mirror of https://github.com/mkerrisk/man-pages
167 lines
4.2 KiB
Groff
167 lines
4.2 KiB
Groff
.\" Copyright (c) 1999 Andries Brouwer (aeb@cwi.nl)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH TEMPNAM 3 2007-07-26 "" "Linux Programmer's Manual"
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.SH NAME
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tempnam \- create a name for a temporary file
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.SH SYNOPSIS
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.nf
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.B #include <stdio.h>
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.sp
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.BI "char *tempnam(const char *" dir ", const char *" pfx );
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.fi
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.BR tempnam ():
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_BSD_SOURCE || _SVID_SOURCE
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.SH DESCRIPTION
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The
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.BR tempnam ()
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function returns a pointer to a string that is a valid filename,
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and such that a file with this name did not exist when
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.BR tempnam ()
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checked.
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The filename suffix of the pathname generated will start with
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.I pfx
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in case
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.I pfx
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is a non-NULL string of at most five bytes.
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The directory prefix part of the pathname generated is required to
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be "appropriate" (often that at least implies writable).
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Attempts to find an appropriate directory go through the following
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steps:
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.TP 3
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a)
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In case the environment variable
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.B TMPDIR
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exists and
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contains the name of an appropriate directory, that is used.
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.TP
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b)
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Otherwise, if the
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.I dir
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argument is non-NULL and appropriate, it is used.
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.TP
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c)
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Otherwise,
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.I P_tmpdir
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(as defined in
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.IR <stdio.h> )
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is used when appropriate.
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.TP
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d)
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Finally an implementation-defined directory may be used.
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.PP
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The string returned by
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.BR tempnam ()
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is allocated using
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.BR malloc (3)
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and hence should be freed by
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.BR free (3).
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.SH "RETURN VALUE"
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The
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.BR tempnam ()
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function returns a pointer to a unique temporary
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filename, or NULL if a unique name cannot be generated.
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.SH ERRORS
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.TP
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.B ENOMEM
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Allocation of storage failed.
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.SH "CONFORMING TO"
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SVr4, 4.3BSD, POSIX.1-2001
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.\" FIXME . Mar 08: The next POSIX.1 revisions marks tempnam() obsolete.
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.SH NOTES
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Although
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.BR tempnam ()
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generates names that are difficult to guess,
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it is nevertheless possible that between the time that
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.BR tempnam ()
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returns a pathname, and the time that the program opens it,
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another program might create that pathname using
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.BR open (2),
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or create it as a symbolic link.
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This can lead to security holes.
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To avoid such possibilities, use the
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.BR open (2)
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.B O_EXCL
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flag to open the pathname.
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Or better yet, use
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.BR mkstemp (3)
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or
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.BR tmpfile (3).
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SUSv2 does not mention the use of
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.BR TMPDIR ;
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glibc will use it only
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when the program is not set-user-ID.
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On SVr4, the directory used under \fBd)\fP is
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.I /tmp
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(and this is what glibc does).
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.LP
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Because it dynamically allocates memory used to return the pathname,
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.BR tempnam ()
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is reentrant, and thus thread safe, unlike
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.BR tmpnam (3).
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.LP
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The
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.BR tempnam ()
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function generates a different string each time it is called,
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up to
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.B TMP_MAX
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(defined in
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.IR <stdio.h> )
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times.
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If it is called more than
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.B TMP_MAX
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times,
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the behavior is implementation defined.
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.LP
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.BR tempnam ()
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uses at most the first five bytes from
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.IR pfx .
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The glibc implementation of
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.BR tempnam ()
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will fail with the error
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.B EEXIST
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upon failure to find a unique name.
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.SH BUGS
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The precise meaning of "appropriate" is undefined;
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it is unspecified how accessibility of a directory is determined.
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Never use this function.
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Use
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.BR mkstemp (3)
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or
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.BR tmpfile (3)
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instead.
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.SH "SEE ALSO"
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.BR mkstemp (3),
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.BR mktemp (3),
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.BR tmpfile (3),
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.BR tmpnam (3)
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