[SOLVED] Perl coding help!!

ashok.g · 02-04-2010, 08:51 AM

Guys,
Please look at the following input files and the code.
cat temp.txt

Code:

aaaaaaaaaaaaaaaaaaaa1.bbbbbbbbbbbbbbbbbbbb2.cccccccccccccccccccccc
3. ddddddddddddddddddddddddd 4. eeeeeeeeeeeeeeeeeeeeeeee 
5. ffffffffffffff6.ggggggggggggggggggg
.........................

what I want is to insert a newline before every no.This is the tried.

Code:

open TEMP,"temp.txt";
open OUT,">out";
@a=<TEMP>;
foreach(@a)
{
$_=~s/[0-9]/[0-9]\n/;
print OUT $_;
}
close TEMP;

But I am getting the desired output which should be like:

Code:

aaaaaaaaaaaaaaaaaaaa
1.bbbbbbbbbbbbbbbbbbbb
2.cccccccccccccccccccccc
3. ddddddddddddddddddddddddd
4. eeeeeeeeeeeeeeeeeeeeeeee 
5. ffffffffffffff
6.ggggggggggggggggggg

Please assist me.
Thanks in advance.

MTK358 · 02-04-2010, 09:08 AM

Your grammar really doesn't make any sense to me, but to insert a newline before each number use this:

s/([0-9])/\n\1/g;

And feed it the whole file, not the individual chars on at a time!

If you want to handle multi-digit numbers, use this:

s/([0-9]+)/\n\1/g;

ashok.g · 02-04-2010, 11:05 PM

Thank you.It's working.
But, may I know where my code went wrong?
I used

Code:

$_=~s/[0-9]/[0-9]\n/;

$_ which you didn't used takes by default. So, I think there is no mistake here.
=~,used to match and assign at the same time.
s///,used for substitution.
1st [0-9]used to match the digit.
2nd [0-9]used to print a digit. I think the interpreter doesn't know which digit to choose. Is the code wrong went wrong here??
Even though I will not get the output as I were expected, this should print any digit between [0-9] instead of [0-9]. Why this is not happening? Could you please explain me???

Sergei Steshenko · 02-04-2010, 11:10 PM

Quote:

Originally Posted by ashok.g

Thank you.It's working.
But, may I know where my code went wrong?
I used

Code:

$_=~s/[0-9]/[0-9]\n/;

$_ which you didn't used takes by default. So, I think there is no mistake here.
=~,used to match and assign at the same time.
s///,used for substitution.
1st [0-9]used to match the digit.
2nd [0-9]used to print a digit. I think the interpreter doesn't know which digit to choose. Is the code wrong went wrong here??
Even though I will not get the output as I were expected, this should print any digit between [0-9] instead of [0-9]. Why this is not happening? Could you please explain me???

Regarding item in red - you wrongly understand how 's' operator works.

Read

perldoc perlop

- 's' operator is explained there pretty well.

Also, read

perldoc perlretut
perldoc perlre

- both these documents also have explanations on 's' operator.

MTK358 · 02-05-2010, 07:11 AM

Quote:

Originally Posted by ashok.g

2nd [0-9]used to print a digit. I think the interpreter doesn't know which digit to choose. Is the code wrong went wrong here??

Yes. Also, even if it would work, it would put the newline after the digit.

To use the s/// command to replace parts of the original text onto the output, put all the parts you want to retrieve in ()'s. Then use \1, \2 \3, etc. allt the way to \9 to refer to these parenthesized parts.

Example:

$var = 'ab'
$ab =~ s/(a)(b)/\2\1/;

Now $var contains "ba".