Remove lines from a file

The task is to demonstrate how to remove a specific line or a number of lines from a file. This should be implemented as a routine that takes three parameters (filename, starting line, and the number of lines to be removed). For the purpose of this task, line numbers and the number of lines start at one, so to remove the first two lines from the file foobar, the parameters should be: foobar, 1, 2

Empty lines are considered and should still be counted, and if the specified line is empty, it should still be removed. However, an appropriate message should appear, if an attempt is made to remove lines beyond the end of the file.

J

<lang j>removeLines=:4 :0

 'count start'=. x
 file=. boxxopen y
 lines=. <;.2]1!:1 file
 (;lines {~ <<< (start-1)+i.count) 1!:2 file

)</lang>

Thus:

<lang bash>$ cal >cal.txt $ cat cal.txt

     July 2011

Su Mo Tu We Th Fr Sa

               1  2
3  4  5  6  7  8  9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31</lang>

<lang j> 2 1 removeLines 'cal.txt'</lang>

<lang bash>$ cat cal.txt

               1  2
3  4  5  6  7  8  9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31</lang>

Note that this code assumes that the last character in the file is the line end character.

Lua

<lang lua>function remove( filename, starting_line, num_lines )

   local fp = io.open( filename, "r" )
   if fp == nil then return nil end

   content = {}
   i = 1;
   for line in fp:lines() do
       if i < starting_line or i >= starting_line + num_lines then

content[#content+1] = line end i = i + 1

end

   if i > starting_line and i < starting_line + num_lines then

print( "Warning: Tried to remove lines after EOF." )

end

   fp:close()
   fp = io.open( filename, "w+" )

   for i = 1, #content do

fp:write( string.format( "%s\n", content[i] ) )

end

   fp:close()

end</lang>