04-24-2014
Some additional explanation might be helpful. The awk program is going to process the first file all the way through and then it will process the second file. NR is the total number of records seen so far. FNR is the total number of record seen from the current input file. If FNR == NR we are reading the first file. During the sceond file NR will be larger than FNR.
Look at FNR==NR {f1[$0];next}. While we are reading the first file the code in the braces will be run. f1[$0]; cause an array element to pop into existence. And the next just says we are done with the current record. So during the processing of the first file we are simply building up an array with one element for each unique input line.
During the processing of the second file, we skip the above code and proceed to the second snippet of code: !($1 in f1). This just asks if $1 can be be found in the array. Actually the explanation point flip the questions so it really asks if the record cannot be found in the array. But here we have nothing in braces to tell us what to do. So we do the default action which is to print the current record.
$0 is the whole input record. $1 is the the first field. So we compare the whole input record of the first file to first field of the second file.
Last edited by Scrutinizer; 04-24-2014 at 03:53 PM..
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LEARN ABOUT REDHAT
pdl::char
Char(3) User Contributed Perl Documentation Char(3)
NAME
PDL::Char -- PDL subclass which allows reading and writing of fixed-length character strings as byte PDLs
SYNOPSIS
use PDL;
use PDL::Char;
my $pchar = PDL::Char->new( [['abc', 'def', 'ghi'],['jkl', 'mno', 'pqr']] );
$pchar->setstr(1,0,'foo');
print $pchar; # 'string' bound to "", perl stringify function
# Prints:
# [
# ['abc' 'foo' 'ghi']
# ['jkl' 'mno' 'pqr']
# ]
print $pchar->atstr(2,0);
# Prints:
# ghi
DESCRIPTION
This subclass of PDL allows one to manipulate PDLs of 'byte' type as if they were made of fixed length strings, not just numbers.
This type of behavior is useful when you want to work with charactar grids. The indexing is done on a string level and not a character
level for the 'setstr' and 'atstr' commands.
This module is in particular useful for writing NetCDF files that include character data using the PDL::NetCDF module.
FUNCTIONS
new
Function to create a byte PDL from a string, list of strings, list of list of strings, etc.
# create a new PDL::Char from a perl array of strings
$strpdl = PDL::Char->new( ['abc', 'def', 'ghij'] );
# Convert a PDL of type 'byte' to a PDL::Char
$strpdl1 = PDL::Char->new (sequence (byte, 4, 5)+99);
$pdlchar3d = PDL::Char->new([['abc','def','ghi'],['jkl', 'mno', 'pqr']]);
string
Function to print a character PDL (created by 'char') in a pretty format.
$char = PDL::Char->new( [['abc', 'def', 'ghi'], ['jkl', 'mno', 'pqr']] );
print $char; # 'string' bound to "", perl stringify function
# Prints:
# [
# ['abc' 'def' 'ghi']
# ['jkl' 'mno' 'pqr']
# ]
# 'string' is overloaded to the "" operator, so:
# print $char;
# should have the same effect.
setstr
Function to set one string value in a character PDL. The input position is the position of the string, not a character in the string. The
first dimension is assumed to be the length of the string.
The input string will be null-padded if the string is shorter than the first dimension of the PDL. It will be truncated if it is longer.
$char = PDL::Char->new( [['abc', 'def', 'ghi'], ['jkl', 'mno', 'pqr']] );
$char->setstr(0,1, 'foobar');
print $char; # 'string' bound to "", perl stringify function
# Prints:
# [
# ['abc' 'def' 'ghi']
# ['foo' 'mno' 'pqr']
# ]
$char->setstr(2,1, 'f');
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# [
# ['abc' 'def' 'ghi']
# ['foo' 'mno' 'f'] -> note that this 'f' is stored "f "
# ]
atstr
Function to fetch one string value from a PDL::Char type PDL, given a position within the PDL. The input position of the string, not a
character in the string. The length of the input string is the implied first dimension.
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perl v5.8.0 2001-05-27 Char(3)