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Re: Avoiding file-based constraints for tmp files (ws Re: [minor] umask
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From: |
Greg Wooledge |
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Subject: |
Re: Avoiding file-based constraints for tmp files (ws Re: [minor] umask 400 causes here-{doc,string} failure) |
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Date: |
Thu, 15 Mar 2018 08:37:39 -0400 |
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User-agent: |
NeoMutt/20170113 (1.7.2) |
On Wed, Mar 14, 2018 at 06:45:15PM -0700, L A Walsh wrote:
> Is relying on HERE-doc implementation something that is portable? Is it
> required by POSIX? Still a few things to remember...
POSIX says "no":
It is unspecified whether the file descriptor is opened as a regular
file, a special file, or a pipe. Portable applications cannot rely on
the file descriptor being seekable (see XSH lseek).
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_07_04
That said, I think a lot of scripts *do* bend this rule and rely on
the here-document creating a seekable temp file, because this has been
the common practice across many different shells for a long time.