The LineCache module allows one to get any line from any file, caching the lines and file information on first access to the file. Although the file may be any file, the common use is when the file is a Ruby script since parsing of the file is done to figure out where the statement boundaries are, and we also cache syntax formatting.

The routines here may be is useful when a small random sets of lines are read from a single file, in particular in a debugger to show source lines.


    require 'linecache'
    lines = LineCache::getlines('/tmp/myruby.rb')
    # The following lines have same effect as the above.
    $: << '/tmp'
    Dir.chdir('/tmp') {lines = LineCache::getlines('myruby.rb')

    line = LineCache::getline('/tmp/myruby.rb', 6)
    # Note lines[6] == line (if /tmp/myruby.rb has 6 lines)

    LineCache::update_cache   # Check for modifications of all cached files.

Git branches ruby-1.9 and ruby-2.1 for code for those respective Ruby versions. A patched version of Ruby is needed for this to work. The patches sources are here.