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⚙️ Feature-rich syntax highlighting


Install F-Sy-H

Add the following to your .zshrc file.

zi light z-shell/F-Sy-H

Load the plugin in turbo mode:

zi wait lucid for \
atinit"ZI[COMPINIT_OPTS]=-C; zicompinit; zicdreplay" \
z-shell/F-Sy-H \
blockf \
zsh-users/zsh-completions \
atload"!_zsh_autosuggest_start" \


Performance differences can be observed in this Asciinema recording, where a 10 kB function is being edited.

Syntax highlighting features


Switch themes via fast-theme {theme-name}.

Run fast-theme -t {theme-name} option to obtain the snippet above.

Run fast-theme -l to list available themes.

Theme guide for F-Sy-H

To select a theme using fast-theme. F-Sy-H currently has 11 themes basic INI files where each key is a style, they can be listed with fast-theme -l.

Besides shipped themes, users can point this tool to any other theme, by simple fast-theme ~/mytheme.ini. To obtain a template to work on when creating your theme, issue fast-theme --copy-shipped-theme {theme-name}.

To alter just a few styles and not create a whole new theme, use overlay. What is an overlay? It is in the same format as a full theme but can have only a few styles defined, and these styles will overwrite styles in the main theme.

Example overlay file:

; overlay.ini
commandseparator = yellow,bold
comment = 17

function = green
command = 180

File name overlay.ini is treated specially.

When specifying a path, the following short-hands can be used:

XDG:    = ~/.config/fsh (respects $XDG_CONFIG_HOME env var)
LOCAL: = /usr/local/share/fsh/
HOME: = ~/.fsh/
OPT: = /opt/local/share/fsh/

So for example, issue fast-theme XDG:overlay to load ~/.config/fsh/overlay.ini as an overlay. The .ini extension is optional.

Secondary theme

Each theme has a key secondary, e.g. for theme free:

; free.ini
default = none
unknown-token = red,bold
; ...
; ...
; ...
secondary = zdharma

A secondary theme (zdharma in the example) will be used for highlighting of argument for eval and of $( ... ) interior (i.e. of the interior of command substitution). Recursive highlighting uses the alternate theme to make the highlighted code distinct:

In the above screen-shot the interior of $( ... ) uses different colors than the rest of the code. Example for eval:

The first line doesn't use recursive highlighting, highlights the eval argument as a regular string. The second line switches the theme to zdharma and does full recursive highlighting of the eval argument.


Comparing to the project zsh-users/zsh-syntax-highlighting (the upper image):



Comparing to the project zsh-users/zsh-syntax-highlighting (the upper line):


Exact highlighting that recognizes quoting.


exec descriptor-variables

Comparing to the project zsh-users/zsh-syntax-highlighting (the upper line):

The for-loops and alternate syntax (brace {/} blocks)

Function definitions

Comparing to the project zsh-users/zsh-syntax-highlighting (the upper 2 lines):

Recursive eval and $( ) highlighting

Comparing to the project zsh-users/zsh-syntax-highlighting (the upper line):

Chroma functions

Command specific highlighting




Git commit

Git checkout





The chromas are set in fast-highlight#L174.

Fpath highlighting

Case highlighting

Math highlighting

Zcalc highlighting

Custom Working Directory

Set $FAST_WORK_DIR before loading the plugin to have e.g. processed theme files (ready to load, in Zsh format, not INI) kept under a specified location. This is handy if e.g. you install Fast-Syntax-Highlighting system-wide (e.g. from AUR on ArchLinux) and want to have a per-user theme setup.

You can use "~" in the path, e.g. FAST_WORK_DIR=~/.fsh and also the XDG:, LOCAL:, OPT:, etc. short-hands, so e.g. FAST_WORK_DIR=XDG or FAST_WORK_DIR=XDG: is allowed (in this case it will be changed to $HOME/.config/fsh by default by F-Sy-H loader).

Chroma guide for F-Sy-H

This document explains to create a detailed highlighting for a specific program.


  • chroma - a shorthand for chroma function – the thing that colorizes selected commands, like git, grep, etc. invocations, see chroma function below,
  • big loop - main highlighting code, a loop over tokens, and at least 2 large structure constructs (big if and case); it is advanced, e.g. parses case statements, here-string, it constitutes 90% of the F-Sy-H project,
  • chroma function - a plugin function that is called when a specific command occurs (e.g. when a user enters git at the command line) suppressing activity of big loop (i.e. no standard highlighting unless requested),
  • token - the result of splitting the whole command line (i.e. $BUFFER, the Zle variable) into bits called tokens, which are words in general, separated by spaces on the command line.

Overview of functioning

  1. Big loop is working – token by token processes command line, changes states (e.g. enters state "inside case statement") and in the end decides on the color of the token currently processed.
  2. Big loop occurs a command that has a chroma, e.g. git.
  3. Big loop enters "chroma" state, calls associated chroma function.
  4. Chroma takes care of the "chroma" state, and ensures it will be set also for the next token.
  5. "chroma" state is active, so all following tokens are routed to the chroma (in general skipping big-loop, see next items),
  6. When processing of a single token is complete, the associated chroma returns 0 (shell-truth) to request no further processing by the big loop.
  7. It can also return 1 so that a single, current token will be passed into a big-loop for processing (to do a standard highlighting).

