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# realpath — Resolve to Canonical Path
## Overview
`realpath` resolves each given pathname to its canonical absolute form
by expanding all symbolic links, resolving `.` and `..` references,
and removing extra `/` characters.
**Source**: `realpath/realpath.c` (single file)
**Origin**: BSD 4.4, University of California, Berkeley
**License**: BSD-3-Clause
## Synopsis
```
realpath [-q] [path ...]
```
## Options
| Flag | Description |
|------|-------------|
| `-q` | Quiet: suppress error messages for non-existent paths |
## Source Analysis
### Functions
| Function | Purpose |
|----------|---------|
| `main()` | Parse options and resolve loop |
| `resolve_path()` | Wrapper around `realpath(3)` |
| `set_progname()` | Extract program name from `argv[0]` |
| `print_line()` | Safe stdout writing |
| `usage()` | Print usage message |
| `warnx_msg()` | Warning without errno |
| `warn_path_errno()` | Warning with errno for path |
### Core Logic
```c
static int
resolve_path(const char *path, bool quiet)
{
char *resolved = realpath(path, NULL);
if (!resolved) {
if (!quiet)
warn("%s", path);
return 1;
}
puts(resolved);
free(resolved);
return 0;
}
```
### Main Loop
```c
int main(int argc, char *argv[])
{
bool quiet = false;
int ch, errors = 0;
while ((ch = getopt(argc, argv, "q")) != -1) {
switch (ch) {
case 'q': quiet = true; break;
default: usage();
}
}
argc -= optind;
argv += optind;
if (argc == 0)
usage();
for (int i = 0; i < argc; i++)
errors |= resolve_path(argv[i], quiet);
return errors ? 1 : 0;
}
```
Uses `realpath(path, NULL)` (POSIX.1-2008) for dynamic buffer
allocation, avoiding `PATH_MAX` limitations.
## System Calls Used
| Syscall | Purpose |
|---------|---------|
| `realpath(3)` | Canonicalize pathname |
## Examples
```sh
# Simple resolution
realpath ../foo/bar
# → /home/user/foo/bar
# Resolve symlink
ln -s /usr/local/bin target
realpath target
# → /usr/local/bin
# Quiet mode (no error for missing)
realpath -q /nonexistent/path
# (no output, exit 1)
# Multiple paths
realpath /tmp/../etc ./relative/path
```
## Exit Codes
| Code | Meaning |
|------|---------|
| 0 | All paths resolved successfully |
| 1 | One or more paths could not be resolved |
|
