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How to compare data from 2 zip files and capture the new records from file2 to a new file

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Top Forums Shell Programming and Scripting How to compare data from 2 zip files and capture the new records from file2 to a new file
# 8  
Old 12-05-2011
Quote:
Originally Posted by Corona688
Those should be .gz or .z, not .zip.
Code:
$ man zcat
 
GZIP(1)                                                                GZIP(1)
 
 
 
NAME
       gzip, gunzip, zcat - compress or expand files
 
SYNOPSIS
       gzip [ -acdfhlLnNrtvV19 ] [-S suffix] [ name ...  ]
       gunzip [ -acfhlLnNrtvV ] [-S suffix] [ name ...  ]
       zcat [ -fhLV ] [ name ...  ]
 
DESCRIPTION
       Gzip  reduces  the  size  of  the  named  files using Lempel-Ziv coding
       (LZ77).  Whenever possible, each file  is  replaced  by  one  with  the
       extension .gz, while keeping the same ownership modes, access and modi-
       fication times.  (The default extension is -gz for VMS,  z  for  MSDOS,
       OS/2  FAT, Windows NT FAT and Atari.)

Actual zip is difficult to use in a pipe chain.

Knowing what you have, I'd do this:

Code:
mkfifo data1 data2
zcat < a.gz > data1 &
zcat < b.gz > data2 &
 
awk 'BEGIN { while(getline <"data1") L[$0]=1 }; !L[$0]' data2
 
wait
rm -f data1 data2

---------- Post updated at 03:17 PM ---------- Previous update was at 03:13 PM ----------

A simplified version:

Code:
mkfifo data1
zcat < a.zip > data1 &
zcat < b.zip | awk 'BEGIN { while(getline <"data1") L[$0]=1 }; !L[$0]'
wait
rm data1

Thanks !! This code is working as expected. I tried with less than a million records in each file and it gave me the output in less than a minute. But when i tried with 27 million records in each file, it is still executing from an hour. Will this consume lot of disk space ? Is there a way to get the output faster ?
# 9  
Old 12-05-2011
Quote:
Originally Posted by koneru
But when i tried with 27 million records in each file, it is still executing from an hour. Will this consume lot of disk space ? Is there a way to get the output faster ?
It has to hold the complete, uncompressed contents of "a" in memory to tell if any lines from "b" exist in it. How else would it know, when it can't make any assumptions like ordering? This doesn't take disk space but takes as much memory as it needs to hold "a" uncompressed.

That can't be simplified or sped up without sorting the input files first -- which takes time itself, and would alter the order of output.
Last edited by Corona688; 12-05-2011 at 02:57 PM..
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