From: Joel âcheskyâ Salomon <JoelCSalomon@Gmail.com>
To: 9fans@cse.psu.edu
Subject: [9fans] non-truncating create
Date: Sun, 8 Oct 2006 23:13:07 -0400 [thread overview]
Message-ID: <f1dec573a0466a32a59881314c144e9f@plan9.jp> (raw)
Still for the Brain-Dead SHell homework assignment...
I’m trying to implement output redirection, > and >>. Truncating
redirect (>) is easy; just use create(2) whether the file exists or
no. The non-truncing option is puzzling me, though. If the file
exists, I need to o = open(oname, OWRITE), then seek(o, 0, 2); if the
file does not exist I need to create it.
How do I check for the existence of a file? I’m thinking about the
following code snippet:
o = open(oname, OWRITE)
rerrstr(errbuf, ERRMAX);
if((strstr(errbuf, "file does not exist") == 0){
complain("cannot open %s: %r", oname);
return;
}else o = create(oname, OWRITE, ~0);
if(o < 0)
...
Is there a cleaner way to accomplish this? Some form of stat(2) that has an explicit “file does not exist” code outside parsing errstr
Of secondary interest: Not that this is production code, but should I
be concerned about race conditions where the file is created by
somebody else between the failed open(2) and the create(2)?
Of tertiary interest: Is there a general use for a library function
complain() that behaves identically to sysfatal(2) except for not
terminating the program?
--Joel
next reply other threads:[~2006-10-09 3:13 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-10-09 3:13 Joel “chesky” Salomon [this message]
2006-10-09 4:00 ` Russ Cox
2006-10-09 6:09 ` Joel “chesky” Salomon
2006-10-09 15:57 ` Russ Cox
2006-10-09 4:01 ` Felipe Bichued
2006-10-09 5:39 ` Joel Salomon
2006-10-09 3:13 Joel “chesky” Salomon
2006-10-09 3:13 Joel “chesky” Salomon
2006-10-09 6:46 Joel “chesky” Salomon
2006-10-09 7:30 ` Steve Simon
2006-10-09 22:38 G. David Butler
2006-10-09 23:36 ` Joel Salomon
2006-10-10 0:03 ` Russ Cox
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=f1dec573a0466a32a59881314c144e9f@plan9.jp \
--to=joelcsalomon@gmail.com \
--cc=9fans@cse.psu.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).