std/
env.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
//! Inspection and manipulation of the process's environment.
//!
//! This module contains functions to inspect various aspects such as
//! environment variables, process arguments, the current directory, and various
//! other important directories.
//!
//! There are several functions and structs in this module that have a
//! counterpart ending in `os`. Those ending in `os` will return an [`OsString`]
//! and those without will return a [`String`].

#![stable(feature = "env", since = "1.0.0")]

#[cfg(test)]
mod tests;

use crate::error::Error;
use crate::ffi::{OsStr, OsString};
use crate::path::{Path, PathBuf};
use crate::sys::os as os_imp;
use crate::{fmt, io, sys};

/// Returns the current working directory as a [`PathBuf`].
///
/// # Platform-specific behavior
///
/// This function [currently] corresponds to the `getcwd` function on Unix
/// and the `GetCurrentDirectoryW` function on Windows.
///
/// [currently]: crate::io#platform-specific-behavior
///
/// # Errors
///
/// Returns an [`Err`] if the current working directory value is invalid.
/// Possible cases:
///
/// * Current directory does not exist.
/// * There are insufficient permissions to access the current directory.
///
/// # Examples
///
/// ```
/// use std::env;
///
/// fn main() -> std::io::Result<()> {
///     let path = env::current_dir()?;
///     println!("The current directory is {}", path.display());
///     Ok(())
/// }
/// ```
#[doc(alias = "pwd")]
#[doc(alias = "getcwd")]
#[doc(alias = "GetCurrentDirectory")]
#[stable(feature = "env", since = "1.0.0")]
pub fn current_dir() -> io::Result<PathBuf> {
    os_imp::getcwd()
}

/// Changes the current working directory to the specified path.
///
/// # Platform-specific behavior
///
/// This function [currently] corresponds to the `chdir` function on Unix
/// and the `SetCurrentDirectoryW` function on Windows.
///
/// Returns an [`Err`] if the operation fails.
///
/// [currently]: crate::io#platform-specific-behavior
///
/// # Examples
///
/// ```
/// use std::env;
/// use std::path::Path;
///
/// let root = Path::new("/");
/// assert!(env::set_current_dir(&root).is_ok());
/// println!("Successfully changed working directory to {}!", root.display());
/// ```
#[doc(alias = "chdir", alias = "SetCurrentDirectory", alias = "SetCurrentDirectoryW")]
#[stable(feature = "env", since = "1.0.0")]
pub fn set_current_dir<P: AsRef<Path>>(path: P) -> io::Result<()> {
    os_imp::chdir(path.as_ref())
}

/// An iterator over a snapshot of the environment variables of this process.
///
/// This structure is created by [`env::vars()`]. See its documentation for more.
///
/// [`env::vars()`]: vars
#[stable(feature = "env", since = "1.0.0")]
pub struct Vars {
    inner: VarsOs,
}

/// An iterator over a snapshot of the environment variables of this process.
///
/// This structure is created by [`env::vars_os()`]. See its documentation for more.
///
/// [`env::vars_os()`]: vars_os
#[stable(feature = "env", since = "1.0.0")]
pub struct VarsOs {
    inner: os_imp::Env,
}

/// Returns an iterator of (variable, value) pairs of strings, for all the
/// environment variables of the current process.
///
/// The returned iterator contains a snapshot of the process's environment
/// variables at the time of this invocation. Modifications to environment
/// variables afterwards will not be reflected in the returned iterator.
///
/// # Panics
///
/// While iterating, the returned iterator will panic if any key or value in the
/// environment is not valid unicode. If this is not desired, consider using
/// [`env::vars_os()`].
///
/// # Examples
///
/// ```
/// // Print all environment variables.
/// for (key, value) in std::env::vars() {
///     println!("{key}: {value}");
/// }
/// ```
///
/// [`env::vars_os()`]: vars_os
#[must_use]
#[stable(feature = "env", since = "1.0.0")]
pub fn vars() -> Vars {
    Vars { inner: vars_os() }
}

