Text Fragment Extractor

/*
** fragment.c -- text fragment, public domain by tkorrovi@mail.com
** Usage: fragment /pattern/[n] [/pattern/[n]] file
** Similar to print command in ed and vi, with pattern range
** If the second pattern is omitted, prints to the end of file
** Use quotation marks when there are spaces in the argument
** Finds the first pattern, then second pattern, then calculates the
** range, so considering that make sure that the range is correct
*/

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

FILE *file;
char line [FILENAME_MAX], pattern [FILENAME_MAX], *last;

char *gs (char *s, int n, FILE *stream)
{
	char *output;

	output = fgets (s, n, stream);
	if (ferror (stream)) exit (1);
	return output;
}

int ps (const char *s, FILE *stream)
{
	int output;

	output = fputs (s, stream);
	if (ferror (stream)) exit (1);
	return output;
}

long findline (char *argument, long *i, int start)
{
	long n = 0;

	if (strlen (argument) < 2) exit (1);
	strcpy (pattern, argument + 1);
	if (strrchr (pattern, '/') == NULL) exit (1);
	n = atoi (strrchr (pattern, '/') + 1);
	*strrchr (pattern, '/') = 0;
	for (*i = start; 
		(last = gs (line, sizeof line, file)) != NULL; 
		(*i)++)
	{
		if (strstr (line, pattern) != NULL 
			|| !strcmp (pattern, ""))
		{
			break;
		}
	}
	if (last == NULL) exit (1);
	return n;
}

int main (int argc, char *argv [])
{
	long l1 = 0, l2 = 0, n1, n2, i;

	if (argc < 3 || argc > 4) return 1;
	if ((file = fopen (argv [argc - 1], "r")) == 0) return 1;
	n1 = findline (argv [1], &l1, 1);
	if (argc > 3) n2 = findline (argv [2], &l2, l1 + 1);
	if (l2 + n2 < l1 + n1 || l1 + n1 < 1 
		|| l2 + n2 < 1)
	{
		return 1;
	}
	if (fseek (file, 0, SEEK_SET)) return 1;
	if (l1 + n1 > 1)
	{
		for (i = 1; i < l1 + n1; i++)
		{
			last = gs (line, sizeof line, file);
		}
	}
 	if (last == NULL) return 1;	
	if (argc == 3)
	{
		while (gs (line, sizeof line, file) != NULL)
		{
			ps (line, stdout);
		}
	}
	else
	{
		for (i = l1 + n1; i <= l2 + n2; i++)
		{
			last = gs (line, sizeof line, file);
			if (last == NULL) break;
			ps (line, stdout);
		}
	}
	return 0;
}