Command Line Flags in Pascal

Here’s the translation of the Go code to Pascal, with explanations in Markdown format suitable for Hugo:

Command-line flags are a common way to specify options for command-line programs. For example, in wc -l the -l is a command-line flag.

Pascal doesn’t have a built-in package for parsing command-line flags like Go does. However, we can implement a simple version of this functionality ourselves. Here’s an example of how we might do that:

program CommandLineFlags;

uses
  SysUtils;

var
  WordFlag: string = 'foo';
  NumbFlag: Integer = 42;
  ForkFlag: Boolean = False;
  SvarFlag: string = 'bar';

procedure ParseCommandLine;
var
  i: Integer;
  arg: string;
begin
  for i := 1 to ParamCount do
  begin
    arg := ParamStr(i);
    if arg.StartsWith('--word=') then
      WordFlag := arg.Substring(7)
    else if arg.StartsWith('--numb=') then
      NumbFlag := StrToIntDef(arg.Substring(7), 42)
    else if arg = '--fork' then
      ForkFlag := True
    else if arg.StartsWith('--svar=') then
      SvarFlag := arg.Substring(7);
  end;
end;

begin
  ParseCommandLine;

  WriteLn('word: ', WordFlag);
  WriteLn('numb: ', NumbFlag);
  WriteLn('fork: ', ForkFlag);
  WriteLn('svar: ', SvarFlag);
  Write('tail: ');
  for var i := 1 to ParamCount do
  begin
    var arg := ParamStr(i);
    if not (arg.StartsWith('--word=') or arg.StartsWith('--numb=') or 
            (arg = '--fork') or arg.StartsWith('--svar=')) then
      Write(arg, ' ');
  end;
  WriteLn;
end.

In this Pascal program, we define variables for each flag with default values. The ParseCommandLine procedure iterates through the command-line arguments and updates the flag values accordingly.

To experiment with this program, compile it and then run the resulting executable directly.

$ fpc command_line_flags.pas
$ ./command_line_flags --word=opt --numb=7 --fork --svar=flag
word: opt
numb: 7
fork: True
svar: flag
tail:

Note that if you omit flags, they automatically take their default values:

$ ./command_line_flags --word=opt
word: opt
numb: 42
fork: False
svar: bar
tail:

Trailing positional arguments can be provided after any flags:

$ ./command_line_flags --word=opt a1 a2 a3
word: opt
numb: 42
fork: False
svar: bar
tail: a1 a2 a3

This Pascal implementation is more basic than the Go version. It doesn’t automatically generate help text or handle errors as robustly. For a more full-featured command-line parsing in Pascal, you might want to look into third-party libraries or implement more sophisticated parsing yourself.