Shell Programming and Scripting

Hi,

I have a sample file, which has a record ..

Code:

</ab><cd>3410</cd>

I need to use a if clause to check ..

Code:

  my $chk=`tail $file | grep "<cd>"| cut -c 1-9`;
   print "\n tag is $chk \n";
   if ( $chk eq "</ab><cd>" )
   { print "\n Needs to be processed \n"}
  else 
   {print "\n No need to process\n"}

Problem is .. when i do $chk eq "</ab><cd>" .. it always prints "No need ..." and if i use $chk == "</ab><cd>" .. it always prints "Needs..."
Can anyone help me with right string comparison.

Thanks

eq is the string equality operator...

tail grabs the last 10 lines by default... You might want tail -1 ... otherwise, you are going to get maybe more than you want.

Otherwise, you might try escaping the forward slash with a backslash as in...

$chk eq "<\/ab><cd>"

Thanks for the reply, quine.
I think when we have it in quotes, it should not matter even if it need backslash ..

My problem is solved, i need to use chomp($chk); .. then it worked fine..

Thanks

If you are searching for a substring/pattern, you can use a regexp:

if ( $chk =~ /<\/ab><cd>/ )

You could also use the index() function. You can look up its usage. If you are checking a string then use "eq".

You should be aware that if your input file has anything in front of the tag set you specified, your program will break. For instance, if the test file's last line contains "Some stuff</ab><cd>3410</cd>" then running the commands you show will set $chk = "Some stuf" and you won't ever know whether the file contained your markers or not!

You could use tail -n 1' to just pick off the final line. Then use regexp to pull out and test the tag of interest from the final line, i.e.:

my $final_line = `tail -n 1 $test_file`;
if ($final_line =~ m#</ab><cd>#) {
print "\n Needs to be processed \n";
}
else {
print "\n No need to process\n"
}

chomp()...

Ah yes, the line still has a newline, so the eq test always fails..

So $final_line =~ m#</ab><cd># using a pattern match makes sense since that would work either way...

Hi,

In perl you can use the "==" and =~ sign for string comparison
and comp used to clear "\n" character at end of the input string

Regards,
Siva Pitchai
Bangalore