(oo)Rexx - Work in Progress samples

#!/usr/bin/rexx

--

-- A Generalized Rexx Filter that can be used in a pipe

--

-- Usage: rexx filter.rex builtin-or-external-function-name(arg1, arg2, ...)

--    or: rexx filter.rex < inputfile

--    or: rexx filter.rex (boolean expression) 

--

-- Note 1:

--

--    rexx (to invoke filter.rex) may or may not be required to get 

--    the redirection and piping working, dependent on the operating

--    system and the REXX implementation and/or installation setup.  

--  

-- External functions can have a simple structure, for instance: 

--          

--    rexx filter.rex "cut.rex(!line,10:5)" or filter.rex "cut(!line,10:5)"

--

--    parse arg line,poslen

--    parse var poslen pos ':' length .

--    /* possibly more logic, but return value should be a (modified)

--       line or a boolean if the function is called as an expression */

--    return delstr(line,pos,length)  

--  

-- Argument(s)/Option(s) or even all of the filter have to be quoted generally.

-- On Windows: It's best to use '"' for all of the filtere and "'" for arguments.

-- On *n?x: It's best to use "'" for all of the filter and '"' for arguments.

-- On *n?x: Redirection (< and > or >> ) doesn't seem to work all of the time.

--

-- Pipe variables:

--

-- The input line from the pipe is represented by '!line'. 

-- The running line count is represented by '!count' 

-- The total nr of lines is respresented by '!lines'

-- Using '!lines' in the filter implies buffering the input stream before 

-- any output is passed on to the next pipe stage.

--

-- Example 1: rexx filter.rex changestr(needle,!line,newneedle)

--

-- Example 2: rexx filter.rex strip(!line,'L','>')

--

-- Example 3: rexx filter.rex < somefile.txt  - just echoes the input

--

-- Example 4: rexx filter.rex (pos('>',!line)>0) - a boolean expression 

--

-- Example 5: rexx filter.rex "(!count>10)" - skips first 10 lines of input

--

-- Example 6: rexx filter.rex "(!count>!lines-10)" - shows last 10 lines of input   

--

--    rexx filter.rex <filter.rex | ,

--    rexx filter.rex (pos('-',!line)=1) | , 

--    rexx filter.rex strip(!line,'L','-')

-- 

-- will first read and echo filter.rex, 

-- then output only input lines that start with '-',

-- then strip leading comment identifier '--'. 

--

-- No copyright, no license, no guarantees, use at your own risk.

--

-- And you just read the result of the pipe above.

--

parse source . . me  

parse arg !filter

do (!filter='?' | !filter='-?' | !filter='/?' | !filter='h' | !filter='-h' | !filter='/h' | !filter='--help')

  pipe = 'rexx "'me'"<"'me'" | rexx "'me'" (pos(''-'',!line)=1) | rexx "'me'" strip(!line,''L'',''-'')'

  pipe

  exit

end

!filter = strip(strip(strip(!filter,'B',' '),'B',"'"),'B','"')  -- strip spaces and quotes



do until (lines()>0)    -- a buffered stage can delay the input stream 

  nop

end 

!buffered = (pos('!lines',!filter)>0)

if (!buffered) then do  -- buffer input stream on standard queue

  do !lines=1 by 1 while (lines()>0)

    queue linein()

  end

  !lines = queued()

  !queued = !lines

  if (!queued>0) then do        -- prefetch the 1st line queue

    parse pull !line

  end   

end

else do

  !queued = lines()

  if (!queued>0) then do        -- prefetch the 1st line from stdin

    !line = linein()

  end 

end

do !count=1 by 1 while (!queued>0)

  if (!filter = '') then do     -- no filter just echoes the input

    !out = !line

  end

  else do 

    if (substr(!filter,1,1)='(') then do

      drop !out         -- to verify !out is a var later on                                     

      interpret '!test =' !filter       -- apply the test

      if (!test) then do        -- if test yields .true it goes out

        !out = !line

      end

    end

    else do             -- apply the filter

      interpret '!out =' !filter  

    end

  end

   if (var("!out")) then do     -- only write if we have something 

     call lineout ,!out                 

  end

  if (!buffered) then do        -- if buffered, next line from queue

        !queued = queued()

        if (!queued>0) then do

          parse pull !line

        end

  end

  else do       -- not buffered, next line from stdin

    !queued = lines()

        if (!queued>0) then do

          !line = linein()

        end

  end

end

exit