/// Returns an iterator of (variable, value) pairs of OS strings, for all the
/// environment variables of the current process.
///
/// The returned iterator contains a snapshot of the process's environment
/// variables at the time of this invocation. Modifications to environment
/// variables afterwards will not be reflected in the returned iterator.
///
/// Note that the returned iterator will not check if the environment variables
/// are valid Unicode. If you want to panic on invalid UTF-8,
/// use the [`vars`] function instead.
///
/// # Examples
///
/// ```
/// // Print all environment variables.
/// for (key, value) in std::env::vars_os() {
///     println!("{key:?}: {value:?}");
/// }
/// ```
#[must_use]
#[stable(feature = "env", since = "1.0.0")]
pub fn vars_os() -> VarsOs {
    VarsOs { inner: os_imp::env() }
}

#[stable(feature = "env", since = "1.0.0")]
impl Iterator for Vars {
    type Item = (String, String);
    fn next(&mut self) -> Option<(String, String)> {
        self.inner.next().map(|(a, b)| (a.into_string().unwrap(), b.into_string().unwrap()))
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.inner.size_hint()
    }
}

#[stable(feature = "std_debug", since = "1.16.0")]
impl fmt::Debug for Vars {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let Self { inner: VarsOs { inner } } = self;
        f.debug_struct("Vars").field("inner", &inner.str_debug()).finish()
    }
}

#[stable(feature = "env", since = "1.0.0")]
impl Iterator for VarsOs {
    type Item = (OsString, OsString);
    fn next(&mut self) -> Option<(OsString, OsString)> {
        self.inner.next()
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.inner.size_hint()
    }
}

#[stable(feature = "std_debug", since = "1.16.0")]
impl fmt::Debug for VarsOs {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let Self { inner } = self;
        f.debug_struct("VarsOs").field("inner", inner).finish()
    }
}

/// Fetches the environment variable `key` from the current process.
///
/// # Errors
///
/// Returns [`VarError::NotPresent`] if:
/// - The variable is not set.
/// - The variable's name contains an equal sign or NUL (`'='` or `'\0'`).
///
/// Returns [`VarError::NotUnicode`] if the variable's value is not valid
/// Unicode. If this is not desired, consider using [`var_os`].
///
/// # Examples
///
/// ```
/// use std::env;
///
/// let key = "HOME";
/// match env::var(key) {
///     Ok(val) => println!("{key}: {val:?}"),
///     Err(e) => println!("couldn't interpret {key}: {e}"),
/// }
/// ```
#[stable(feature = "env", since = "1.0.0")]
pub fn var<K: AsRef<OsStr>>(key: K) -> Result<String, VarError> {
    _var(key.as_ref())
}

fn _var(key: &OsStr) -> Result<String, VarError> {
    match var_os(key) {
        Some(s) => s.into_string().map_err(VarError::NotUnicode),
        None => Err(VarError::NotPresent),
    }
}

/// Fetches the environment variable `key` from the current process, returning
/// [`None`] if the variable isn't set or if there is another error.
///
/// It may return `None` if the environment variable's name contains
/// the equal sign character (`=`) or the NUL character.
///
/// Note that this function will not check if the environment variable
/// is valid Unicode. If you want to have an error on invalid UTF-8,
/// use the [`var`] function instead.
///
/// # Examples
///
/// ```
/// use std::env;
///
/// let key = "HOME";
/// match env::var_os(key) {
///     Some(val) => println!("{key}: {val:?}"),
///     None => println!("{key} is not defined in the environment.")
/// }
/// ```
///
/// If expecting a delimited variable (such as `PATH`), [`split_paths`]
/// can be used to separate items.
#[must_use]
#[stable(feature = "env", since = "1.0.0")]
pub fn var_os<K: AsRef<OsStr>>(key: K) -> Option<OsString> {
    _var_os(key.as_ref())
}

fn _var_os(key: &OsStr) -> Option<OsString> {
    os_imp::getenv(key)
}

/// The error type for operations interacting with environment variables.
/// Possibly returned from [`env::var()`].
///
/// [`env::var()`]: var
#[derive(Debug, PartialEq, Eq, Clone)]
#[stable(feature = "env", since = "1.0.0")]
pub enum VarError {
    /// The specified environment variable was not present in the current
    /// process's environment.
    #[stable(feature = "env", since = "1.0.0")]
    NotPresent,

    /// The specified environment variable was found, but it did not contain
    /// valid unicode data. The found data is returned as a payload of this
    /// variant.
    #[stable(feature = "env", since = "1.0.0")]
    NotUnicode(#[stable(feature = "env", since = "1.0.0")] OsString),
}

