Simple text file reader-viewer line by line for Linux | fpc

// Simple text file reader-viewer line by line for Linux | in free pascal |

program fr;
// programmer: Aleksandar Josifoski     josifoski@gmail.com
// reading text file line by line
// j for next k for previous g for first G for last line q for quit
{$mode objfpc}{$H+}

uses Unix, keyboard, sysutils;

var
   f : Text;
   L, i, j : Longint;
   ar: array[1..100000] of String;
   si, sj : String;
   K : TKeyEvent;
   stcomm : String;

begin
   InitKeyBoard;
   if  (ParamStr(1)='') or (FileExists(ParamStr(1))=false) then begin
                              writeln('Simple file reader-viewer line by line');
                              writeln('Usage is fr YourFile');
                              writeln('Shortcuts: j next, k previous, g first, G last line, q or ESC quit');
                              DoneKeyBoard;
                              Halt;
                           end;
   stcomm:='tr -s ''\n'' <'+ParamStr(1)+' >frfile';
   L:= FpSystem(stcomm);
   L:= FpSystem('clear');
   AssignFile(f, 'frfile');
   reset(f);
   j:=0;
   while not(eof(f)) do begin
     j:=j+1;
     readln(f, ar[j]);
   end; // while
   CloseFile(f);
   if j=0 then begin
                 writeln('empty file, exit');
                 DoneKeyBoard;
                 Halt;
               end;
   i:=1;
   str(j, sj);
   str(i, si);
   writeln(si+'/'+sj);
   writeln();
   writeln();
   write(ar[i]);
   repeat
    K:=GetKeyEvent;
    K:=TranslateKeyEvent(K);
            case GetKeyEventChar(K) of
             'j' : if i < j then begin
                      L:= FpSystem('clear');
                      i:=i+1;
                      str(i, si);
                      writeln(si+'/'+sj);
                      writeln();
                      writeln();
                      write(ar[i]);
                    end;
             'k' : if i > 1 then begin
                      L:= FpSystem('clear');
                      i:=i-1;
                      str(i, si);
                      writeln(si+'/'+sj);
                      writeln();
                      writeln();
                      write(ar[i]);
                    end;
             'g' :  begin
                      L:= FpSystem('clear');
                      i:=1;
                      str(i, si);
                      writeln(si+'/'+sj);
                      writeln();
                      writeln();
                      write(ar[i]);
                    end;
             'G' :  begin
                      L:= FpSystem('clear');
                      i:=j;
                      str(i, si);
                      writeln(si+'/'+sj);
                      writeln();
                      writeln();
                      write(ar[i]);
                    end;
             'q' : L:= FpSystem('clear');
             #27 : L:= FpSystem('clear');
            end;
   until (GetKeyEventChar(K)='q') or (GetKeyEventChar(K)=#27);
   DoneKeyBoard;
end.