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nodger

11-28-2004 08:40 AM

how do i redirect stderr to a file?

This is what I want to do: I have some cgi scripts and I want to debug them by redirecting the standard error to a file.

I know this much: the cgi script is a child process of apache, and each time it runs, apache hands it several enviornment variables (HTTP_HOST, etc), do I have to change the enviornment it runs in or what? Apache can obviously redirect stdout to a socket, so Im sure I can similarly redirect stderr to a file

jlliagre

11-28-2004 09:14 AM

In what language are your scripts written ?

nodger

11-28-2004 09:35 AM

theyre written in c. I know I could just use a errorlog file but some of the libraries Im linking in use stderr so its cleaner in my opinion to just spit everything out to stderr

jlliagre

11-28-2004 10:04 AM

You can add sth like this at the beginning of your code:

Code:

#include <fcntl.h>

#include <stdio.h>

..

  char *logFile="/tmp/mycgi.err";

  int fd;

  if((fd=open(logFile,O_CREAT|O_APPEND|O_WRONLY,0644))!=-1)

  {

    dup2(fd,2);

  }

  else

  {

    perror(logFile);

  }

All stderr output should then go to the logFile.

This is not very robust though if there is a very high load on your cgi (risk of mixed output from concurrent executions).

nodger

11-28-2004 11:08 AM

thanks for that. I guess that dup2 command duplicates the stderr stream and places the result in file

jlliagre

11-28-2004 11:22 AM

The error output stream is in fact redirected, not duplicated, as the previous stderr output is closed during the call.

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