NAME

       perror - print a system error message

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <stdio.h>

       void perror(const char *s);

       #include <errno.h>

       int errno;       /* Not really declared this way; see errno(3) */

       [[deprecated]] const char *const sys_errlist[];
       [[deprecated]] int sys_nerr;

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       sys_errlist, sys_nerr:
           From glibc 2.19 to glibc 2.31:
               _DEFAULT_SOURCE
           glibc 2.19 and earlier:
               _BSD_SOURCE

DESCRIPTION

       The perror() function produces a message on standard error describing the last error encountered during a
       call to a system or library function.

       First (if s is not NULL and *s is not a null byte ('\0')), the argument string s is printed, followed  by
       a colon and a blank.  Then an error message corresponding to the current value of errno and a new-line.

       To be of most use, the argument string should include the name of the function that incurred the error.

       The  global  error  list  sys_errlist[],  which  can be indexed by errno, can be used to obtain the error
       message without the newline.  The largest message number provided in the table is sys_nerr-1.  Be careful
       when  directly  accessing  this  list, because new error values may not have been added to sys_errlist[].
       The use of sys_errlist[] is nowadays deprecated; use strerror(3) instead.

       When a system call fails, it usually returns -1 and sets the variable errno to a  value  describing  what
       went wrong.  (These values can be found in <errno.h>.)  Many library functions do likewise.  The function
       perror() serves to translate this error code into human-readable form.   Note  that  errno  is  undefined
       after  a  successful  system call or library function call: this call may well change this variable, even
       though it succeeds, for example because it internally used  some  other  library  function  that  failed.
       Thus,  if  a failing call is not immediately followed by a call to perror(), the value of errno should be
       saved.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌──────────────────────────────────────────────────────────────────┬───────────────┬─────────────────────┐
       │Interface                                                         │ Attribute     │ Value               │
       ├──────────────────────────────────────────────────────────────────┼───────────────┼─────────────────────┤
       │perror()                                                          │ Thread safety │ MT-Safe race:stderr │
       └──────────────────────────────────────────────────────────────────┴───────────────┴─────────────────────┘

STANDARDS

       errno
       perror()
              C11, POSIX.1-2008.

       sys_nerr
       sys_errlist
              BSD.

HISTORY

       errno
       perror()
              POSIX.1-2001, C89, 4.3BSD.

       sys_nerr
       sys_errlist
              Removed in glibc 2.32.

SEE ALSO

       err(3), errno(3), error(3), strerror(3)