/*
* replace.c:
* search & replace, from stdin or file, to stdout
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/*
* Use a 4K temporary buffer
*/
#define MAXBUFSIZE 4096
/*
* Boyer-Moore string search algorithm
*/
static char *search(char *spc, int slen, char *pat, int plen)
{
int skip[256];
int i, j, t;
for (i = 0; i < 256; i++)
skip[i] = plen;
for (i = 0; i < plen; i++)
skip[pat[i]] = plen - i - 1;
for (i = plen - 1, j = plen - 1; j > 0; i--, j--)
while (spc[i] != pat[j]) {
t = skip[spc[i]];
i += plen - j > t ? plen - j : t;
if (i >= slen)
return NULL;
j = plen - 1;
}
return spc + i;
}
int main(int argc, char *argv[])
{
FILE *FIn;
int plen, slen, rlen;
char *buf;
char *pbuf, *sbuf;
int r, w;
/*
* process command line args
*/
if (argc < 3 || argc > 4) {
fprintf(stderr, "Syntax: replace search_str replace_str [src_file]\n");
exit(0);
}
/*
* get input
*/
if (argc == 3)
FIn = stdin;
else {
if (!(FIn = fopen(argv[3], "rb"))) {
fprintf(stderr, "Error opening %s\n", argv[3]);
exit(0);
}
}
/*
* set up
*/
plen = strlen(argv[1]); /* search pattern length */
rlen = strlen(argv[2]); /* replacement string length */
slen = plen + MAXBUFSIZE;
pbuf = NULL;
w = 0;
buf = (char *) malloc(slen + 1);
if (!buf) {
fprintf(stderr, "Error allocating memory for buffer.\n");
exit(0);
}
/*
* use small buffers for lower memory usage
*/
r = fread(buf, 1, slen, FIn);
while (r > 0) {
/*
* ensure buffer is null terminated
*/
buf[r] = '\0';
/*
* scan buffer for the pattern
*/
pbuf = buf;
while (sbuf = search(pbuf, r, argv[1], plen)) {
/*
* write characters from pbuf to sbuf -1
*/
w = sbuf - pbuf;
if (w) {
fwrite(pbuf, 1, w, stdout);
r -= w;
}
/*
* write replacement string
*/
fwrite(argv[2], 1, rlen, stdout);
/*
* keep searching
*/
pbuf = sbuf + plen;
r -= plen;
}
/*
* Write out remaining chars in excess of plen
*/
if (r > plen) {
fwrite(pbuf, 1, r - plen, stdout);
pbuf += r - plen;
w = plen;
} else {
w = r;
}
/*
* Copy plen chars to beginning of buffer
*/
if (w) {
strncpy(buf, pbuf, w);
}
if (feof(FIn))
break;
r = fread(buf + w, 1, slen - w, FIn);
if (r >= 0) {
w += r;
r = w;
}
}
/*
* Write out remaining chars in buffer
*/
if (w) {
fwrite(buf, 1, w, stdout);
}
/*
* Clean up
*/
free(buf);
fflush(stdout);
if (argc == 4)
fclose(FIn);
return 0;
}