#[stable(feature = "env", since = "1.0.0")]
impl fmt::Display for VarError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            VarError::NotPresent => write!(f, "environment variable not found"),
            VarError::NotUnicode(ref s) => {
                write!(f, "environment variable was not valid unicode: {:?}", s)
            }
        }
    }
}

#[stable(feature = "env", since = "1.0.0")]
impl Error for VarError {
    #[allow(deprecated)]
    fn description(&self) -> &str {
        match *self {
            VarError::NotPresent => "environment variable not found",
            VarError::NotUnicode(..) => "environment variable was not valid unicode",
        }
    }
}

/// Sets the environment variable `key` to the value `value` for the currently running
/// process.
///
/// # Safety
///
/// This function is safe to call in a single-threaded program.
///
/// This function is also always safe to call on Windows, in single-threaded
/// and multi-threaded programs.
///
/// In multi-threaded programs on other operating systems, the only safe option is
/// to not use `set_var` or `remove_var` at all.
///
/// The exact requirement is: you
/// must ensure that there are no other threads concurrently writing or
/// *reading*(!) the environment through functions or global variables other
/// than the ones in this module. The problem is that these operating systems
/// do not provide a thread-safe way to read the environment, and most C
/// libraries, including libc itself, do not advertise which functions read
/// from the environment. Even functions from the Rust standard library may
/// read the environment without going through this module, e.g. for DNS
/// lookups from [`std::net::ToSocketAddrs`]. No stable guarantee is made about
/// which functions may read from the environment in future versions of a
/// library. All this makes it not practically possible for you to guarantee
/// that no other thread will read the environment, so the only safe option is
/// to not use `set_var` or `remove_var` in multi-threaded programs at all.
///
/// Discussion of this unsafety on Unix may be found in:
///
///  - [Austin Group Bugzilla](https://austingroupbugs.net/view.php?id=188)
///  - [GNU C library Bugzilla](https://sourceware.org/bugzilla/show_bug.cgi?id=15607#c2)
///
/// [`std::net::ToSocketAddrs`]: crate::net::ToSocketAddrs
///
/// # Panics
///
/// This function may panic if `key` is empty, contains an ASCII equals sign `'='`
/// or the NUL character `'\0'`, or when `value` contains the NUL character.
///
/// # Examples
///
/// ```
/// use std::env;
///
/// let key = "KEY";
/// unsafe {
///     env::set_var(key, "VALUE");
/// }
/// assert_eq!(env::var(key), Ok("VALUE".to_string()));
/// ```
#[rustc_deprecated_safe_2024(
    audit_that = "the environment access only happens in single-threaded code"
)]
#[stable(feature = "env", since = "1.0.0")]
pub unsafe fn set_var<K: AsRef<OsStr>, V: AsRef<OsStr>>(key: K, value: V) {
    let (key, value) = (key.as_ref(), value.as_ref());
    unsafe { os_imp::setenv(key, value) }.unwrap_or_else(|e| {
        panic!("failed to set environment variable `{key:?}` to `{value:?}`: {e}")
    })
}

/// Removes an environment variable from the environment of the currently running process.
///
/// # Safety
///
/// This function is safe to call in a single-threaded program.
///
/// This function is also always safe to call on Windows, in single-threaded
/// and multi-threaded programs.
///
/// In multi-threaded programs on other operating systems, the only safe option is
/// to not use `set_var` or `remove_var` at all.
///
/// The exact requirement is: you
/// must ensure that there are no other threads concurrently writing or
/// *reading*(!) the environment through functions or global variables other
/// than the ones in this module. The problem is that these operating systems
/// do not provide a thread-safe way to read the environment, and most C
/// libraries, including libc itself, do not advertise which functions read
/// from the environment. Even functions from the Rust standard library may
/// read the environment without going through this module, e.g. for DNS
/// lookups from [`std::net::ToSocketAddrs`]. No stable guarantee is made about
/// which functions may read from the environment in future versions of a
/// library. All this makes it not practically possible for you to guarantee
/// that no other thread will read the environment, so the only safe option is
/// to not use `set_var` or `remove_var` in multi-threaded programs at all.
///
/// Discussion of this unsafety on Unix may be found in:
///
///  - [Austin Group Bugzilla](https://austingroupbugs.net/view.php?id=188)
///  - [GNU C library Bugzilla](https://sourceware.org/bugzilla/show_bug.cgi?id=15607#c2)
///
/// [`std::net::ToSocketAddrs`]: crate::net::ToSocketAddrs
///
/// # Panics
///
/// This function may panic if `key` is empty, contains an ASCII equals sign
/// `'='` or the NUL character `'\0'`, or when the value contains the NUL
/// character.
///
/// # Examples
///
/// ```no_run
/// use std::env;
///
/// let key = "KEY";
/// unsafe {
///     env::set_var(key, "VALUE");
/// }
/// assert_eq!(env::var(key), Ok("VALUE".to_string()));
///
/// unsafe {
///     env::remove_var(key);
/// }
/// assert!(env::var(key).is_err());
/// ```
#[rustc_deprecated_safe_2024(
    audit_that = "the environment access only happens in single-threaded code"
)]
#[stable(feature = "env", since = "1.0.0")]
pub unsafe fn remove_var<K: AsRef<OsStr>>(key: K) {
    let key = key.as_ref();
    unsafe { os_imp::unsetenv(key) }
        .unwrap_or_else(|e| panic!("failed to remove environment variable `{key:?}`: {e}"))
}

