Compile LESS files with source maps - css

Question

How can I compile a LESS file to output a source map file (.css.map) in addition to a CSS file? Is there a way to do it on both command line (NodeJS's lessc) and on any GUI-based programs?

Answer 1

Update: New shortest answer
The docs have been updated! As new features hit LESS, sometimes the docs lag behind a bit, so if you're looking for bleeding-edge features, you're still probably better off running lessc (see longer answer) and checking what pops out of the help text.
http://lesscss.org/usage/
Short answer
You're looking for any number of the following options from the command line:
--source-map[=FILENAME] Outputs a v3 sourcemap to the filename (or output filename.map)
--source-map-rootpath=X adds this path onto the sourcemap filename and less file paths
--source-map-basepath=X Sets sourcemap base path, defaults to current working directory.
--source-map-less-inline puts the less files into the map instead of referencing them
--source-map-map-inline puts the map (and any less files) into the output css file
--source-map-url=URL the complete url and filename put in the less file
As I write this I'm not aware of any GUI options that generate maps (source maps were only added to LESS in the last few months) -- sorry to not have any better news. I'm sure they'll add support in as they update over the next year.
Longer answer
If you run lessc from the command line without any parameters it will give you all the options. (In my experience, this is more up to date than their documentation, so it'll at least get you pointed in the right direction.) with all the most recent map stuff included.
The easiest combo to use for dev is --source-map-less-inline --source-map-map-inline as that will give you your source maps embedded in your output css.
If you'd like to add a separate map file, you can use --source-map which, from my.less will output my.css and my.css.map
For reference: when I run my copy (v 1.6.1 at the moment) I get
usage: lessc [option option=parameter ...] <source> [destination]
If source is set to `-' (dash or hyphen-minus), input is read from stdin.
options:
-h, --help Print help (this message) and exit.
--include-path=PATHS Set include paths. Separated by `:'. Use `;' on Windows.
-M, --depends Output a makefile import dependency list to stdout
--no-color Disable colorized output.
--no-ie-compat Disable IE compatibility checks.
--no-js Disable JavaScript in less files
-l, --lint Syntax check only (lint).
-s, --silent Suppress output of error messages.
--strict-imports Force evaluation of imports.
--insecure Allow imports from insecure https hosts.
-v, --version Print version number and exit.
-x, --compress Compress output by removing some whitespaces.
--clean-css Compress output using clean-css
--clean-option=opt:val Pass an option to clean css, using CLI arguments from
https://github.com/GoalSmashers/clean-css e.g.
--clean-option=--selectors-merge-mode:ie8
and to switch on advanced use --clean-option=--advanced
--source-map[=FILENAME] Outputs a v3 sourcemap to the filename (or output filename.map)
--source-map-rootpath=X adds this path onto the sourcemap filename and less file paths
--source-map-basepath=X Sets sourcemap base path, defaults to current working directory.
--source-map-less-inline puts the less files into the map instead of referencing them
--source-map-map-inline puts the map (and any less files) into the output css file
--source-map-url=URL the complete url and filename put in the less file
-rp, --rootpath=URL Set rootpath for url rewriting in relative imports and urls.
Works with or without the relative-urls option.
-ru, --relative-urls re-write relative urls to the base less file.
-sm=on|off Turn on or off strict math, where in strict mode, math
--strict-math=on|off requires brackets. This option may default to on and then
be removed in the future.
-su=on|off Allow mixed units, e.g. 1px+1em or 1px*1px which have units
--strict-units=on|off that cannot be represented.
--global-var='VAR=VALUE' Defines a variable that can be referenced by the file.
--modify-var='VAR=VALUE' Modifies a variable already declared in the file.
-------------------------- Deprecated ----------------
-O0, -O1, -O2 Set the parser's optimization level. The lower
the number, the less nodes it will create in the
tree. This could matter for debugging, or if you
want to access the individual nodes in the tree.
--line-numbers=TYPE Outputs filename and line numbers.
TYPE can be either 'comments', which will output
the debug info within comments, 'mediaquery'
that will output the information within a fake
media query which is compatible with the SASS
format, and 'all' which will do both.
--verbose Be verbose.

Answer 2

If the command line doesn't suite you, Grunt is great at this type of thing. You can configure the grunt-contrib-less plugin to generate inline maps with a config like this:
less: {
options: {
sourceMap:true,
outputSourceFiles: true
},
lessFiles: {
expand: true,
flatten:false,
src: ['**/*.less'],
dest: ['dist/'],
ext: '.css',
}
},
https://github.com/gruntjs/grunt-contrib-less

Answer 3

Example to Create Map and CSS file from Less File
Install latest Node JS and go to command prompt and run npm install less, Now less installed successfully
Go to Command Prompt and move to less file folder that we are going to create
For e.g., I am going to change HelloWorld [Less File]
In Command prompt go to C:\Project\CSS or give the correct path in the below command.
Run following Command in Command Prompt
lessc HelloWorld.less HelloWorld.css --source-map=HelloWorld.css.map –verbose
Now CSS and Map file is generated in the respective folder.
For more reference check the link : royalarun.blogspot.com