Apply.png Most RISC OS users know by now that you can manipulate the text in a StrongED window by SHIFT-dragging a script onto the apply icon, as shown left, on the window's smarticon bar. CTRL-dragging will instead put the modified text in a new StrongED window without overwriting the old (in fact these behaviours can be altered by editing StrongED's BaseMode Modefile). Dragging scripts is a powerful feature; it means that you are not limited to the off-the-peg tools offered by StrongED. These notes are intended to show you how to make your own tools using Lua scripts.
lua.png The script must either have the filetype lua (&18C), as shown by the icon at the left, or it should be a text file whose first is line begins #! lua , for StrongED to recognize it. The script can read the contents of the StrongED window from the variable

whose value should be treated as a filename. The new contents of the StrongED window is created by the script's output, typically using the functions

 print   io.write
Consider this script:

#! lua
    local n, inc = 10, 10
    for line in io.lines (arg[1]) do
        print (n, line)
        n += inc
    end -- for
This numbers the lines starting at 10, with increments of 10. The io.lines iterator is very useful and concise but it can only be used if the data your script is supposed to capture always lies on a single line. If the data extends over many lines it may be more convenient to read in the whole text as a single string as in this example.

    -- Print the phrases beginning Hello and ending Dolly.
    local input, read in io
    input (arg[1])  -- switch input to arg[1]
    local text = read "*all"
    input ( )       -- reset back to stdin
    for phrase in text:gmatch "(Hello.-Dolly)" do
       print (phrase)
    end -- for
The point is that when you find Hello you do not know how many further lines to search for a Dolly , which would make the line by line approach rather clumsy.
Before you write any code, you should consider which approach to adopt: line by line with io.lines , or read in the whole text with . As a matter of style note the use of local variables wherever possible, so that an item in a library is only looked up once at most. Avoiding performing the same calculation twice, if necessary by creating more variables, should be an instinct.