Solved

0 vs '': detecting

Posted on 2003-11-17
3
212 Views
Last Modified: 2010-03-04
Have a program where I output a tab separated file into simple flat XML:

while (<STDIN>) {
  chomp;
  $line = $_;
  @Elems = split(/\t/, $line);

  print "<entry name=\"", $Elems[0], "\" id=\"", $Elems[1], "\"";
  if ($Elems[2] != '') {
      print " default=\"", $Elems[2], "\""
  }
  print "/>\n";

My problem is the line   if ($Elems[2] != '') {
Sometimes the default is 0 and when this is so the the next line is not executed (the same as if there was no value at all).

For example on the following sample:
abc      12
def      13      0
ghi      14      1
fjk      15      

the output is:
<entry name="abc" id="12"/>              
<entry name="def" id="13"/>              
<entry name="ghi" id="14" default="1"/>
<entry name="fjk" id="15"/>

How do I get around this?
0
Comment
Question by:davelane
3 Comments
 
LVL 3

Accepted Solution

by:
BioI earned 65 total points
ID: 9764914
I think the problem is that you use != for a numeric value.
When you change "!=" into "ne", I think it will work.
When you use in the beginning of your script the addition of "-w" in the first line:
#!/usr/bin/per -w
you should have got an error message like:
Argument "" isn't numeric in numeric ne (!=) at ./yourscript.pl line xx.


while (<STDIN>) {
  chomp;
  $line = $_;
  @Elems = split(/\t/, $line);

  print "<entry name=\"", $Elems[0], "\" id=\"", $Elems[1], "\"";
  if ($Elems[2] ne '') {
     print " default=\"", $Elems[2], "\""
  }
  print "/>\n";
0
 
LVL 20

Assisted Solution

by:jmcg
jmcg earned 60 total points
ID: 9764990
I thought this was answered in the Perl FAQ, but I didn't find it in the place where I thought it should be.

Perl has both numeric comparison operators and string comparison operators. You were using a numeric comparison.


if ($Elems[2] != '') { # numeric comparison


And the empty string evaluates numerically to 0 (as do all other strings that do not look sufficiently like numbers). What you may have wanted to do was use a string comparison:


if ($Elems[2] ne '') { # string comparison


Let me just add one more complication. Variables in perl can also have a "value" called 'undef', or undefined. You can't use comparison operators to detect it, it has a special predicate function 'defined'. When used in comparisons, it acts the same as an empty string.

0
 

Author Comment

by:davelane
ID: 9765135
Thanks guys for the speedy replies. Did the trick. :)
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

I have been pestered over the years to produce and distribute regular data extracts, and often the request have explicitly requested the data be emailed as an Excel attachement; specifically Excel, as it appears: CSV files confuse (no Red or Green h…
There are many situations when we need to display the data in sorted order. For example: Student details by name or by rank or by total marks etc. If you are working on data driven based projects then you will use sorting techniques very frequently.…
Explain concepts important to validation of email addresses with regular expressions. Applies to most languages/tools that uses regular expressions. Consider email address RFCs: Look at HTML5 form input element (with type=email) regex pattern: T…
This Micro Tutorial hows how you can integrate  Mac OSX to a Windows Active Directory Domain. Apple has made it easy to allow users to bind their macs to a windows domain with relative ease. The following video show how to bind OSX Mavericks to …

910 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

25 Experts available now in Live!

Get 1:1 Help Now