Chroma function arguments

  • $1 - 0 or 1, denoting if it's the first call to the chroma, or the following one,
  • $2 - the current token, also accessible by $\__arg from the upper scope - basically a private copy of $__arg; the token can be eg.: "grep",
  • $3 - a private copy of $_start_pos, i.e. the position of the token in the command line buffer, used to add region_highlight entry (see man) because Zsh colorizes by _ranges* applied onto command line buffer (e.g. from-10 to-13 fg=red),
  • $4 - a private copy of $_end_pos from the upper scope; denotes where the current token ends (at which index in the string is the command line).

So example invocation could look like this:

→chroma/ 1 "grep" "$_start_pos" "$_end_pos"

Big-loop will be doing such calls for the user, after occurring a specific chroma-enabled command (like e.g. awk), and then until chroma will detect the end of this chroma-enabled command (end of the whole invocation, with arguments, etc.; in other words, when e.g. new line or ;-character occurs, etc.).

Example of chroma function

# -*- mode: zsh; sh-indentation: 2; indent-tabs-mode: nil; sh-basic-offset: 2; -*-
# vim: ft=zsh sw=2 ts=2 et
# Example chroma function. It colorizes the first two arguments as `builtin' style,
# third and following arguments as `globbing' style. The first two arguments may
# be "strings", they will be passed through to normal highlighter (by returning 1).
# $1 - 0 or 1, denoting if it's the first call to the chroma or the following one
# $2 - the current token, also accessible by $__arg from the above scope -
# a private copy of $__arg; the token can be eg.: "grep"
# $3 - a private copy of $_start_pos, i.e. the position of the token in the
# command line buffer, used to add region_highlight entry (see man),
# because Zsh colorizes by *ranges* in the command line buffer
# $4 - a private copy of $_end_pos from the above scope
# Overall functioning is: when command "example" occurs, this function
# is called with $1 == 1, it ("example") is the first token ($2), then for any
# following token, this function is called with $1 == 0, until end of command
# is occurred (i.e. till enter is pressed or ";" is put into the source or the
# command line simply ends).
# Other tips are:
# - $CURSOR holds cursor position
# - $BUFFER holds the whole command line buffer
# - $LBUFFER holds command line buffer that is left from the cursor, i.e. it's a
# BUFFER substring 1 .. $CURSOR
# - $RBUFFER is the same as LBUFFER but holds part of BUFFER right to the cursor
# The function receives $BUFFER but via a sequence of tokens, which are shell words,
# e.g. "a b c" is a shell word, while a b c are 3 shell words.
# FAST_HIGHLIGHT is a friendly hash array that allows storing strings without
# creating global parameters (variables). If you need hash, just use it first
# declaring, under some distinct name like: typeset -gA CHROMA_EXPLE_DICT.
# Remember to reset the hash and others at __first_call == 1, so that you have
# a fresh state for a new command.

# Keep chroma-takeover state meaning: until; handle highlighting via chroma.
# So the below 8192 assignment takes care that the next token will be routed to chroma.
(( next_word = 2 | 8192 ))

local __first_call="$1" __wrd="$2" __start_pos="$3" __end_pos="$4"
local __style
integer __idx1 __idx2

(( __first_call )) && {
# Called for the first time - new command. FAST_HIGHLIGHT is used because it survives between calls,
# and allows to use of a single global hash only, instead of multiple global string variables.

# Set style for region_highlight entry. It is used below in
# '[[ -n "$__style" ]] ...' line, which adds highlight entry, like "10 12 fg=green", through `reply' array.
# Could check if command `example' exists and set `unknown-token'
# style instead of `command'

} || {
# Following the call, i.e. not the first one

# Check if chroma should end – test if the token is of type "starts new command", if so pass-through – chroma ends
[[ "$__arg_type" = 3 ]] && return 2

if (( in_redirection > 0 || this_word & 128 )) || [[ $__wrd == "<<<" ]]; then
return 1

if [[ "$__wrd" = -* ]]; then
# Detected option, add style for it.
[[ "$__wrd" = --* ]] && \
__style=${FAST_THEME_NAME}double-hyphen-option || __style=${FAST_THEME_NAME}single-hyphen-option
# Count non-option tokens
(( FAST_HIGHLIGHT[chroma-example-counter] += 1, __idx1 = FAST_HIGHLIGHT[chroma-example-counter] ))

# Colorize 1..2 as builtin, 3.. as glob
if (( FAST_HIGHLIGHT[chroma-example-counter] <= 2 )); then
if [[ "$__wrd" = \"* ]]; then
# Pass through, fsh main code will do the highlight!
return 1

# Add region_highlight entry (via `reply' array).
# If 1 will be added to __start_pos, this will highlight "token".
# If 1 will be subtracted from __end_pos, this will highlight "toke".
# $PREBUFFER is for specific situations when users do command \<ENTER>
# i.e. when multi-line command using backslash is entered.
# This is a commonplace of adding of such entry, but any above code can do
# it (and it does in other chromas) and skip setting __style to this way to disable this code.
[[ -n "$__style" ]] && \
(( __start=__start_pos-${#PREBUFFER}, __end=__end_pos-${#PREBUFFER}, __start >= 0 )) && \
reply+=("$__start $__end ${FAST_HIGHLIGHT_STYLES[$__style]}")

# We aren't passing through, do obligatory things ourselves.
# _start_pos=$_end_pos advances pointers in command line buffer.
# To pass through means to `return 1'.
# The highlighting of this single token is then done by F-Sy-H's
# main code and chroma doesn't have to do anything.
(( this_word = next_word ))

return 0