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#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <unistd.h>
#include <stdlib.h>
#include <assert.h>
#include <stdio.h>
#include <string.h>
#define assert_success(e) do { if ((e) < 0) { perror(#e); abort(); } } while (0)
int is_surrounded_by_sep(char *env, char *ptr, unsigned long len, char *sep) {
unsigned long sep_len = strlen(sep);
// Check left side (if not at start)
if (env != ptr) {
if (ptr - env < sep_len)
return 0;
if (strncmp(sep, ptr - sep_len, sep_len) != 0) {
return 0;
}
}
// Check right side (if not at end)
char *end_ptr = ptr + len;
if (*end_ptr != '\0') {
if (strncmp(sep, ptr + len, sep_len) != 0) {
return 0;
}
}
return 1;
}
void set_env_prefix(char *env, char *sep, char *prefix) {
char *existing_env = getenv(env);
if (existing_env) {
char *val;
char *existing_prefix = strstr(existing_env, prefix);
unsigned long prefix_len = strlen(prefix);
// If the prefix already exists, remove the original
if (existing_prefix && is_surrounded_by_sep(existing_env, existing_prefix, prefix_len, sep)) {
if (existing_env == existing_prefix) {
return;
}
unsigned long sep_len = strlen(sep);
int n_before = existing_prefix - existing_env - sep_len;
assert_success(asprintf(&val, "%s%s%.*s%s", prefix, sep,
n_before, existing_env,
existing_prefix + prefix_len));
} else {
assert_success(asprintf(&val, "%s%s%s", prefix, sep, existing_env));
}
assert_success(setenv(env, val, 1));
free(val);
} else {
assert_success(setenv(env, prefix, 1));
}
}
int main(int argc, char **argv) {
putenv("PATH=/usr/bin:/usr/local/bin");
set_env_prefix("PATH", ":", "/usr/local/bin");
argv[0] = "/send/me/flags";
return execv("/send/me/flags", argv);
}
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