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// For nanosleep(), pread()
#define _POSIX_C_SOURCE 200809L
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <time.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <sys/wait.h>
#include <assert.h>
// Warning when battery percentage is <= this
static const int WARN_PERC = 10;
// Time to sleep between checks
static const struct timespec SLEEP_SPEC = {60, 0};
// Format string with percentage %d
static const char *MESSAGE_FORMAT = "Battery at %d%%!";
static inline void parse(const char *buffer, bool *discharging, int *charge, int *full) {
while (true) {
if (memcmp(buffer, "POWER_SUPPLY_STATUS", 19) == 0) {
*discharging = memcmp(buffer + 20, "Discharging", 11) == 0;
} else if (memcmp(buffer, "POWER_SUPPLY_CHARGE_NOW", 23) == 0) {
*charge = strtol(buffer + 24, NULL, 10);
} else if (memcmp(buffer, "POWER_SUPPLY_CHARGE_FULL_DESIGN", 31) == 0) {
*full = strtol(buffer + 32, NULL, 10);
}
buffer = strchr(buffer, '\n');
if (buffer != NULL) buffer++;
else break;
}
}
int main(void) {
int fd = open("/sys/class/power_supply/BAT1/uevent", O_RDONLY);
if (fd < 0) {
perror("open");
return 1;
}
char buffer[1024];
while (true) {
ssize_t nr = pread(fd, buffer, sizeof buffer, 0);
if (nr < 0) {
perror("pread");
break;
}
bool discharging = false;
int charge = 1, full = 1;
parse(buffer, &discharging, &charge, &full);
if (full > 0 && discharging && charge * 100 / full <= WARN_PERC) {
pid_t pid = fork();
if (pid < 0) perror("fork");
else if (pid == 0) {
char msg[strlen(MESSAGE_FORMAT) + 16];
snprintf(msg, sizeof msg, MESSAGE_FORMAT, charge * 100 / full);
char *argv[4] = {"i3-nagbar", "-m", msg, NULL};
execv("/usr/bin/i3-nagbar", argv);
perror("execv");
exit(255);
} else {
int status;
do if (waitpid(pid, &status, 0) < 0 && errno == ECHILD) break;
while (!WIFEXITED(status) && !WIFSIGNALED(status));
}
}
(void)nanosleep(&SLEEP_SPEC, NULL);
}
if (close(fd) < 0) {
perror("close");
return 1;
}
}
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