/// An iterator that splits an environment variable into paths according to
/// platform-specific conventions.
///
/// The iterator element type is [`PathBuf`].
///
/// This structure is created by [`env::split_paths()`]. See its
/// documentation for more.
///
/// [`env::split_paths()`]: split_paths
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "env", since = "1.0.0")]
pub struct SplitPaths<'a> {
    inner: os_imp::SplitPaths<'a>,
}

/// Parses input according to platform conventions for the `PATH`
/// environment variable.
///
/// Returns an iterator over the paths contained in `unparsed`. The iterator
/// element type is [`PathBuf`].
///
/// On most Unix platforms, the separator is `:` and on Windows it is `;`. This
/// also performs unquoting on Windows.
///
/// [`join_paths`] can be used to recombine elements.
///
/// # Panics
///
/// This will panic on systems where there is no delimited `PATH` variable,
/// such as UEFI.
///
/// # Examples
///
/// ```
/// use std::env;
///
/// let key = "PATH";
/// match env::var_os(key) {
///     Some(paths) => {
///         for path in env::split_paths(&paths) {
///             println!("'{}'", path.display());
///         }
///     }
///     None => println!("{key} is not defined in the environment.")
/// }
/// ```
#[stable(feature = "env", since = "1.0.0")]
pub fn split_paths<T: AsRef<OsStr> + ?Sized>(unparsed: &T) -> SplitPaths<'_> {
    SplitPaths { inner: os_imp::split_paths(unparsed.as_ref()) }
}

#[stable(feature = "env", since = "1.0.0")]
impl<'a> Iterator for SplitPaths<'a> {
    type Item = PathBuf;
    fn next(&mut self) -> Option<PathBuf> {
        self.inner.next()
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.inner.size_hint()
    }
}

#[stable(feature = "std_debug", since = "1.16.0")]
impl fmt::Debug for SplitPaths<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("SplitPaths").finish_non_exhaustive()
    }
}

/// The error type for operations on the `PATH` variable. Possibly returned from
/// [`env::join_paths()`].
///
/// [`env::join_paths()`]: join_paths
#[derive(Debug)]
#[stable(feature = "env", since = "1.0.0")]
pub struct JoinPathsError {
    inner: os_imp::JoinPathsError,
}

