/usr/bin/blah
$variable is the value from DB.
$variable is less than $threshold
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So you've got embeded newlines in your invocation of the command, and unquoted barewords. What exactly do you want your command to look like when it gets passed to the operating system?

The here document is parsed by the shell, not Perl. It's interesting; I haven't seen this before, and I'm surprised that it works this way. For example, if I put my code from 353223 into /tmp/t13 and run strace -e execve -f perl /tmp/t13 I get:

...
[pid  5261] execve("/bin/sh", ["sh", "-c", "/bin/cat << EOF\n24 is the
+ value "...], [/* 37 vars */]) = 0
...
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if($variable < $threshold) {
    my $command = '/usr/bin/blah';
    my $updatestring = << "EOF";
$variable is the value from DB.
$variable is less that $threshold
EOF

    my $UPDATE = `$command $updatestring`;
}
else {
    ...
}
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Does it also fix the error?

I would be intersted in knowing how it's going wrong in the first place... do you have a code example that reproduces the error reliably?

One final thing. In some responses above you suggest you will use system instead. I'm sure you know the difference between using backticks and system, but I thought I should point it out anyway.

system returns $? which you can use to determine success or failure (basically if it's true your command failed). If the command called via system prints to STDOUT then that content will go to the STDOUT of your program. Backticks capture the STDOUT from the command and return that. If you call backticks in a list context each new line of data is returned in each list element. If you call it in scalar context you get a string with embedded newlines.

If you want to give up on backticks but still capture the output of the command then perhaps you might want to use:

open ( COMMAND, " $command $updatestring | ") or die $!;
while(<COMMAND>) {
     ....
}
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I hope this helps

jarich

No, perl should wait for the command to finish before it returns, and even if it didn't should build the entire shell command before executing it. Is this a multithreaded program? Can you give a snippet that actually reproduces the problem? I tried something simple like this:

$threshold=25;

foreach $variable (23..30)
{
  
  if ($variable < $threshold)
  {
    $command = '/bin/cat';
    $UPDATE = `$command << EOF
$variable is the value from DB. 
$variable is less than $threshold
EOF`;
    print "Update: '$UPDATE'\n";
  }
}
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Hi:

Ok, Im beginning to think this might be a problem with the command itself. I just added a print " "; around the $UPDATE section to the EOF piece, and the output looks exactly as it should.

The program should be singlethreaded, although the perl itself was compiled as multithreaded.

BTW, the $command was actually a propriatary sql interface to some strange DB.

BTW, I was looking at the thread of answers behind my question and Davido was refering to a "HERE doc." I've never heard of that before....
-chris

<< introduces a here document. The syntax and name come from the shell; < filename means get the input from a filename, and << means get the input from right here.

You can find more in the perldata(1) manpage, or the manual for your shell.

OTOH, if blah actually wants those strings on the command line you need to make a change:

$UPDATE = `$command << EOF`;
$variable is the value from DB. 
$variable is less that $threshold
EOF
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