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Full Discussion: Efficiently altering and merging files in perl
Top Forums Shell Programming and Scripting Efficiently altering and merging files in perl Post 302905511 by sam05121988 on Thursday 12th of June 2014 03:06:51 AM
Old 06-12-2014
Lightbulb Efficiently altering and merging files in perl
I have two files

Code:
fileA
HEADER LINE A
CommentLine A
Content A
....
....
....
TAILER A

Code:
fileB
HEADER LINE B
CommentLine B
Content B
....
....
....
TAILER B

I want to merge these two files as
Code:
HEADER LINE A
CommentLine A
Content A
....
....
....
Content B
....
....
....
TAILER B

i.e. skip the TAILER line of file A and skip the HEADER and Comment Line of fileB

I am able to do it using the below perl code
Code:
        open ( FA, "$fileA" ) || die("can't open fileA $!");
        open ( FB, "$fileB" ) || die("can't open fileB $!");
        open ( TMP, ">> tmp_file" ) || die("can't open tmp_file $!");

        #reading both files in array
        my @fileA = <FA>;
        my @fileB = <FB>;

        #getting rid of HEADER, Comment line, in fileB
        shift @fileB;
        shift @fileB;

        #getting rid of TAILER in fileA
        pop @fileA;

        my @tmp_file=(@fileA,@fileB);

        foreach ( @tmp_file ){
            print TMP $_;
        }

        close(FA);
        close(FB);
        close(TMP);
        
        rename tmp_file, fileA || die("can't rename tmp_file to fileA);

This code works fine, however I doubt it's efficiency if fileA and fileB are going to be millions of lines (which is the case)
i.e. why read whole file in arrays just to get rid of three lines (will end up using lots of memory)

Can someone suggest a more efficient way of doing this
(answers in perl only)
Last edited by sam05121988; 06-12-2014 at 04:15 AM..
 

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LEARN ABOUT DEBIAN

gri_merge

GRI_MERGE(1)						      General Commands Manual						      GRI_MERGE(1)

NAME

       gri_merge - merge multiple Gri output files into a single PostScript file.

USAGE (style 1):
	      gri_merge [OPTIONS] CxR a.ps b.ps ... > merged_file.ps

       Merges  the  files  onto one page, in 'C' columns and 'R' rows.	The CxR files are given in the order of words on a page.  The page is pre-
       sumed to be 8.5x11in in size, as are all the input files, and the input files are sized to fit, and kept in natural scale.

USAGE (style 2):
	      gri_merge [OPTIONS] xcm ycm enlarge a.ps [b.ps ...] > merged_file.ps

       Where `enlarge' is a scale factor applied after offsetting `xcm' to the right and `ycm' upward.

   EXAMPLE (style 2):
	      The following

       gri_merge 2 12 .5 a.ps 

	      12 12 .5 b.ps 

	      2 2 .5 c.ps 

	      12 2 .5 d.ps > all.ps

       produces 4 panels from gri plots done using margins and sizes as specified in the following lines in a gri commandfile

	      set x margin 2

	      set x size 15

	      set y margin 2

	      set y size 15

       The OPTIONS, available if your 'perl' has 'getopts' library, are:

       -u graylevel -- set graylevel for underlay beneath panels, by default 0.75.

	      Values range from 0 (black) to 1 (white), although a value of precisely 1 means do NOT draw underlay.

       -b graylevel -- Set value for background under individual panels, again 0

	      for black to 1 for white, with 1 meaning no drawing.

       -h     -- Print this help message and quit.

SEE ALSO

       gri(1), gri_unpage(1)

gri_merge							       2009							      GRI_MERGE(1)
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