take decision from output of external command in perl script - perl

Question

I want to take decision based on result of system - external commend's output.
like: In my code I am executing one system command and if that command gives error then I have to do something else something different.
Please help me to achieve this:
This is just algorithm ....... i am not able to get value from result
$result = `dt add $dest_file -c porting`;
if($result = 'error')
{
do something 1
}
else
{
do something 2
}
please suggest me way to retrieve value in $ result
I think in this case I should not use system

Answer 1

We have to know what the dt command is. I'm assuming it's DITrack which behaves in a nice Unixish way which means it returns a non-zero error code when it fails.
When Perl executes a system command, it returns the exit value (sort of...) in $?. If dt is DiTrack, it's a standardly implemented such Unix command, and returns a zero exit code when it works, and returns a non-zero exit code when it doesn't work, you can use the $? to determine if it succeeded or not:
$result = qx(dt add $dest_file -c porting); # qx(...) preferred over back ticks.
if ( $? != 0 ) {
chomp $result;
say qq(Everything is okay! Program returned $result);
}
else {
die qq(Some sort of error has happened);
}
The problem is that $? returns both the exit code, and mode of failure. There's this snippet of code from the system that parses $?:
if ($? == -1) {
print "failed to execute: $!\n";
}
elsif ($? & 127) {
printf "child died with signal %d, %s coredump\n",
($? & 127), ($? & 128) ? 'with' : 'without';
}
else {
printf "child exited with value %d\n", $? >> 8;
}

Answer 2

You might consider using regular expressions:
$result = `dt add $dest_file -c porting`;
if($result =~ /error/)
{
do something 1
}
else
{
do something 2
}
One thing to keep mind is that backticks typically/potentially returns the newline character as well so you need to account for this. Using regex will allow you to get around this quickly.