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#include <errno.h>
#include <grp.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
struct passwd *pwd;
errno = 0;
if(argc == 2)
pwd = getpwnam(argv[1]);
else
pwd = getpwuid(getuid());
if(pwd == NULL) {
fprintf(stderr,
"groups: %s: %s\n",
argv[1],
errno == 0 ? "user not found" : strerror(errno));
return 1;
}
int ngroups = 10;
gid_t *groups = malloc(ngroups * sizeof(*groups));
if(getgrouplist(pwd->pw_name, pwd->pw_gid, groups, &ngroups) == -1) {
/* the user is a member of more than ngroups groups */
ngroups += 10;
groups = malloc(ngroups * sizeof(*groups));
getgrouplist(pwd->pw_name, pwd->pw_gid, groups, &ngroups);
}
struct group *gr;
for(int i = 0; i < ngroups; i++) {
gr = getgrgid(groups[i]);
printf("%s ", gr->gr_name);
}
printf("\n");
free(groups);
return 0;
}
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