./some.tar.gz                            # archive → tar tvfz listing

# Add syntax highlighting for source code via source-highlight:
sudo apt install source-highlight              # Debian / Ubuntu
brew install source-highlight                  # macOS

# Wire it as the pre-processor — note leading space in LESS:
export LESSOPEN="| /usr/bin/src-hilite-lesspipe.sh %s"
export LESS=" -R"                              # leading space prevents typoed
                                               # binary name issues

# Test it:
less app/page.tsx                              # should show syntax-highlighted TS
less script.sh                                 # should show syntax-highlighted bash
less /etc/nginx/nginx.conf                     # should show coloured nginx config

# Disable for one invocation (debugging):
LESSOPEN= less raw.log
less --no-lessopen raw.log                     # explicit flag, less v530+

# Combine with bat for richer highlighting (snippet 5 explores bat more):
export LESSOPEN="| /usr/bin/bat --color=always --paging=never %s"

# Install:
#   Arch:        pacman -S bat
#   Debian/Ubuntu: apt install bat   (binary is "batcat", not "bat")
#   Fedora:      dnf install bat
#   macOS:       brew install bat

# Debian / Ubuntu workaround — alias batcat back to bat:
alias bat='batcat'

# Use as a cat replacement (paging only when output exceeds terminal):
bat app/page.tsx                              # syntax-highlighted, line numbers
bat -p app/page.tsx                           # plain mode (no header, no pager)
bat -A binary.dat                             # show non-printable as escapes

# Use as MANPAGER for colourised man pages:
export MANPAGER="sh -c 'col -bx | bat -l man -p'"
#   col -bx       strip backspace-overstrike (otherwise bat sees garbage)
#   bat -l man    syntax = man (highlights options + section refs)
#   bat -p        plain mode (no header)

# Theme + style configuration:
export BAT_THEME='OneHalfDark'                # any theme from --list-themes
export BAT_STYLE='numbers,changes,header'     # opt-in column set
export BAT_PAGER='less -R'                    # override default pager

# Verify which binary, where the config file lives:
bat --version
bat --config-file                              # path; create + edit to persist
bat --generate-config-file                     # write a fully-commented template

# Pipe coloured input into bat (preserve SGR):
git log --color=always --oneline | bat --paging=always
diff -u old.txt new.txt | bat -l diff

# Use as drop-in cat (with caveats — bat exits with paging on long output):
alias cat='bat -p'                             # plain mode = no extra UI

# Install:
#   diff-so-fancy: brew install diff-so-fancy   (or npm i -g diff-so-fancy)
#   delta:         brew install git-delta       (or cargo install git-delta)

# diff-so-fancy — wire into git core.pager:
git config --global core.pager 'diff-so-fancy | less --tabs=4 -RFX'
git config --global interactive.diffFilter 'diff-so-fancy --patch'

# Optional colour tuning that diff-so-fancy assumes:
git config --global color.diff-highlight.oldNormal    'red bold'
git config --global color.diff-highlight.oldHighlight 'red bold 52'
git config --global color.diff-highlight.newNormal    'green bold'
git config --global color.diff-highlight.newHighlight 'green bold 22'
git config --global color.diff.meta       'yellow'
git config --global color.diff.frag       'magenta bold'
git config --global color.diff.commit     'yellow bold'
git config --global color.diff.old        'red bold'
git config --global color.diff.new        'green bold'
git config --global color.diff.whitespace 'red reverse'

# delta — wire it as the pager (auto-detects):
git config --global core.pager delta
git config --global interactive.diffFilter 'delta --color-only'
git config --global delta.navigate true
git config --global delta.light false
git config --global delta.line-numbers true
git config --global delta.side-by-side true
git config --global delta.syntax-theme 'OneHalfDark'

# Disable for one command:
git --no-pager diff
git -c core.pager=cat diff

# Test:
git diff HEAD~1
git log --oneline -p | head -50

# Pipe a raw diff (not via git) into either tool:
diff -u old.txt new.txt | diff-so-fancy | less -R
diff -u old.txt new.txt | delta

# ~/.bashrc (Linux) or ~/.bash_profile (macOS Terminal.app):
export LESS_TERMCAP_md=$'\e[01;31m'     # bold        → bold red
export LESS_TERMCAP_me=$'\e[0m'
export LESS_TERMCAP_us=$'\e[01;32m'     # underline   → bold green
export LESS_TERMCAP_ue=$'\e[0m'
export LESS_TERMCAP_so=$'\e[01;44;33m'  # standout    → bold yellow-on-blue
export LESS_TERMCAP_se=$'\e[0m'
export LESS_TERMCAP_mb=$'\e[01;31m'
export LESS='-R -F -X'
export MANPAGER='less -R'
export MANROFFOPT='-c'
export PAGER='less'

# ~/.zshrc / ~/.zprofile (same syntax, $'...' works in zsh too):
export LESS_TERMCAP_md=$'\e[01;31m'
# ... (same six exports)
export LESS='-R -F -X'
export MANPAGER='less -R'

# ~/.config/fish/config.fish — fish has NO $'...' quoting, use printf:
set -gx LESS_TERMCAP_md (printf '\e[01;31m')
set -gx LESS_TERMCAP_me (printf '\e[0m')
set -gx LESS_TERMCAP_us (printf '\e[01;32m')
set -gx LESS_TERMCAP_ue (printf '\e[0m')
set -gx LESS_TERMCAP_so (printf '\e[01;44;33m')
set -gx LESS_TERMCAP_se (printf '\e[0m')
set -gx LESS_TERMCAP_mb (printf '\e[01;31m')
set -gx LESS '-R -F -X'
set -gx MANPAGER 'less -R'

# ~/.cshrc / ~/.tcshrc — printf inside backticks, setenv (no = sign):
setenv LESS_TERMCAP_md "`printf '\e[01;31m'`"
setenv LESS_TERMCAP_me "`printf '\e[0m'`"
# ... (same six setenv)
setenv LESS '-R -F -X'
setenv MANPAGER 'less -R'

# Verify:
man ls          # should show coloured keywords + underlined args
echo "$LESS"    # should print "-R -F -X"
env | grep -E 'LESS_TERMCAP|MANPAGER' | cat -v   # show with ^[ visible

# macOS double-trap reminder — these only run on LOGIN shell:
#   ~/.bash_profile, ~/.zprofile, ~/.profile
# These only run on NON-login (subshell) shell:
#   ~/.bashrc, ~/.zshrc