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/*-
* SPDX-License-Identifier: BSD-3-Clause
*
* Copyright (c) 1991, 1993, 1994
* The Regents of the University of California. All rights reserved.
* Copyright (c) 2026 Dag-Erling Smørgrav
* Copyright (c) 2026 Project Tick. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
/*
* Linux-native port of FreeBSD pwd(1).
*
* BSD dependency removed:
* - <sys/param.h> / MAXPATHLEN: replaced by dynamic getcwd(NULL, 0)
* which is POSIX.1-2008 and supported by both glibc and musl.
*
* Logical (-L) and physical (-P) semantics are fully POSIX and portable;
* no BSD-specific kernel calls are involved.
*/
#include <sys/stat.h>
#include <errno.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
struct options {
bool logical;
};
static const char *progname = "pwd";
static void usage(void) __attribute__((noreturn));
static char *getcwd_logical(void);
static char *getcwd_physical(void);
/*
* Attempt to return the logical working directory from $PWD.
*
* Returns a pointer to the $PWD string (not heap-allocated; do not free)
* if $PWD is set, absolute, contains no /./ or /../ components, and
* stat(2) confirms it refers to the same inode as ".".
*
* Returns NULL on any validation failure; callers must fall through to
* getcwd_physical().
*/
static char *
getcwd_logical(void)
{
struct stat log_st, phy_st;
char *pwd, *p, *q;
/* $PWD must be set and must be an absolute path. */
if ((pwd = getenv("PWD")) == NULL || *pwd != '/')
return (NULL);
/*
* $PWD must not contain /./ or /../ components.
* Walk each slash-delimited segment and reject "." and "..".
*/
for (p = pwd + 1; *p != '\0'; p = q) {
/* p points to the first character of a path segment. */
for (q = p; *q != '\0' && *q != '/'; q++)
/* advance to end of segment */;
size_t seglen = (size_t)(q - p);
if (seglen == 1 && p[0] == '.')
return (NULL);
if (seglen == 2 && p[0] == '.' && p[1] == '.')
return (NULL);
/* Skip the slash separator for next iteration. */
if (*q == '/')
q++;
}
/* $PWD must refer to the same inode/device as ".". */
if (stat(pwd, &log_st) != 0 || stat(".", &phy_st) != 0)
return (NULL);
if (log_st.st_dev != phy_st.st_dev || log_st.st_ino != phy_st.st_ino)
return (NULL);
return (pwd);
}
/*
* Return the physical working directory via getcwd(3).
*
* POSIX.1-2008 §2.2.3 allows getcwd(NULL, 0) which dynamically allocates
* a buffer of the required size. Both glibc and musl implement this.
* The caller is responsible for free()ing the returned string.
*
* Returns NULL with errno set on failure.
*/
static char *
getcwd_physical(void)
{
return (getcwd(NULL, 0));
}
static void
usage(void)
{
(void)fprintf(stderr, "usage: %s [-L | -P]\n", progname);
exit(1);
}
int
main(int argc, char *argv[])
{
struct options opts;
char *pwd;
int ch;
if (argv[0] != NULL && argv[0][0] != '\0') {
const char *slash = strrchr(argv[0], '/');
progname = (slash != NULL && slash[1] != '\0') ?
slash + 1 : argv[0];
}
opts.logical = true;
while ((ch = getopt(argc, argv, "LP")) != -1) {
switch (ch) {
case 'L':
opts.logical = true;
break;
case 'P':
opts.logical = false;
break;
default:
usage();
/* NOTREACHED */
}
}
argc -= optind;
argv += optind;
if (argc != 0)
usage();
/*
* If the logical path is requested and $PWD validates successfully,
* use it. Otherwise (or if -P was given), fall through to the
* physical getcwd(3).
*
* getcwd_physical() allocates via getcwd(NULL,0); we own the memory.
* getcwd_logical() returns a pointer into environ; do not free it.
*/
if (opts.logical && (pwd = getcwd_logical()) != NULL) {
/* pwd points into environ — no free needed */
if (printf("%s\n", pwd) < 0)
goto stdout_err;
} else {
char *phypwd = getcwd_physical();
if (phypwd == NULL) {
fprintf(stderr, "%s: .: %s\n", progname,
strerror(errno));
exit(1);
}
if (printf("%s\n", phypwd) < 0) {
free(phypwd);
goto stdout_err;
}
free(phypwd);
}
if (fflush(stdout) != 0)
goto stdout_err;
return (0);
stdout_err:
fprintf(stderr, "%s: stdout: %s\n", progname, strerror(errno));
exit(1);
}
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