Simply put, the
-w argument doesn't exist.
$ lessc --help
usage: lessc [option option=parameter ...] <source> [destination]
If source is set to `-' (dash or hyphen-minus), input is read from stdin.
-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.
-l, --lint Syntax check only (lint).
-s, --silent Suppress output of error messages.
--strict-imports Force evaluation of imports.
--verbose Be verbose.
-v, --version Print version number and exit.
-x, --compress Compress output by removing some whitespaces.
--yui-compress Compress output using ycssmin
--max-line-len=LINELEN Max line length used by ycssmin
-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.
-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.
Report bugs to: http://github.com/cloudhead/less.js/issues
Home page: <http://lesscss.org/>
However, you can use inotify to watch for changes and this accomplishes roughly what you want:
while inotifywait -r styles.less; do
lessc -x styles.less styles.css;
For a better long-term strategy, you might want to look at Grunt which does have its own watch mode.