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| ID | Category | Severity | Type | Date Submitted | Last Update | |||||||
| 0001616 | [Issue 8 drafts] Shell and Utilities | Editorial | Enhancement Request | 2022-11-08 23:03 | 2022-11-09 13:18 | |||||||
| Reporter | illiliti | View Status | public | |||||||||
| Assigned To | ||||||||||||
| Priority | normal | Resolution | Open | |||||||||
| Status | New | Product Version | Draft 2.1 | |||||||||
| Name | Mark Lundblad | |||||||||||
| Organization | ||||||||||||
| User Reference | ||||||||||||
| Section | Shell and Utilities | |||||||||||
| Page Number | - | |||||||||||
| Line Number | - | |||||||||||
| Final Accepted Text | ||||||||||||
| Summary | 0001616: Standardize mktemp utility | |||||||||||
| Description |
The current standard has no reliable and convenient utility to create temporary file or directory, despite that low-level interfaces, mkstemp/mkdtemp, are available for this use case. The mktemp(1) utility is a perfect candidate to fill this gap. Its interface is fairly simple and mostly consistent across various implementations, however not without some differences. I evaluated GNU, LSB, NetBSD, FreeBSD, OpenBSD, Illumos, Solaris, sbase, toybox, busybox implementations and here is what I found: - FreeBSD, NetBSD accept multiple templates. Others do not. - FreeBSD does not specify -p option. Others do. - LSB does not specify -d and -p options. Others do. - FreeBSD, NetBSD accept parameter for -t option. Others do not. - FreeBSD, NetBSD use -t option to specify prefix. Others use it to explicitly tell mktemp to create temporary file in temporary directory rather than in current directory. - All have different default value for template. - All have different requirements regarding how many Xs template should contain, but it seems they all accept six Xs. - sbase, Illumos, Solaris override -p parameter with TMPDIR value if it is set. Others do not. - GNU overrides -p parameter with TMPDIR value or /tmp if parameter is empty string. Others do not. - OpenBSD, Illumos, Solaris(not sure), toybox do not allow '/' in template if -p option is passed. Others do. Given that, I think mktemp interface is not completely lost and below is my attempt to make it portable. |
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| Desired Action |
Standardize mktemp utility. Here is the most minimal and portable example: NAME mktemp - create temporary unique file or directory SYNOPSIS mktemp [-dqu] [-p directory] [template] DESCRIPTION mktemp creates a temporary file based on a template as if by calling mkstemp(3). If no template is specified, an implementation-defined value shall be used instead. If template does not contain exactly six Xs at the end, the behavior is unspecified. If template does not contain '/', the file shall be created in the current directory. Otherwise, the file shall be created by its path. The filename of created temporary file shall be written to the standard output. OPTIONS -d Create directory instead of file as if by calling mkdtemp(3). -p directory Change directory where temporary file will be created. With this option, it is unspecified what happens if template contains '/'. If TMPDIR is set, it is unspecified whether its value take precedence over passed parameter or vice versa. If passed parameter is empty string, the behavior is unspecified. -q Fail silently if an error occurs. -u Operate in unsafe mode. A unique name is generated, but the temporary file shall be unlinked before mktemp exits. Use of this option is not encouraged. SEE ALSO mkdtemp(3), mkstemp(3) |
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Notes |
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(0006038) steffen (reporter) 2022-11-08 23:30 |
While i accept it as natural as it is so widely used, please note that POSIX says for pathchk(1): The pathchk utility was new for the ISO POSIX-2: 1993 standard. It, along with the set −C(noclobber) option added to the shell, replaces the mktemp, validfnam, and create utilities that appeared in early proposals. So what you do is if ( set -C ) >/dev/null 2>&1; then set +C else # For heaven's sake auto-redirect on SunOS/Solaris if [ -f /usr/xpg4/bin/sh ] && [ -x /usr/xpg4/bin/sh ]; then exec /usr/xpg4/bin/sh "${0}" "${@}" else synopsis 1 'sh(1)ell without "set -C" (for safe temporary file creation)' fi fi and then old_umask=`umask` umask 077 i=1 while :; do tmpfile="${tmpdir}/MYNAME-${i}.tmp" ( set -C : > "${tmpfile}" ) >/dev/null 2>&1 && break i=`expr ${i} + 1` if [ ${i} -gt ${max} ]; then echo >&2 'Cannot create a temporary file within '"${tmpdir}" exit ${EX_TEMPFAIL} fi done trap "exit ${EX_TEMPFAIL}" HUP INT QUIT PIPE TERM trap "trap \"\" HUP INT QUIT PIPE TERM EXIT; rm -f ${tmpfile}" EXIT umask ${old_umask} ..after finding a tmpdir and doing some other setup. |
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(0006041) illiliti (reporter) 2022-11-09 13:18 |
Yeah, your example should work, but it is not simple. Look at how simple mktemp is: tmpfile=$(mktemp) or directory: tmpdir=$(mktemp -d) mktemp is impossible to misuse unlike shell. Plus it is already more-or-less portable and widespread on all open-source systems. Also unrelated, but it seems that your example does not work with yash when tmpfile is a dangling symlink. Looks like a yash bug. Reported. |
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Issue History |
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| Date Modified | Username | Field | Change |
| 2022-11-08 23:03 | illiliti | New Issue | |
| 2022-11-08 23:03 | illiliti | Name | => Mark Lundblad |
| 2022-11-08 23:03 | illiliti | Section | => Shell and Utilities |
| 2022-11-08 23:03 | illiliti | Page Number | => - |
| 2022-11-08 23:03 | illiliti | Line Number | => - |
| 2022-11-08 23:30 | steffen | Note Added: 0006038 | |
| 2022-11-09 13:18 | illiliti | Note Added: 0006041 | |
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