Command line
Note
If you don't plan to use ktlint's command line interface then you can skip this section.
Download and verification¶
Download manually from github¶
All releases of ktlint can be downloaded from the releases page.
Download using curl¶
A particular version of ktlint can be downloaded with next command which also changes the file to an executable in directory /usr/local/bin:
curl -sSLO https://github.com/pinterest/ktlint/releases/download/0.48.0/ktlint && chmod a+x ktlint && sudo mv ktlint /usr/local/bin/
Curl not installed or behind proxy
If you don't have curl installed - replace curl -sL with wget -qO-.
If you are behind a proxy see - curl / wget manpage. Usually simple:
Verification of download¶
ktlint.asc contains PGP signature which you can verify with:
curl -sS https://keybase.io/ktlint/pgp_keys.asc | gpg --import && gpg --verify ktlint.asc
curl -sS https://keybase.io/shyiko/pgp_keys.asc | gpg --import && gpg --verify ktlint.asc
Package managers¶
ktlint can be installed via several OS specific package managers.
Install with brew on macOS or Homebrew on Linux
Install with MacPorts
On Arch Linux install package ktlint AUR.
Command line usage¶
Rule set(s)¶
When no arguments are specified, the style of all Kotlin files (ending with '.kt' or '.kts') inside the current dir (recursively) are validated with the rules from the standard ruleset. Hidden folders will be skipped.
To validate with the standard ruleset and the experimental ruleset run command below:
Note
Instead of using this command line flag, you can also set .editorconfig property ktlint_experimental = enabled.
To validate with a custom ruleset run command below:
ktlint --ruleset=/path/to/custom-ruleset.jar
# or
ktlint -R /path/to/custom-ruleset.jar
Format (autocorrect)¶
Most style violations can be corrected automatically. Errors that can not be corrected, are printed to stderr.
Globs¶
Globs can be used to specify more exactly what files and directories are to be validated. ktlint uses the .gitignore pattern style syntax for globs. Globs are processed from left to right. Prepend a glob with ! to negate it. Hidden folders will be skipped.
# Check all '.kt' files in 'src/' directory, but ignore files ending with 'Test.kt':
ktlint "src/**/*.kt" "!src/**/*Test.kt"
# Check all '.kt' files in 'src/' directory, but ignore 'generated' directory and its subdirectories:
ktlint "src/**/*.kt" "!src/**/generated/**"
Violation reporting¶
ktlint supports different type of reporters for lint violations. When not specified the plain reporter is used. Optionally the plain reporter can group the violations per file.
When using ktlint on an existing project, the number of violations can be huge. To get more insights in which rules are causing the most violations, the plain-summary reporter can be used.
Other built-in reporters are: json, sarif, checkstyle, and html
Style violations can be written to an output file which is convenient when multiple reporters are specified. In example below, the plain reporter is used to write to the console while the checkstyle reports is written to a file:
ktlint --reporter=plain --reporter=checkstyle,output=ktlint-report-in-checkstyle-format.xml
If resolving all existing errors in a project is unwanted, it is possible to create a baseline and in following invocations compare violations against this baseline. Violations that are registered in the baseline, will be ignored silently. Remove the baseline file in case you want to reset it.
ktlint --baseline=ktlint-baseline.xml # Baseline is created when not existing
Logging¶
Logging information is written to stdout. The amount of logging can be influenced by setting the minimal log level using option --log-level or -l to one of values trace, debug, info, warn, error, or none to suppress all logging.
By default, the info log level is used meaning that all log lines at level info, warn and error are shown while suppressing log lines at level debug or trace.
Rule configuration (.editorconfig)¶
Some rules can be tweaked via the editorconfig file.
A scaffold of the .editorconfig file can be generated with command below. Note: that the generated file only contains configuration settings which are actively used by the rules which are loaded:
ktlint generateEditorConfig
# or
ktlint --experimental generateEditorConfig
# or
ktlint --experimental --ruleset=/path/to/custom-ruleset.jar generateEditorConfig
Normally this file is located in the root of your project directory. In case the file is located in a sub folder of the project, the settings of that file only applies to that subdirectory and its folders (recursively). Ktlint automatically detects and reads all .editorconfig files in your project.
Use command below, to specify a default editorconfig. In case a property is not defined in any .editorconfig file on the path to the file, the value from the default file is used. The path may point to any valid file or directory. The path can be relative or absolute. Depending on your OS, the "~" at the beginning of a path is replaced by the user home directory.
!!! warning "Overrides '.editorconfig' in project directory" in KtLint 0.46 and older
When specifying this option using ktlint 0.46 or older, all .editorconfig files in the project directory are being ignored. Starting from KtLint 0.47 the properties in this file are used as fallback.
Stdin && stdout¶
With command below, the input is read from stdin and the violations are printed to stderr. Logging is written to stdout.
When combined with the --format option, the formatted code is written to stdout and the violations are printed to stderr:
Tip
Logging output printed to stdout can be suppressed by setting --log-level=none (see logging).
Output printed to stderr can be suppressed in different ways. To ignore all error output, add 2> /dev/null to the end of the command line. Otherwise, specify a reporter to write the error output to a file.
Git hooks¶
Predefined git hooks can be installed, to automatically validate lint errors before commit or push.
Miscellaneous flags and commands¶
-a or --android: Turn on Android Kotlin Style Guide compatibility. This flag is most likely to be removed in a future version. Use .editorconfig ktlint_code_style.
--color and --color-name=<colorName>: Make output colorful and optionally set the color name to use.
--disabled_rules=<disabledRules>: A comma-separated list of rules to globally disable. To disable the standard ktlint rule-set use --disabled_rules=standard. This flag is most likely to be removed in a future version. Use .editorconfig disabled_rules.
-h or --help: Prints help information.
--limit=<limit>: Maximum number of errors to show (default: show all)
printAST or --print-ast: Prints AST (useful when writing/debugging rules)
--relative: Print files relative to the working directory (e.g. dir/file.kt instead of /home/user/project/dir/file.kt)
--patterns-from-stdin[=<delimiter>]: Reads additional patterns from stdin, where the patterns are separated by <delimiter>. If =<delimiter> is omitted, newline is used as fallback delimiter. If an empty string is given, the NUL byte is used as delimiter instead.
Options --stdin and --patterns-from-stdin are mutually exclusive, only one of them can be given at a time.
-V or --version: Prints version information and exit.
Microsoft Windows users¶
Microsoft Windows
On Microsoft Windows you'll have to use java -jar ktlint ....