107 lines
1.9 KiB
C
107 lines
1.9 KiB
C
// Simple grep. Only supports ^ . * $ operators.
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#include "types.h"
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#include "stat.h"
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#include "user.h"
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char buf[1024];
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int match(char*, char*);
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void
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grep(char *pattern, int fd)
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{
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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)) > 0){
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m += n;
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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(p == buf)
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m = 0;
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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
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main(int argc, char *argv[])
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{
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int fd, i;
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char *pattern;
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if(argc <= 1){
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printf(2, "usage: grep pattern [file ...]\n");
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exit();
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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();
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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(1, "grep: cannot open %s\n", argv[i]);
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exit();
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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();
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}
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// Regexp matcher from Kernighan & Pike,
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// The Practice of Programming, Chapter 9.
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int matchhere(char*, char*);
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int matchstar(int, char*, char*);
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int
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match(char *re, char *text)
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{
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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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{
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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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{
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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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