#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdbool.h>
#include <errno.h>
#include <err.h>
#include <sysexits.h>
#include <sys/stat.h>
#include <sys/fcntl.h>
#include <sys/param.h>
#include <sys/time.h>
void usage(void);
int
main(int argc, char * argv[])
{
struct stat sb;
char *newcontent = NULL;
size_t newcontentlength = 0;
char *oldcontent = NULL;
int ret;
int dstfd;
const char *dst = NULL;
ssize_t readsize, writesize;
int i;
if (argc < 2) {
usage();
}
dst = argv[1];
for (i = 2; i < argc; i++) {
newcontentlength += strlen(argv[i]) + 1 ;
}
newcontentlength += 1;
newcontent = malloc(newcontentlength);
if (newcontent == NULL) {
err(EX_UNAVAILABLE, "malloc() failed");
}
newcontent[0] = '\0';
for (i = 2; i < argc; i++) {
strlcat(newcontent, argv[i], newcontentlength);
if (i < argc - 1) {
strlcat(newcontent, " ", newcontentlength);
} else {
strlcat(newcontent, "\n", newcontentlength);
}
}
dstfd = open(dst, O_RDWR | O_CREAT | O_APPEND, DEFFILEMODE);
if (dstfd < 0) {
err(EX_NOINPUT, "open(%s)", dst);
}
ret = fstat(dstfd, &sb);
if (ret < 0) {
err(EX_NOINPUT, "fstat(%s)", dst);
}
if (!S_ISREG(sb.st_mode)) {
err(EX_USAGE, "%s is not a regular file", dst);
}
if (sb.st_size != newcontentlength) {
goto replace;
}
oldcontent = malloc(newcontentlength);
if (oldcontent == NULL) {
err(EX_UNAVAILABLE, "malloc(%lu) failed", newcontentlength);
}
readsize = read(dstfd, oldcontent, newcontentlength);
if (readsize == -1) {
err(EX_UNAVAILABLE, "read() failed");
} else if (readsize != newcontentlength) {
errx(EX_UNAVAILABLE, "short read of file");
}
if (0 == memcmp(oldcontent, newcontent, newcontentlength)) {
free(oldcontent);
ret = close(dstfd);
if (ret < 0) {
err(EX_UNAVAILABLE, "close() failed");
}
exit(0);
}
replace:
ret = ftruncate(dstfd, 0);
if (ret < 0) {
err(EX_UNAVAILABLE, "ftruncate() failed");
}
writesize = write(dstfd, newcontent, newcontentlength);
if (writesize == -1) {
err(EX_UNAVAILABLE, "write() failed");
} else if (writesize != newcontentlength) {
errx(EX_UNAVAILABLE, "short write of file");
}
ret = close(dstfd);
if (ret < 0) {
err(EX_NOINPUT, "close(dst)");
}
return 0;
}
void
usage(void)
{
fprintf(stderr, "Usage: %s <dst> <new> <contents> <...>\n",
getprogname());
exit(EX_USAGE);
}