how to define script interpreter with shebang

Question

It is clear that one can use the

#!/usr/bin/perl

shebang notation in the very first line of a script to define the interpreter. However, this presupposes an interpreter that ignores hashmark-starting lines as comments. How can one use an interpreter that does not have this feature?

Answer 1

With a wrapper that removes the first line and calls the real interpreter with the remainder of the file. It could look like this:

#!/bin/sh

# set your "real" interpreter here, or use cat for debugging
REALINTERP="cat"

tail -n +2 $1 | $REALINTERP

Other than that: In some cases ignoring the error message about that first line could be an option.

Last resort: code support for the comment char of your interpreter into the kernel.

Answer 2

I think the first line is interpreted by the operating system. The interpreter will be started and the name of the script is handed down to the script as its first parameter. The following script 'first.myint' calls the interpreter 'myinterpreter' which is the executable from the C program below.

#!/usr/local/bin/myinterpreter
% 1 #########
2 xxxxxxxxxxx
333
444
% the last comment

The sketch of the personal interpreter:

#include <errno.h>
#include <stdio.h> 
#include <stdlib.h>
#include <string.h>

#define BUFFERSIZE  256                         /* input buffer size */

  int
main ( int argc, char *argv[] )
{
  char    comment_leader  = '%';                /* define the coment leader */
  char    *line = NULL;
  size_t  len   = 0;
  ssize_t read;
  //  char  buffer[BUFFERSIZE];

  // argv[0] : the name of this executable
  // argv[1] : the name the script calling this executable via shebang

  FILE  *input;                                 /* input-file pointer */
  char  *input_file_name = argv[1];             /* the script name    */

  input = fopen( input_file_name, "r" );
  if ( input == NULL ) {
    fprintf ( stderr, "couldn't open file '%s'; %s\n",
        input_file_name, strerror(errno) );
    exit (EXIT_FAILURE);
  }

  while ((read = getline(&line, &len, input)) != -1) {
    if ( line[0] != comment_leader ) {
      printf( "%s", line );                     /* print line as a test */
    }
    else {
      printf ( "Skipped a comment!\n" );
    }
  }

  free(line);

  if( fclose(input) == EOF ) {                  /* close input file   */
    fprintf ( stderr, "couldn't close file '%s'; %s\n",
        input_file_name, strerror(errno) );
    exit (EXIT_FAILURE);
  }

  return EXIT_SUCCESS;
}   /* ----------  end of function main  ---------- */

Now call the script (made executable before) and see the output:

...~> ./first.myint
#!/usr/local/bin/myinterpreter
Skipped a comment!
2 xxxxxxxxxxx
333
444
Skipped a comment!