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#include <stdio.h>
#include <string.h>
/* The C Programming Language: 2nd Edition
*
* Exercise 7-7: Modify the pattern finding program of Chapter 5 to take its
* input from a set of named files or, if no files are named as arguments, from
* the standard input. Should the file name be printed when a matching line is
* found?
*
* Notes: The program in question is on page 117 of the book. Note from various
* errata documents (found around the Web) that the line:
*
* while (c = *++argv[0])
*
* is not correct, since it's attempting to modify something that the standard
* makes no guarantee to be modifiable. So to monkey-patch it, I used the
* typical 'i is the iterator' variable.
*
* The biggest obstacle to this exercise was correcting the original code from
* page 117.
*
* A gotcha that I came across is figuring out how to make use of or save the
* pattern that the user will be searching for. I could have allocated a
* character array (string) and stored it directly, but it made more sense to
* create another character pointer and leverage the storage that argv was
* already making use of. So I ended up with two pointers to the same data,
* like hardlinks in a *nix filesystem.
*
* The filename that a pattern is found in *should* be present, because it's
* trivial to match text in multiple files. Generally when one is looking for
* text, they want to *edit* that text, and editing it is fruitless if you
* don't have the file name handy. That said, putting it behind an option is a
* great way to add extensibility to it.
*/
#define MAXLINE 1000
int get_line(char *line, int max, FILE *f);
int main(int argc, char *argv[]) {
char line[MAXLINE];
long lineno = 0;
int c, except = 0, number = 0, showfiles = 0, found = 0, i = 0;
char *pattern = NULL;
char *filename = NULL;
FILE *infile = NULL;
if (argc < 2) {
printf("pwf: please specify a pattern to search for\n");
return 1;
}
while (--argc > 0 && (*++argv)[0] == '-') {
i = 0;
while ((c = (*argv)[++i]) != '\0') {
switch (c) {
case 'x':
except = 1;
break;
case 'n':
number = 1;
break;
case 'f':
showfiles = 1;
break;
case 'h':
printf("Usage: pwf [-{xnfh}] PATTERN [file] [file] ...\n");
break;
default:
printf("pwf: illegal option %c\n", c);
argc = 0;
found = -1;
break;
}
}
}
/* The first argument _after_ options should be the pattern; without
* a pattern we shouldn't be accepting anything at all.
*/
pattern = *argv;
/* This handles the edge-case of no file names given. It's somewhat of an
* ugly hack since it fools argc, but it gets the job done. */
if (argc == 1) {
infile = stdin;
filename = "stdin";
argc++;
}
while (--argc > 0) {
/* Now we handle the case of a given filename */
if (infile != stdin) {
filename = *(++argv);
infile = fopen(filename, "r");
if (filename == NULL || infile == NULL) {
printf("File %s could not be opened; falling back to stdin...\n", filename);
infile = stdin;
filename = "stdin";
}
}
/* We have _some_ usable file to work with, now. Let's do the thing */
lineno = 0;
while (get_line(line, MAXLINE, infile) > 0) {
lineno++;
if ((strstr(line, pattern) != NULL) != except) {
if (showfiles) {
printf("%s:", filename);
}
if (number) {
printf("%ld:", lineno);
}
printf("%s", line);
found++;
}
}
}
return found;
}
int get_line(char *s, int lim, FILE *f) {
int c, i;
for (i = 0; i < lim - 1 && (c = getc(f)) != EOF && c != '\n'; ++i) {
*s++ = c;
}
if (c == '\n') {
*s++ = c;
i++;
}
*s = '\0';
return i;
}
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