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# sleep — Suspend Execution for an Interval
## Overview
`sleep` pauses for the specified duration. It supports fractional seconds,
multiple arguments (accumulated), unit suffixes (`s`, `m`, `h`, `d`),
and `SIGINFO`/`SIGUSR1` for progress reporting.
**Source**: `sleep/sleep.c` (single file)
**Origin**: BSD 4.4, University of California, Berkeley
**License**: BSD-3-Clause
## Synopsis
```
sleep number[suffix] ...
```
## Options
No flags. Arguments are durations with optional unit suffixes.
## Unit Suffixes
| Suffix | Meaning | Multiplier |
|--------|---------|------------|
| `s` (default) | Seconds | 1 |
| `m` | Minutes | 60 |
| `h` | Hours | 3600 |
| `d` | Days | 86400 |
## Source Analysis
### Functions
| Function | Purpose |
|----------|---------|
| `main()` | Parse arguments and sleep loop |
| `parse_interval()` | Parse numeric value with unit suffix |
| `scale_interval()` | Apply unit multiplier with overflow check |
| `seconds_to_timespec()` | Convert float seconds to `struct timespec` |
| `seconds_from_timespec()` | Extract seconds from `struct timespec` |
| `install_info_handler()` | Set up `SIGINFO`/`SIGUSR1` handler |
| `report_remaining()` | Print remaining time on signal |
| `die()` / `die_errno()` | Error handling |
| `usage()` | Print usage and exit |
### Argument Accumulation
Multiple arguments are summed:
```c
int main(int argc, char *argv[])
{
double total = 0.0;
for (int i = 1; i < argc; i++) {
double interval = parse_interval(argv[i]);
total += interval;
}
if (total > (double)TIME_T_MAX)
die("total sleep duration too large");
struct timespec ts = seconds_to_timespec(total);
install_info_handler();
/* Sleep loop with EINTR restart */
while (nanosleep(&ts, &ts) < 0) {
if (errno != EINTR)
die_errno("nanosleep");
/* SIGINFO handler may have reported progress */
}
return 0;
}
```
### Interval Parsing
```c
static double
parse_interval(const char *arg)
{
char *end;
double val = strtod(arg, &end);
if (end == arg || val < 0)
die("invalid time interval: %s", arg);
/* Apply unit suffix */
if (*end != '\0') {
val = scale_interval(val, *end);
end++;
}
if (*end != '\0')
die("invalid time interval: %s", arg);
return val;
}
static double
scale_interval(double val, char unit)
{
switch (unit) {
case 's': return val;
case 'm': return val * 60.0;
case 'h': return val * 3600.0;
case 'd': return val * 86400.0;
default:
die("invalid unit: %c", unit);
}
}
```
### Progress Reporting
```c
static volatile sig_atomic_t info_requested;
static void
signal_handler(int sig)
{
(void)sig;
info_requested = 1;
}
static void
install_info_handler(void)
{
struct sigaction sa = {
.sa_handler = signal_handler,
.sa_flags = 0,
};
sigemptyset(&sa.sa_mask);
#ifdef SIGINFO
sigaction(SIGINFO, &sa, NULL);
#endif
sigaction(SIGUSR1, &sa, NULL);
}
static void
report_remaining(const struct timespec *remaining)
{
double secs = seconds_from_timespec(remaining);
fprintf(stderr, "sleep: about %.1f second(s) remaining\n", secs);
info_requested = 0;
}
```
When `nanosleep` returns with `EINTR` and the remaining time is in `ts`,
the handler flag is checked and progress is reported before restarting.
### Overflow Protection
```c
static struct timespec
seconds_to_timespec(double sec)
{
struct timespec ts;
if (sec >= (double)TIME_T_MAX) {
ts.tv_sec = TIME_T_MAX;
ts.tv_nsec = 0;
} else {
ts.tv_sec = (time_t)sec;
ts.tv_nsec = (long)((sec - ts.tv_sec) * 1e9);
}
return ts;
}
```
## System Calls Used
| Syscall | Purpose |
|---------|---------|
| `nanosleep(2)` | Sleep with nanosecond precision |
| `sigaction(2)` | Install signal handlers |
## Examples
```sh
# Sleep 5 seconds
sleep 5
# Fractional seconds
sleep 0.5
# With units
sleep 2m # 2 minutes
sleep 1.5h # 90 minutes
sleep 1d # 24 hours
# Multiple arguments (accumulated)
sleep 1m 30s # 90 seconds total
# Check remaining time (send SIGUSR1 from another terminal)
kill -USR1 $(pgrep sleep)
# → "sleep: about 42.3 second(s) remaining"
```
## Exit Codes
| Code | Meaning |
|------|---------|
| 0 | Success (slept for full duration) |
| 1 | Error (invalid argument) |
## Differences from GNU sleep
- POSIX-compliant with BSD extensions
- Supports `SIGINFO` (on systems that have it, otherwise `SIGUSR1`)
- Same unit suffix support (`s`, `m`, `h`, `d`)
- Multiple arguments are accumulated (same as GNU)
|