/// Joins a collection of [`Path`]s appropriately for the `PATH`
/// environment variable.
///
/// # Errors
///
/// Returns an [`Err`] (containing an error message) if one of the input
/// [`Path`]s contains an invalid character for constructing the `PATH`
/// variable (a double quote on Windows or a colon on Unix), or if the system
/// does not have a `PATH`-like variable (e.g. UEFI or WASI).
///
/// # Examples
///
/// Joining paths on a Unix-like platform:
///
/// ```
/// use std::env;
/// use std::ffi::OsString;
/// use std::path::Path;
///
/// fn main() -> Result<(), env::JoinPathsError> {
/// # if cfg!(unix) {
///     let paths = [Path::new("/bin"), Path::new("/usr/bin")];
///     let path_os_string = env::join_paths(paths.iter())?;
///     assert_eq!(path_os_string, OsString::from("/bin:/usr/bin"));
/// # }
///     Ok(())
/// }
/// ```
///
/// Joining a path containing a colon on a Unix-like platform results in an
/// error:
///
/// ```
/// # if cfg!(unix) {
/// use std::env;
/// use std::path::Path;
///
/// let paths = [Path::new("/bin"), Path::new("/usr/bi:n")];
/// assert!(env::join_paths(paths.iter()).is_err());
/// # }
/// ```
///
/// Using `env::join_paths()` with [`env::split_paths()`] to append an item to
/// the `PATH` environment variable:
///
/// ```
/// use std::env;
/// use std::path::PathBuf;
///
/// fn main() -> Result<(), env::JoinPathsError> {
///     if let Some(path) = env::var_os("PATH") {
///         let mut paths = env::split_paths(&path).collect::<Vec<_>>();
///         paths.push(PathBuf::from("/home/xyz/bin"));
///         let new_path = env::join_paths(paths)?;
///         env::set_var("PATH", &new_path);
///     }
///
///     Ok(())
/// }
/// ```
///
/// [`env::split_paths()`]: split_paths
#[stable(feature = "env", since = "1.0.0")]
pub fn join_paths<I, T>(paths: I) -> Result<OsString, JoinPathsError>
where
    I: IntoIterator<Item = T>,
    T: AsRef<OsStr>,
{
    os_imp::join_paths(paths.into_iter()).map_err(|e| JoinPathsError { inner: e })
}

#[stable(feature = "env", since = "1.0.0")]
impl fmt::Display for JoinPathsError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.inner.fmt(f)
    }
}

#[stable(feature = "env", since = "1.0.0")]
impl Error for JoinPathsError {
    #[allow(deprecated, deprecated_in_future)]
    fn description(&self) -> &str {
        self.inner.description()
    }
}

/// Returns the path of the current user's home directory if known.
///
/// # Unix
///
/// - Returns the value of the 'HOME' environment variable if it is set
///   (including to an empty string).
/// - Otherwise, it tries to determine the home directory by invoking the `getpwuid_r` function
///   using the UID of the current user. An empty home directory field returned from the
///   `getpwuid_r` function is considered to be a valid value.
/// - Returns `None` if the current user has no entry in the /etc/passwd file.
///
/// # Windows
///
/// - Returns the value of the 'HOME' environment variable if it is set
///   (including to an empty string).
/// - Otherwise, returns the value of the 'USERPROFILE' environment variable if it is set
///   (including to an empty string).
/// - If both do not exist, [`GetUserProfileDirectory`][msdn] is used to return the path.
///
/// [msdn]: https://docs.microsoft.com/en-us/windows/win32/api/userenv/nf-userenv-getuserprofiledirectorya
///
/// # Deprecation
///
/// This function is deprecated because the behaviour on Windows is not correct.
/// The 'HOME' environment variable is not standard on Windows, and may not produce
/// desired results; for instance, under Cygwin or Mingw it will return `/home/you`
/// when it should return `C:\Users\you`.
///
/// # Examples
///
/// ```
/// use std::env;
///
/// match env::home_dir() {
///     Some(path) => println!("Your home directory, probably: {}", path.display()),
///     None => println!("Impossible to get your home dir!"),
/// }
/// ```
#[deprecated(
    since = "1.29.0",
    note = "This function's behavior may be unexpected on Windows. \
            Consider using a crate from crates.io instead."
)]
#[must_use]
#[stable(feature = "env", since = "1.0.0")]
pub fn home_dir() -> Option<PathBuf> {
    os_imp::home_dir()
}

/// Returns the path of a temporary directory.
///
/// The temporary directory may be shared among users, or between processes
/// with different privileges; thus, the creation of any files or directories
/// in the temporary directory must use a secure method to create a uniquely
/// named file. Creating a file or directory with a fixed or predictable name
/// may result in "insecure temporary file" security vulnerabilities. Consider
/// using a crate that securely creates temporary files or directories.
///
/// # Platform-specific behavior
///
/// On Unix, returns the value of the `TMPDIR` environment variable if it is
/// set, otherwise for non-Android it returns `/tmp`. On Android, since there
/// is no global temporary folder (it is usually allocated per-app), it returns
/// `/data/local/tmp`.
/// On Windows, the behavior is equivalent to that of [`GetTempPath2`][GetTempPath2] /
/// [`GetTempPath`][GetTempPath], which this function uses internally.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
/// [GetTempPath2]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettemppath2a
/// [GetTempPath]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettemppatha
///
/// ```no_run
/// use std::env;
///
/// fn main() {
///     let dir = env::temp_dir();
///     println!("Temporary directory: {}", dir.display());
/// }
/// ```
#[must_use]
#[doc(alias = "GetTempPath", alias = "GetTempPath2")]
#[stable(feature = "env", since = "1.0.0")]
pub fn temp_dir() -> PathBuf {
    os_imp::temp_dir()
}

