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open stdin a second time

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  open stdin a second time FBert <anon@devnull.invalid> - 2011-11-11 20:11 +0000
    Re: open stdin a second time James Kuyper <jameskuyper@verizon.net> - 2011-11-11 15:31 -0500
    Re: open stdin a second time Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-11 20:12 -0500

#13117 — open stdin a second time

Hi,

I´m opening stdin to get a file and pass it through a pipe.

razor=popen("/var/qmail/bin/razor-check -home=/var/qmail/razor",
"w");
while((ret=fread(linha,1,sizeof(linha),stdin))>0)
{fwrite(linha,1,sizeof(linha),razor);}
pclose(razor);

After that, if razor returns me an error I want to send an email with
the original message attached...but how can I re-read stdin to do
that.

I do not want to save the message to a temp file or save it to memory
for i/o questions. Is there a way to re-read stdin ? 

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#13119

On 11/11/2011 03:11 PM, FBert wrote:
> Hi,
> 
> I´m opening stdin to get a file and pass it through a pipe.
> 
> razor=popen("/var/qmail/bin/razor-check -home=/var/qmail/razor",
> "w");
> while((ret=fread(linha,1,sizeof(linha),stdin))>0)
> {fwrite(linha,1,sizeof(linha),razor);}
> pclose(razor);
> 
> After that, if razor returns me an error I want to send an email with
> the original message attached...but how can I re-read stdin to do
> that.
> 
> I do not want to save the message to a temp file or save it to memory
> for i/o questions. Is there a way to re-read stdin ? 

That depends upon what kind stream stdin is. The message has to be
stored somewhere if you're to retrieve it. If stdin is a terminal, for
instance, if you don't save the message yourself, then it isn't saved
anywhere, and you're out of luck.

On the other hand, if stdin is a file, the information is saved - in
that file. You can use rewind() to go back to the beginning of the file,
or either fseek() or fsetpos() to go back to specific saved positions in
the file.

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#13157

On 11/11/2011 3:11 PM, FBert wrote:
> Hi,
>
> I´m opening stdin to get a file and pass it through a pipe.
>
> razor=popen("/var/qmail/bin/razor-check -home=/var/qmail/razor",
> "w");
> while((ret=fread(linha,1,sizeof(linha),stdin))>0)
> {fwrite(linha,1,sizeof(linha),razor);}
> pclose(razor);
>[...]

     See James Kuyper's response.  In addition, note that the third
argument to fwrite() should almost certainly be `ret', because there's
an excellent chance that the tail end of `linha' will be whatever was
left over from the next-to-last input line.  (For extra credit, examine
the value returned by fwrite() to see whether it actually worked.)

-- 
Eric Sosman
esosman@ieee-dot-org.invalid

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