P0w3rK!d has asked for the wisdom of the Perl Monks concerning the following question:

I have a program which reads values from a database which are placed into a unique file in /tmp. The file name is echoed from the program when it is created. My perl script is attempting to grab the output from that command by redirecting STDOUT to a file that I can read later ( I need to read the file and process each line for FTP purposes - this code already works). When I execute this portion of code, it never prints out the "foo1". Am I losing STDOUT ..or is the code flaking out on me? 
#!/usr/bin/perl


# just make up a fake file here to create
# and echo the filename of /tmp/foo
$tabfile = "./tabfile";
$logfile = "/tmp/foo";

# send output to file
@args2 = ("$tabfile");
open (STDOUT, ">$logfile") || die "could not open log\n";
unless (system(@args2) == 0) {
       print STDERR "system(@args2) failed: $? $!\n";
       return;
}
close(STDOUT);

print "foo1\n";

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Replies are listed 'Best First'.
Re: Help: STDOUT flaking out?
by busunsl (Vicar) on May 17, 2001 at 17:56 UTC
    STDOUT is a predefined filehandle. When you open a new file with that handle, the old is closed.
    After that you close STDOUT explicitly, so nothing is printed.

    Don't use STDOUT to open a file, use a different name.

[reply]
Re: Help: STDOUT flaking out?
by suaveant (Parson) on May 17, 2001 at 18:01 UTC
    or try this.... 
    #!/usr/bin/perl


  # just make up a fake file here to create
  # and echo the filename of /tmp/foo
  $tabfile = "./tabfile";
  $logfile = "/tmp/foo";

  # send output to file
  @args2 = ("$tabfile");
  {
  local(*STDOUT);
  open (STDOUT, ">$logfile") || die "could not open log\n";
  unless (system(@args2) == 0) {
         print STDERR "system(@args2) failed: $? $!\n";
         return;
  }
  close(STDOUT);
  }
  print "foo1\n";
}

    [download]
    That should temporarily store STDOUT away and when you leave the code block, return its original value... I believe... not tested

    Update you could also use select, open log filehandle OUT say, instead of STDOUT, then do select OUT; all output will go to OUT instead of STDOUT until you do select STDOUT; to put it back...
                    - Ant

[reply]
[d/l]
      This still is not working. The file "tabfile" is a shell script that created the file "FTPData.20010517.111754". I am trying to capture that echoed output and redirect it into a file. Might there be a better way to do this with a pipe or some other mechanism? Please advise :) 
      RESULT:
$ ftp_flow.pl
logfile = /tmp/ftp_flow.111753410117.log
errfile = /tmp/ftp_flow.111753410117.err
FTPData.20010517.111754
$ cat /tmp/ftp_flow.111753410117.log
$

(the file is empty... it should contain 
"FTPData.20010517.111754" as the 1st line)

CODE:
# send output to file
@args2 = ("$tabfile");
local(*LOGFILE);
open (LOGFILE, ">$logfile") || die "could not open log\n";
select(LOGFILE);
unless (system(@args2) == 0) {
        print STDERR "system(@args2) failed: $? $!\n";
        return;
}
close(LOGFILE);

print "foo1\n";
exit (0);

      [download]
[reply]
[d/l]
        you probably really want to just use backticks... 
        # send output to file
###either
  open (LOGFILE, ">$logfile") || die "could not open log\n";
  print LOGFILE `$tabfile`;  
  if($?) {
        print STDERR "$tabfile failed: $?\n";
        return;
  }
  close(LOGFILE);
##or
  `$tabfile > $logfile`;
  if($?) {
        print STDERR "$tabfile failed: $?\n";
        return;
  }
## end or

  print "foo1\n";
  exit (0);

        [download]

                        - Ant
[reply]
[d/l]

        You need to select(STDOUT); after your close(LOGFILE);. Right now, you're still printing to a closed filehandle...

[reply]
[d/l]
[select]
        This works now: Thank you :) 
        # send output to file
@args2 = ("$tabfile");
open (LOGFILE, ">$logfile") || die "could not open log\n";
unless (system(@args2) == 0) {
        print STDERR "system(@args2) failed: $? $!\n";
        return;
}
select(LOGFILE);
close(LOGFILE);

        [download]
[reply]
[d/l]

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