/// Returns the full filesystem path of the current running executable.
///
/// # Platform-specific behavior
///
/// If the executable was invoked through a symbolic link, some platforms will
/// return the path of the symbolic link and other platforms will return the
/// path of the symbolic link’s target.
///
/// If the executable is renamed while it is running, platforms may return the
/// path at the time it was loaded instead of the new path.
///
/// # Errors
///
/// Acquiring the path of the current executable is a platform-specific operation
/// that can fail for a good number of reasons. Some errors can include, but not
/// be limited to, filesystem operations failing or general syscall failures.
///
/// # Security
///
/// The output of this function should not be trusted for anything
/// that might have security implications. Basically, if users can run
/// the executable, they can change the output arbitrarily.
///
/// As an example, you can easily introduce a race condition. It goes
/// like this:
///
/// 1. You get the path to the current executable using `current_exe()`, and
///    store it in a variable.
/// 2. Time passes. A malicious actor removes the current executable, and
///    replaces it with a malicious one.
/// 3. You then use the stored path to re-execute the current
///    executable.
///
/// You expected to safely execute the current executable, but you're
/// instead executing something completely different. The code you
/// just executed run with your privileges.
///
/// This sort of behavior has been known to [lead to privilege escalation] when
/// used incorrectly.
///
/// [lead to privilege escalation]: https://securityvulns.com/Wdocument183.html
///
/// # Examples
///
/// ```
/// use std::env;
///
/// match env::current_exe() {
///     Ok(exe_path) => println!("Path of this executable is: {}",
///                              exe_path.display()),
///     Err(e) => println!("failed to get current exe path: {e}"),
/// };
/// ```
#[stable(feature = "env", since = "1.0.0")]
pub fn current_exe() -> io::Result<PathBuf> {
    os_imp::current_exe()
}

/// An iterator over the arguments of a process, yielding a [`String`] value for
/// each argument.
///
/// This struct is created by [`env::args()`]. See its documentation
/// for more.
///
/// The first element is traditionally the path of the executable, but it can be
/// set to arbitrary text, and might not even exist. This means this property
/// should not be relied upon for security purposes.
///
/// [`env::args()`]: args
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "env", since = "1.0.0")]
pub struct Args {
    inner: ArgsOs,
}

/// An iterator over the arguments of a process, yielding an [`OsString`] value
/// for each argument.
///
/// This struct is created by [`env::args_os()`]. See its documentation
/// for more.
///
/// The first element is traditionally the path of the executable, but it can be
/// set to arbitrary text, and might not even exist. This means this property
/// should not be relied upon for security purposes.
///
/// [`env::args_os()`]: args_os
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "env", since = "1.0.0")]
pub struct ArgsOs {
    inner: sys::args::Args,
}

/// Returns the arguments that this program was started with (normally passed
/// via the command line).
///
/// The first element is traditionally the path of the executable, but it can be
/// set to arbitrary text, and might not even exist. This means this property should
/// not be relied upon for security purposes.
///
/// On Unix systems the shell usually expands unquoted arguments with glob patterns
/// (such as `*` and `?`). On Windows this is not done, and such arguments are
/// passed as-is.
///
/// On glibc Linux systems, arguments are retrieved by placing a function in `.init_array`.
/// glibc passes `argc`, `argv`, and `envp` to functions in `.init_array`, as a non-standard
/// extension. This allows `std::env::args` to work even in a `cdylib` or `staticlib`, as it
/// does on macOS and Windows.
///
/// # Panics
///
/// The returned iterator will panic during iteration if any argument to the
/// process is not valid Unicode. If this is not desired,
/// use the [`args_os`] function instead.
///
/// # Examples
///
/// ```
/// use std::env;
///
/// // Prints each argument on a separate line
/// for argument in env::args() {
///     println!("{argument}");
/// }
/// ```
#[stable(feature = "env", since = "1.0.0")]
pub fn args() -> Args {
    Args { inner: args_os() }
}

