Top Forums Shell Programming and Scripting Don't understand how RS functions in awk Post 302449039 by bartus11 on Saturday 28th of August 2010 03:17:13 AM
Quote:
Originally Posted by joe228
I learn using RS in awk to extract portion of file in this forum which is wonderful solution to the problem. However, I don't understand how exactly it operates.

I don't quite understand the mechanism behind how searching for /DATA2/ can result in extracting the whole section under "DATA2"

sample
=====
DATA1
data11
data12

DATA2
data21
data22

DATA3
data31
data32

$cat sample | awk 'BEGIN {RS=""} /DATA2/'
DATA2
data21
data22

Since RS is set to be empty string, so each line now should be regarded as a field and so I expected printing $1 and $2 would give me the output of DATA1 and data11 but it didn't. Instead, it returned me with what is shown below:

$ cat sample | awk 'BEGIN {RS=""} { print $1 }'
DATA1
DATA2
DATA3
$ cat sample | awk 'BEGIN {RS=""} { print $2 }'
data11
data21
data31

So, can someone explain to me why it behaved this way?? Thanks!
It behaves like that, because setting RS to empty string causes AWK to go into special mode, where it separates records by empty lines, so in your example you end up with three records:
Code:
DATA1        |
data11       |   1st record (NR=1)
data12       |

DATA2        |
data21       |   2nd record (NR=2)
data22       |

DATA3        |
data31       |   3rd record (NR=3)
data32       |

In that mode one more thing is changed. Field separator is now not only space or tab, but also newline. So inside each of those records you end up with three fields:
Code:
DATA1        <=  1st field ($1)
data11       <=  2nd field ($2)   
data12       <=  3rd field ($3)

I hope it cleared things up for you.
 
Test Your Knowledge in Computers #514
Difficulty: Easy
As a general rule, the more a variable is used, the longer the variable name should be.
True or False?

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IGAWK(1)							 Utility Commands							  IGAWK(1)

NAME
igawk - gawk with include files SYNOPSIS
igawk [ all gawk options ] -f program-file [ -- ] file ... igawk [ all gawk options ] [ -- ] program-text file ... DESCRIPTION
Igawk is a simple shell script that adds the ability to have ``include files'' to gawk(1). AWK programs for igawk are the same as for gawk, except that, in addition, you may have lines like @include getopt.awk in your program to include the file getopt.awk from either the current directory or one of the other directories in the search path. OPTIONS
See gawk(1) for a full description of the AWK language and the options that gawk supports. EXAMPLES
cat << EOF > test.awk @include getopt.awk BEGIN { while (getopt(ARGC, ARGV, "am:q") != -1) ... } EOF igawk -f test.awk SEE ALSO
gawk(1) Effective AWK Programming, Edition 1.0, published by the Free Software Foundation, 1995. AUTHOR
Arnold Robbins (arnold@skeeve.com). Free Software Foundation Nov 3 1999 IGAWK(1)

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