Shfmt Configuration

shfmt Configuration

Master shfmt configuration for consistent shell script formatting across projects, including configuration files, EditorConfig integration, and team standardization.

Overview

shfmt is a shell parser, formatter, and interpreter that supports POSIX Shell, Bash, and mksh. Configuration allows you to define consistent formatting rules for your shell scripts.

Configuration Methods

shfmt supports multiple configuration approaches, in order of precedence:

1. Command-line flags (highest precedence)
2. EditorConfig settings
3. .shfmt.toml or shfmt.toml file

TOML Configuration File

Basic Configuration

Create .shfmt.toml or shfmt.toml in your project root:

# Shell dialect (posix, bash, mksh, bats)
shell = "bash"

# Indent with spaces (0 for tabs)
indent = 2

# Binary operators at start of line
binary-next-line = true

# Switch cases indented
switch-case-indent = true

# Redirect operators followed by space
space-redirects = false

# Keep column alignment paddings
keep-padding = false

# Function opening brace on next line
func-next-line = false

Configuration Options Explained

shell

Specifies the shell dialect for parsing:

# POSIX-compliant shell (most portable)
shell = "posix"

# Bash (default for .bash files)
shell = "bash"

# MirBSD Korn Shell
shell = "mksh"

# Bats (Bash Automated Testing System)
shell = "bats"

Auto-detection based on shebang if not specified:

• #!/bin/sh -> posix
• #!/bin/bash or #!/usr/bin/env bash -> bash
• #!/bin/mksh -> mksh

indent

Controls indentation style:

# 2 spaces (common)
indent = 2

# 4 spaces
indent = 4

# Tabs (use 0)
indent = 0

binary-next-line

Controls binary operator positioning:

# Operators at end of line (default)
binary-next-line = false

# Result:
if [ "$a" = "foo" ] &&
   [ "$b" = "bar" ]; then
    echo "match"
fi

# Operators at start of next line
binary-next-line = true

# Result:
if [ "$a" = "foo" ] \
    && [ "$b" = "bar" ]; then
    echo "match"
fi

switch-case-indent

Controls case statement indentation:

# Cases at same level as switch (default)
switch-case-indent = false

# Result:
case "$1" in
start)
    do_start
    ;;
stop)
    do_stop
    ;;
esac

# Cases indented inside switch
switch-case-indent = true

# Result:
case "$1" in
    start)
        do_start
        ;;
    stop)
        do_stop
        ;;
esac

space-redirects

Controls spacing around redirections:

# No space before redirect (default)
space-redirects = false

# Result:
echo "hello" >file.txt
cat <input.txt

# Space before redirect
space-redirects = true

# Result:
echo "hello" > file.txt
cat < input.txt

keep-padding

Preserves alignment padding:

# Remove extra alignment spaces (default)
keep-padding = false

# Input with alignment:
short="value"
longer_var="another"

# Result (alignment removed):
short="value"
longer_var="another"

# Preserve alignment
keep-padding = true

# Result (alignment kept):
short=     "value"
longer_var="another"

func-next-line

Controls function brace placement:

# Opening brace on same line (default)
func-next-line = false

# Result:
my_function() {
    echo "hello"
}

# Opening brace on next line
func-next-line = true

# Result:
my_function()
{
    echo "hello"
}

EditorConfig Integration

shfmt respects EditorConfig settings. Create or update .editorconfig:

# EditorConfig is awesome: https://EditorConfig.org

root = true

[*]
indent_style = space
indent_size = 2
end_of_line = lf
charset = utf-8
trim_trailing_whitespace = true
insert_final_newline = true

[*.sh]
indent_style = space
indent_size = 2

# shfmt-specific options
shell_variant = bash
binary_next_line = true
switch_case_indent = true
space_redirects = false
keep_padding = false
function_next_line = false

EditorConfig Option Mapping

Command-Line Flags

Basic Usage

# Format file in place
shfmt -w script.sh

# Show diff of changes
shfmt -d script.sh

# List files that need formatting
shfmt -l .

# Format and output to stdout
shfmt script.sh

Formatting Options

# Set indent to 4 spaces
shfmt -i 4 script.sh

# Use tabs for indentation
shfmt -i 0 script.sh

# Specify shell dialect
shfmt -ln bash script.sh

# Binary operators on next line
shfmt -bn script.sh

# Indent switch cases
shfmt -ci script.sh

# Space after redirects
shfmt -sr script.sh

# Preserve padding
shfmt -kp script.sh

# Function brace on next line
shfmt -fn script.sh

Combined Example

# Common configuration
shfmt -i 2 -ci -bn -w script.sh

Project Configuration Patterns

Minimal Bash Project

# .shfmt.toml
shell = "bash"
indent = 2

POSIX-Compliant Scripts

# .shfmt.toml
shell = "posix"
indent = 4
binary-next-line = false
switch-case-indent = false

Modern Bash with All Features

# .shfmt.toml
shell = "bash"
indent = 2
binary-next-line = true
switch-case-indent = true
space-redirects = false
func-next-line = false

Team Standardization

# .shfmt.toml - enforce team standards
shell = "bash"
indent = 2
binary-next-line = true
switch-case-indent = true
keep-padding = false

CI/CD Integration

GitHub Actions

name: Shell Format Check
user-invocable: false
on: [push, pull_request]
jobs:
  shfmt:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Install shfmt
        run: |
          curl -sS https://webinstall.dev/shfmt | bash
          export PATH="$HOME/.local/bin:$PATH"
      - name: Check formatting
        run: shfmt -d .

Pre-commit Hook

# .pre-commit-config.yaml
repos:
  - repo: https://github.com/scop/pre-commit-shfmt
    rev: v3.8.0-1
    hooks:
      - id: shfmt
        args: ["-w"]

Makefile Target

.PHONY: fmt-check fmt

fmt-check:
 shfmt -d .

fmt:
 shfmt -w .

Best Practices

1. Commit Configuration - Always commit .shfmt.toml for team consistency
2. Match Dialect - Set shell to match your script shebangs
3. EditorConfig First - Use EditorConfig for IDE integration
4. CI Enforcement - Run shfmt -d in CI to catch formatting issues
5. Consistent Indentation - Pick 2 or 4 spaces and stick with it
6. Document Choices - Add comments explaining non-default options
7. Version Lock - Pin shfmt version in CI for reproducibility

Troubleshooting

Configuration Not Applied

Check precedence order:

1. Command-line flags override everything
2. EditorConfig in file's directory
3. .shfmt.toml in project root

Wrong Shell Dialect

Verify shebang matches configuration:

# If using shell = "bash", ensure scripts have:
#!/usr/bin/env bash
# or
#!/bin/bash

EditorConfig Not Detected

Ensure EditorConfig file is in parent directory chain and has correct section:

[*.sh]
shell_variant = bash

When to Use This Skill

• Setting up shfmt in new projects
• Configuring team-wide formatting standards
• Integrating shfmt with CI/CD pipelines
• Troubleshooting configuration issues
• Migrating between configuration methods
• Setting up EditorConfig for shell scripts