/// Returns the arguments that this program was started with (normally passed
/// via the command line).
///
/// The first element is traditionally the path of the executable, but it can be
/// set to arbitrary text, and might not even exist. This means this property should
/// not be relied upon for security purposes.
///
/// On Unix systems the shell usually expands unquoted arguments with glob patterns
/// (such as `*` and `?`). On Windows this is not done, and such arguments are
/// passed as-is.
///
/// On glibc Linux systems, arguments are retrieved by placing a function in `.init_array`.
/// glibc passes `argc`, `argv`, and `envp` to functions in `.init_array`, as a non-standard
/// extension. This allows `std::env::args_os` to work even in a `cdylib` or `staticlib`, as it
/// does on macOS and Windows.
///
/// Note that the returned iterator will not check if the arguments to the
/// process are valid Unicode. If you want to panic on invalid UTF-8,
/// use the [`args`] function instead.
///
/// # Examples
///
/// ```
/// use std::env;
///
/// // Prints each argument on a separate line
/// for argument in env::args_os() {
///     println!("{argument:?}");
/// }
/// ```
#[stable(feature = "env", since = "1.0.0")]
pub fn args_os() -> ArgsOs {
    ArgsOs { inner: sys::args::args() }
}

#[stable(feature = "env_unimpl_send_sync", since = "1.26.0")]
impl !Send for Args {}

#[stable(feature = "env_unimpl_send_sync", since = "1.26.0")]
impl !Sync for Args {}

#[stable(feature = "env", since = "1.0.0")]
impl Iterator for Args {
    type Item = String;
    fn next(&mut self) -> Option<String> {
        self.inner.next().map(|s| s.into_string().unwrap())
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.inner.size_hint()
    }
}

#[stable(feature = "env", since = "1.0.0")]
impl ExactSizeIterator for Args {
    fn len(&self) -> usize {
        self.inner.len()
    }
    fn is_empty(&self) -> bool {
        self.inner.is_empty()
    }
}

#[stable(feature = "env_iterators", since = "1.12.0")]
impl DoubleEndedIterator for Args {
    fn next_back(&mut self) -> Option<String> {
        self.inner.next_back().map(|s| s.into_string().unwrap())
    }
}

#[stable(feature = "std_debug", since = "1.16.0")]
impl fmt::Debug for Args {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let Self { inner: ArgsOs { inner } } = self;
        f.debug_struct("Args").field("inner", inner).finish()
    }
}

#[stable(feature = "env_unimpl_send_sync", since = "1.26.0")]
impl !Send for ArgsOs {}

#[stable(feature = "env_unimpl_send_sync", since = "1.26.0")]
impl !Sync for ArgsOs {}

#[stable(feature = "env", since = "1.0.0")]
impl Iterator for ArgsOs {
    type Item = OsString;
    fn next(&mut self) -> Option<OsString> {
        self.inner.next()
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.inner.size_hint()
    }
}

#[stable(feature = "env", since = "1.0.0")]
impl ExactSizeIterator for ArgsOs {
    fn len(&self) -> usize {
        self.inner.len()
    }
    fn is_empty(&self) -> bool {
        self.inner.is_empty()
    }
}

#[stable(feature = "env_iterators", since = "1.12.0")]
impl DoubleEndedIterator for ArgsOs {
    fn next_back(&mut self) -> Option<OsString> {
        self.inner.next_back()
    }
}

#[stable(feature = "std_debug", since = "1.16.0")]
impl fmt::Debug for ArgsOs {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let Self { inner } = self;
        f.debug_struct("ArgsOs").field("inner", inner).finish()
    }
}

/// Constants associated with the current target
#[stable(feature = "env", since = "1.0.0")]
pub mod consts {
    use crate::sys::env::os;

    /// A string describing the architecture of the CPU that is currently in use.
    /// An example value may be: `"x86"`, `"arm"` or `"riscv64"`.
    ///
    /// <details><summary>Full list of possible values</summary>
    ///
    /// * `"x86"`
    /// * `"x86_64"`
    /// * `"arm"`
    /// * `"aarch64"`
    /// * `"m68k"`
    /// * `"mips"`
    /// * `"mips32r6"`
    /// * `"mips64"`
    /// * `"mips64r6"`
    /// * `"csky"`
    /// * `"powerpc"`
    /// * `"powerpc64"`
    /// * `"riscv32"`
    /// * `"riscv64"`
    /// * `"s390x"`
    /// * `"sparc"`
    /// * `"sparc64"`
    /// * `"hexagon"`
    /// * `"loongarch64"`
    ///
    /// </details>
    #[stable(feature = "env", since = "1.0.0")]
    pub const ARCH: &str = env!("STD_ENV_ARCH");

