98 lines
1.9 KiB
C
98 lines
1.9 KiB
C
// Simple grep. Only supports ^ . * $ operators.
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#include "kernel/types.h"
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#include "kernel/stat.h"
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#include "user/user.h"
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char buf[1024];
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int match(char *, char *);
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void grep(char *pattern, int fd) {
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int n, m;
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char *p, *q;
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m = 0;
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while ((n = read(fd, buf + m, sizeof(buf) - m - 1)) > 0) {
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m += n;
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buf[m] = '\0';
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p = buf;
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while ((q = strchr(p, '\n')) != 0) {
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*q = 0;
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if (match(pattern, p)) {
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*q = '\n';
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write(1, p, q + 1 - p);
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}
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p = q + 1;
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}
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if (m > 0) {
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m -= p - buf;
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memmove(buf, p, m);
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}
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}
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}
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int main(int argc, char *argv[]) {
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int fd, i;
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char *pattern;
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if (argc <= 1) {
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fprintf(2, "usage: grep pattern [file ...]\n");
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exit(1);
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}
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pattern = argv[1];
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if (argc <= 2) {
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grep(pattern, 0);
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exit(0);
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}
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for (i = 2; i < argc; i++) {
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if ((fd = open(argv[i], 0)) < 0) {
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printf("grep: cannot open %s\n", argv[i]);
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exit(1);
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}
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grep(pattern, fd);
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close(fd);
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}
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exit(0);
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}
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// Regexp matcher from Kernighan & Pike,
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// The Practice of Programming, Chapter 9, or
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// https://www.cs.princeton.edu/courses/archive/spr09/cos333/beautiful.html
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int matchhere(char *, char *);
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int matchstar(int, char *, char *);
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int match(char *re, char *text) {
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if (re[0] == '^')
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return matchhere(re + 1, text);
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do { // must look at empty string
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if (matchhere(re, text))
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return 1;
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} while (*text++ != '\0');
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return 0;
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}
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// matchhere: search for re at beginning of text
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int matchhere(char *re, char *text) {
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if (re[0] == '\0')
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return 1;
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if (re[1] == '*')
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return matchstar(re[0], re + 2, text);
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if (re[0] == '$' && re[1] == '\0')
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return *text == '\0';
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if (*text != '\0' && (re[0] == '.' || re[0] == *text))
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return matchhere(re + 1, text + 1);
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return 0;
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}
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// matchstar: search for c*re at beginning of text
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int matchstar(int c, char *re, char *text) {
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do { // a * matches zero or more instances
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if (matchhere(re, text))
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return 1;
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} while (*text != '\0' && (*text++ == c || c == '.'));
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return 0;
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}
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