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# pwd — Print Working Directory
## Overview
`pwd` prints the absolute pathname of the current working directory.
It supports logical mode (using `$PWD`) and physical mode (resolving
symlinks). Logical mode is the default, with fallback to physical
if validation fails.
**Source**: `pwd/pwd.c` (single file)
**Origin**: BSD 4.4, University of California, Berkeley
**License**: BSD-3-Clause
## Synopsis
```
pwd [-L | -P]
```
## Options
| Flag | Description |
|------|-------------|
| `-L` | Logical: use `$PWD` (default) |
| `-P` | Physical: resolve all symlinks |
When both are specified, the last one wins.
## Source Analysis
### Functions
| Function | Purpose |
|----------|---------|
| `main()` | Parse options and dispatch |
| `getcwd_logical()` | Validate and use `$PWD` |
| `getcwd_physical()` | Resolve via `getcwd(3)` |
| `usage()` | Print usage message |
### Logical Mode (Default)
```c
static char *
getcwd_logical(void)
{
const char *pwd = getenv("PWD");
/* Must be set and absolute */
if (!pwd || pwd[0] != '/')
return NULL;
/* Must not contain "." or ".." components */
if (contains_dot_components(pwd))
return NULL;
/* Must refer to the same directory as "." */
struct stat pwd_sb, dot_sb;
if (stat(pwd, &pwd_sb) < 0 || stat(".", &dot_sb) < 0)
return NULL;
if (pwd_sb.st_dev != dot_sb.st_dev ||
pwd_sb.st_ino != dot_sb.st_ino)
return NULL;
return strdup(pwd);
}
```
The `$PWD` validation ensures:
1. The value is an absolute path
2. It contains no `.` or `..` components
3. The path resolves to the same inode as `.`
### Physical Mode
```c
static char *
getcwd_physical(void)
{
/* POSIX: getcwd(NULL, 0) dynamically allocates */
return getcwd(NULL, 0);
}
```
Uses the POSIX extension `getcwd(NULL, 0)` which allocates the
returned buffer dynamically, avoiding fixed-size buffer limitations.
### Main Logic
```c
int main(int argc, char *argv[])
{
int mode = MODE_LOGICAL; /* Default: logical */
while ((ch = getopt(argc, argv, "LP")) != -1) {
switch (ch) {
case 'L': mode = MODE_LOGICAL; break;
case 'P': mode = MODE_PHYSICAL; break;
default: usage();
}
}
char *cwd;
if (mode == MODE_LOGICAL) {
cwd = getcwd_logical();
if (!cwd)
cwd = getcwd_physical(); /* Fallback */
} else {
cwd = getcwd_physical();
}
if (!cwd)
err(1, "getcwd");
puts(cwd);
free(cwd);
return 0;
}
```
## System Calls Used
| Syscall | Purpose |
|---------|---------|
| `getcwd(3)` | Physical working directory |
| `stat(2)` | Validate `$PWD` against `.` |
| `getenv(3)` | Read `$PWD` environment variable |
## Examples
```sh
# Default (logical)
pwd
# /home/user/projects/mylink (preserves symlink name)
# Physical
pwd -P
# /home/user/actual/path (resolved symlinks)
# Demonstrate difference
cd /tmp
ln -s /usr/local/share mylink
cd mylink
pwd -L # → /tmp/mylink
pwd -P # → /usr/local/share
```
## Exit Codes
| Code | Meaning |
|------|---------|
| 0 | Success |
| 1 | Error (cannot determine directory) |
|