    /// A string describing the family of the operating system.
    /// An example value may be: `"unix"`, or `"windows"`.
    ///
    /// This value may be an empty string if the family is unknown.
    ///
    /// <details><summary>Full list of possible values</summary>
    ///
    /// * `"unix"`
    /// * `"windows"`
    /// * `"itron"`
    /// * `"wasm"`
    /// * `""`
    ///
    /// </details>
    #[stable(feature = "env", since = "1.0.0")]
    pub const FAMILY: &str = os::FAMILY;

    /// A string describing the specific operating system in use.
    /// An example value may be: `"linux"`, or `"freebsd"`.
    ///
    /// <details><summary>Full list of possible values</summary>
    ///
    /// * `"linux"`
    /// * `"windows"`
    /// * `"macos"`
    /// * `"android"`
    /// * `"ios"`
    /// * `"openbsd"`
    /// * `"freebsd"`
    /// * `"netbsd"`
    /// * `"wasi"`
    /// * `"hermit"`
    /// * `"aix"`
    /// * `"apple"`
    /// * `"dragonfly"`
    /// * `"emscripten"`
    /// * `"espidf"`
    /// * `"fortanix"`
    /// * `"uefi"`
    /// * `"fuchsia"`
    /// * `"haiku"`
    /// * `"hermit"`
    /// * `"watchos"`
    /// * `"visionos"`
    /// * `"tvos"`
    /// * `"horizon"`
    /// * `"hurd"`
    /// * `"illumos"`
    /// * `"l4re"`
    /// * `"nto"`
    /// * `"redox"`
    /// * `"solaris"`
    /// * `"solid_asp3`
    /// * `"vita"`
    /// * `"vxworks"`
    /// * `"xous"`
    ///
    /// </details>
    #[stable(feature = "env", since = "1.0.0")]
    pub const OS: &str = os::OS;

    /// Specifies the filename prefix, if any, used for shared libraries on this platform.
    /// This is either `"lib"` or an empty string. (`""`).
    #[stable(feature = "env", since = "1.0.0")]
    pub const DLL_PREFIX: &str = os::DLL_PREFIX;

    /// Specifies the filename suffix, if any, used for shared libraries on this platform.
    /// An example value may be: `".so"`, `".elf"`, or `".dll"`.
    ///
    /// The possible values are identical to those of [`DLL_EXTENSION`], but with the leading period included.
    #[stable(feature = "env", since = "1.0.0")]
    pub const DLL_SUFFIX: &str = os::DLL_SUFFIX;

    /// Specifies the file extension, if any, used for shared libraries on this platform that goes after the dot.
    /// An example value may be: `"so"`, `"elf"`, or `"dll"`.
    ///
    /// <details><summary>Full list of possible values</summary>
    ///
    /// * `"so"`
    /// * `"dylib"`
    /// * `"dll"`
    /// * `"sgxs"`
    /// * `"a"`
    /// * `"elf"`
    /// * `"wasm"`
    /// * `""` (an empty string)
    ///
    /// </details>
    #[stable(feature = "env", since = "1.0.0")]
    pub const DLL_EXTENSION: &str = os::DLL_EXTENSION;

    /// Specifies the filename suffix, if any, used for executable binaries on this platform.
    /// An example value may be: `".exe"`, or `".efi"`.
    ///
    /// The possible values are identical to those of [`EXE_EXTENSION`], but with the leading period included.
    #[stable(feature = "env", since = "1.0.0")]
    pub const EXE_SUFFIX: &str = os::EXE_SUFFIX;

    /// Specifies the file extension, if any, used for executable binaries on this platform.
    /// An example value may be: `"exe"`, or an empty string (`""`).
    ///
    /// <details><summary>Full list of possible values</summary>
    ///
    /// * `"exe"`
    /// * `"efi"`
    /// * `"js"`
    /// * `"sgxs"`
    /// * `"elf"`
    /// * `"wasm"`
    /// * `""` (an empty string)
    ///
    /// </details>
    #[stable(feature = "env", since = "1.0.0")]
    pub const EXE_EXTENSION: &str = os::EXE_EXTENSION;
}