Various pages: Standardize wording around setting of 'errno' on error

In the RETURN VALUE sections, a number of different wordings
are used in to describe the fact that 'errno' is set on error.
There's no reason for the difference in wordings, since the same
thing is being described in each case. Switch to a standard
wording that is the same as FreeBSD and similar to the wording
used in POSIX.1.

In this change, miscellaneous descriptions of the setting
of 'errno' are reworded to the norm of "is set to indicate
the error".

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/getpriority.2

@@ -138,9 +138,9 @@ if \-1 is an error or a legitimate value.
 .PP
 .BR setpriority ()
 returns 0 on success.
-On error, it returns \-1 and sets
+On failure, it returns \-1 and sets
 .I errno
-to indicate the cause of the error.
+to indicate the error.
 .SH ERRORS
 .TP
 .B EINVAL

man2/signal.2

@@ -99,12 +99,12 @@ and
 cannot be caught or ignored.
 .SH RETURN VALUE
 .BR signal ()
-returns the previous value of the signal handler, or
-.B SIG_ERR
-on error.
-In the event of an error,
+returns the previous value of the signal handler
+On failure, it returns
+.BR SIG_ERR ,
+and
 .I errno
-is set to indicate the cause.
+is set to indicate the error.
 .SH ERRORS
 .TP
 .B EINVAL

man2/sigpending.2

@@ -53,10 +53,10 @@ The mask of pending signals is returned in
 .IR set .
 .SH RETURN VALUE
 .BR sigpending ()
-returns 0 on success and \-1 on error.
-In the event of an error,
+returns 0 on success.
+On failure, \-1 is returned and
 .I errno
-is set to indicate the cause.
+is set to indicate the error.
 .SH ERRORS
 .TP
 .B EFAULT

man2/sigprocmask.2

@@ -107,10 +107,10 @@ is unspecified in a multithreaded process; see
 .BR pthread_sigmask (3).
 .SH RETURN VALUE
 .BR sigprocmask ()
-returns 0 on success and \-1 on error.
-In the event of an error,
+returns 0 on success.
+On failure, \-1 is returned and
 .I errno
-is set to indicate the cause.
+is set to indicate the error.
 .SH ERRORS
 .TP
 .B EFAULT

man3/fgetgrent.3

@@ -88,7 +88,7 @@ structure,
 or NULL if there are no more entries or an error occurs.
 In the event of an error,
 .I errno
-is set to indicate the cause.
+is set to indicate the error.
 .SH ERRORS
 .TP
 .B ENOMEM

man3/fgetpwent.3

@@ -92,7 +92,7 @@ structure, or NULL if
 there are no more entries or an error occurs.
 In the event of an error,
 .I errno
-is set to indicate the cause.
+is set to indicate the error.
 .SH ERRORS
 .TP
 .B ENOMEM

man3/fgetwc.3

@@ -52,14 +52,14 @@ There is no reason ever to use it.
 For nonlocking counterparts, see
 .BR unlocked_stdio (3).
 .SH RETURN VALUE
-The
+On success,
 .BR fgetwc ()
-function returns the next wide-character
-from the stream, or
-.BR WEOF .
-In the event of an error,
+returns the next wide-character from the stream.
+Otherwise,
+.B WEOF
+is returned, and
 .I errno
-is set to indicate the cause.
+is set to indicate the error.
 .SH ERRORS
 Apart from the usual ones, there is
 .TP

man3/fputwc.3

@@ -51,14 +51,15 @@ There is no reason ever to use it.
 For nonlocking counterparts, see
 .BR unlocked_stdio (3).
 .SH RETURN VALUE
-The
+On success,
 .BR fputwc ()
-function returns \fIwc\fP if no error occurred, or
+function returns
+.IR wc .
+Otherwise,
 .B WEOF
-to indicate an error.
-In the event of an error,
+is returned, and
 .I errno
-is set to indicate the cause.
+is set to indicate the error.
 .SH ERRORS
 Apart from the usual ones, there is
 .TP

man3/getline.3

@@ -114,9 +114,9 @@ to handle embedded null bytes in the line read.
 .PP
 Both functions return \-1 on failure to read a line (including end-of-file
 condition).
-In the event of an error,
+In the event of a failure,
 .I errno
-is set to indicate the cause.
+is set to indicate the error.
 .SH ERRORS
 .TP
 .B EINVAL

man3/getutent.3

@@ -133,9 +133,9 @@ on failure, it returns NULL.
 .BR utmpname ()
 returns 0 if the new name was successfully stored, or \-1 on failure.
 .PP
-In the event of an error, these functions
+On failure, these functions
 .I errno
-set to indicate the cause.
+set to indicate the error.
 .SH ERRORS
 .TP
 .B ENOMEM

man3/isfdtype.3

@@ -70,9 +70,9 @@ function returns 1 if the file descriptor
 is of type
 .IR fdtype
 and 0 if it is not.
-On error, -1 is returned and
+On failure, \-1 is returned and
 .I errno
-is set to indicate the cause.
+is set to indicate the error.
 .SH ERRORS
 The
 .BR isfdtype ()

man3/malloc_info.3

@@ -48,10 +48,10 @@ must be zero.
 .SH RETURN VALUE
 On success,
 .BR malloc_info ()
-returns 0;
-on error, it returns \-1, with
+returns 0.
+On failure, it returns \-1, and
 .I errno
-set to indicate the cause.
+is set to indicate the error.
 .SH ERRORS
 .TP
 .B EINVAL

man3/putenv.3

@@ -71,11 +71,10 @@ so altering the string changes the environment.
 .SH RETURN VALUE
 The
 .BR putenv ()
-function returns zero on success,
-or nonzero if an error occurs.
-In the event of an error,
+function returns zero on success.
+On failure, it returns a nonzero value, and
 .I errno
-is set to indicate the cause.
+is set to indicate the error.
 .SH ERRORS
 .TP
 .B ENOMEM

man3/putpwent.3

@@ -75,11 +75,10 @@ struct passwd {
 .SH RETURN VALUE
 The
 .BR putpwent ()
-function returns 0 on success, or \-1 if an error
-occurs.
-In the event of an error,
+function returns 0 on success.
+On failure, it returns \-1, and
 .I errno
-is set to indicate the cause.
+is set to indicate the error.
 .SH ERRORS
 .TP
 .B EINVAL

man3/random.3

@@ -129,16 +129,16 @@ function returns no value.
 The
 .BR initstate ()
 function returns a pointer to the previous state array.
-On error,
+On failure, it returns NULL, and
 .I errno
-is set to indicate the cause.
+is set to indicate the error.
 .PP
 On success,
 .BR setstate ()
 returns a pointer to the previous state array.
-On error, it returns NULL, with
+On failure, it returns NULL, and
 .I errno
-set to indicate the error.
+is set to indicate the error.
 .SH ERRORS
 .TP
 .B EINVAL