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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 PHP

rename

RENAME(3)								 1								 RENAME(3)

rename - Renames a file or directory

SYNOPSIS

       bool rename (string  $oldname, string  $newname, [resource  $context])

DESCRIPTION

	Attempts to rename $oldname to $newname, moving it between directories if necessary. If $newname exists, it will be overwritten.

PARAMETERS

	      o $oldname
		-

	      Note

		      The old name. The wrapper used in $oldname must match the wrapper used in $newname.

	      o $newname
		- The new name.

	      o $context
		-

	      Note

		     Context support was added with PHP 5.0.0. For a description of contexts, refer to "Streams".

RETURN VALUES

	Returns TRUE on success or FALSE on failure.

CHANGELOG

       +--------+---------------------------------------------------+
       |Version |						    |
       |	|						    |
       |	|		     Description		    |
       |	|						    |
       +--------+---------------------------------------------------+
       | 5.3.1	|						    |
       |	|						    |
       |	| rename(3)  can  now rename files across drives in |
       |	| Windows.					    |
       |	|						    |
       | 5.0.0	|						    |
       |	|						    |
       |	| rename(3) can now also  be  used  with  some	URL |
       |	| wrappers. Refer to "Supported Protocols and Wrap- |
       |	| pers" for a listing  of  which  wrappers  support |
       |	| rename(3).					    |
       |	|						    |
       | 4.3.3	|						    |
       |	|						    |
       |	| rename(3)  may now be able to rename files across |
       |	| partitions on *nix based  systems,  provided	the |
       |	| appropriate permissions are held. Warnings may be |
       |	| generated if the destination	filesystem  doesn't |
       |	| permit chown() or chmod() system calls to be made |
       |	| on files  --	for  example,  if  the	destination |
       |	| filesystem is a FAT filesystem.		    |
       |	|						    |
       +--------+---------------------------------------------------+
EXAMPLES

       Example #1

	      Example with rename(3)

	      <?php
	      rename("/tmp/tmp_file.txt", "/home/user/login/docs/my_file.txt");
	      ?>

SEE ALSO

       copy(3), unlink(3), move_uploaded_file(3).

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