in reply to Confusion with finding strings in command output

If there was a success in opening a file, when why would there be any string in error message about not finding a file (unless for perverse reason the command being called lies about the failure)?

You are searching for an exact string not for a partial match in grep.

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Re^2: Confusion with finding strings in command output
by Laurent_R (Canon) on Aug 30, 2014 at 18:55 UTC
    It is a two-step process: first a shell command run under qx to retrieve the output (including STDERR thanks to the shell redirection), and then an analysis of the output.
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[d/l]

      I know that standard error is being redirected. Do look again at OP's code (simplified)... 

      my $SUCCESS = 0;
my %Error   = ( q[No such file or directory] => 1 );

my @out = qx { command here 2>&1 };
my $rc = $?;

if ( $rc == $SUCCESS )
{
  #  As I wrote earlier, if command was sucessful, then why would
  #  there be no-file-found error (under normal conditions)? Else,
  #  exit code cannot be trusted.
  ... = grep { $Error{$_} } @out;
  ...
}
...

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[d/l]
        Hmm, there is a misunderstanding. My point is that we have no idea about what output this line: 
        my @out = qx { command here 2>&1 };

        [download]
        produces, because we don't know what command here is. As an example, if "command here" if a shell find . -name ... -print ... command, it might very well produce successful lines as well as error lines.
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