Programming Forums > Script Programming > Perl

centurion555 · Nov 13th, 2008, 5:10 PM

Hi every one,
I am trying to write a sed/awk command to select every third line from a text file. I have text files with 1200 lines and I need to cut every third line starting from 1 line (no header or footer in the file.)
Thanks in advance
centurion

centurion555 · Nov 16th, 2008, 9:40 AM

Hi every one,
I am trying to write a perl command to select every third line from a text file. I have text files with 1200 lines and I need to cut every third line starting from 1st line (no header or footer in the file.)
Thanks in advance
centurion

Freaky Chris · Nov 16th, 2008, 9:50 AM

Quote:

Originally Posted by centurion555

Hi every one,
I am trying to write a perl command to select every third line from a text file. I have text files with 1200 lines and I need to cut every third line starting from 1st line (no header or footer in the file.)
Thanks in advance
centurion

read it line by line, and count three before you actually do anything with the lines

Chris

centurion555 · Nov 18th, 2008, 5:48 PM

Hi Chris,
Thanks for your reply. I am new to perl. I don't understand what this

,[->+>+<<]>>[-<<+>>]>++++++++[-<++++++++>]<+[-<->]>+<<[[-]+++++++++++++++.[-]>]>>[+++++++++.[-]],

means and how to use this in perl script. I have perl installed but i never saw a syntax like this.
Centurion

lectricpharaoh · Nov 18th, 2008, 7:11 PM

Quote:

Originally Posted by centurion555

I am new to perl. I don't understand what this

,[->+>+<<]>>[-<<+>>]>++++++++[-<++++++++>]<+[-<->]>+<<[[-]+++++++++++++++.[-]>]>>[+++++++++.[-]],

means and how to use this in perl script. I have perl installed but i never saw a syntax like this.

That is not Perl; it's a program in the brainfuck language (a language designed to be confusing, hence the name). It's also a sig, and not part of the message text itself, thus not part of his reply to you.

To expand on his initial post, you need to read the file line by line, and discard every line that's not a multiple of three. Generally, the way you do this is by writing the lines you want to keep to a new file, so that when you're done, it will contain every third line of the first file.

I've never used Perl, but here is pseudocode that you should be able to adapt into Perl:

pseudocode Syntax (Toggle Plain Text)

inFile = open("SourceFile")
outfile = open("DestinationFile")
linecount = 0
while(inFile.containsMoreLines())
{
  increment lineCount
  textLine = inFile.readLine()
  if((lineCount mod 3) equals 0)
    outFile.writeLine(textLine)
}
inFile.close()
outFile.close()

Chetanji · Nov 21st, 2008, 10:34 AM

Are you using dos or linux?

Is it possible that the third line is a duplicate of another line?

This fact would make it easy to remove the duplicate and only print out the unique lines.
Chetanji

Chetanji · Nov 22nd, 2008, 4:39 AM

Quote:

Originally Posted by centurion555

Hi every one,
I have text files with 1200 lines and I need to cut every third line starting from 1st line (no header or footer in the file.)centurion

If this third line is a duplicate of another line, ALWAYS.
Then you can use the a Awk program that mimicks the Unix sort command
"sort -u -k1,1".
Please give a little more information of what you are trying to achieve and what you data is.

Thanks,
Chetanji

centurion555 · Nov 29th, 2008, 4:10 PM

Hello Chetanji,
I am using linux. All lines in the file are unique. No duplicate lines.
Centurion

Quote:

Originally Posted by Chetanji

Are you using dos or linux?

Is it possible that the third line is a duplicate of another line?

This fact would make it easy to remove the duplicate and only print out the unique lines.
Chetanji

Chetanji · Dec 1st, 2008, 7:32 AM

Linux makes it easier.

please give 9 line sample of your text.

Chetanji

Infinite Recursion · Dec 1st, 2008, 8:03 AM

No example of data needed.

awk 'NR%3==0' FILENAME

where FILENAME is the name of your data file. You can replace 3 with N and get the Nth line as well.

Nov 13th, 2008, 5:10 PM	#1
centurion555 Newbie Join Date: Nov 2008 Posts: 9 Rep Power: 0	Selecting every third line Hi every one, I am trying to write a sed/awk command to select every third line from a text file. I have text files with 1200 lines and I need to cut every third line starting from 1 line (no header or footer in the file.) Thanks in advance centurion

Nov 16th, 2008, 9:40 AM	#2
centurion555 Newbie Join Date: Nov 2008 Posts: 9 Rep Power: 0	Cutting every third line Hi every one, I am trying to write a perl command to select every third line from a text file. I have text files with 1200 lines and I need to cut every third line starting from 1st line (no header or footer in the file.) Thanks in advance centurion

Nov 18th, 2008, 5:48 PM	#4
centurion555 Newbie Join Date: Nov 2008 Posts: 9 Rep Power: 0	Re: Cutting every third line Hi Chris, Thanks for your reply. I am new to perl. I don't understand what this ,[->+>+<<]>>[-<<+>>]>++++++++[-<++++++++>]<+[-<->]>+<<[[-]+++++++++++++++.[-]>]>>[+++++++++.[-]], means and how to use this in perl script. I have perl installed but i never saw a syntax like this. Centurion

Nov 21st, 2008, 10:34 AM	#6
Chetanji programmer Join Date: Nov 2008 Location: In the present moment Posts: 19 Rep Power: 0	Re: Selecting every third line Are you using dos or linux? Is it possible that the third line is a duplicate of another line? This fact would make it easy to remove the duplicate and only print out the unique lines. Chetanji

Dec 1st, 2008, 7:32 AM	#9
Chetanji programmer Join Date: Nov 2008 Location: In the present moment Posts: 19 Rep Power: 0	Re: Selecting every third line Linux makes it easier. please give 9 line sample of your text. Chetanji

Dec 1st, 2008, 8:03 AM	#10
Infinite Recursion Programming Guru Join Date: Jul 2004 Location: United States Posts: 3,484 Rep Power: 10	Re: Selecting every third line No example of data needed. awk 'NR%3==0' FILENAME where FILENAME is the name of your data file. You can replace 3 with N and get the Nth line as well. __________________ http://jasonpowers.net "There are a thousand hacking at the branches of evil to one who is striking at the root."

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Programming Forums > Script Programming > Perl

Selecting every third line