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Full Discussion: How to read and write a random row from a file?
Top Forums UNIX for Dummies Questions & Answers How to read and write a random row from a file? Post 302194392 by Smiling Dragon on Monday 12th of May 2008 09:18:24 PM
Old 05-12-2008
If you need it to be truly random, you'll need a suitable random number generator.

Once you have 100 random (or predefined if that's all you need) numbers, normalise them against the number of lines in your file (I'd suggest you select 100 numbers between 0 and 1, then multiply that by the lines in the file). That will give you a list of 100 lines numbers.
Code:
#!/bin/sh
# make LINES contain a space seperated list of your line numbers
INPUT="abc.txt"
OUTPUT="test.txt"
rm -f $OUTPUT
for line in $LINES
do
  head -$line $INPUT | tail -1 >> $OUTPUT
done

It's clumsy and won't be very quick (especially for lines further into the file) but it'll do the job.

A better solution would be to seek into the file the correct distance and just dd out the required data.
 

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LEARN ABOUT CENTOS

zlarnv

zlarnv.f(3)							      LAPACK							       zlarnv.f(3)

NAME

       zlarnv.f -

SYNOPSIS

   Functions/Subroutines
       subroutine zlarnv (IDIST, ISEED, N, X)
	   ZLARNV returns a vector of random numbers from a uniform or normal distribution.

Function/Subroutine Documentation
   subroutine zlarnv (integerIDIST, integer, dimension( 4 )ISEED, integerN, complex*16, dimension( * )X)
       ZLARNV returns a vector of random numbers from a uniform or normal distribution.

       Purpose:

	    ZLARNV returns a vector of n random complex numbers from a uniform or
	    normal distribution.

       Parameters:
	   IDIST

		     IDIST is INTEGER
		     Specifies the distribution of the random numbers:
		     = 1:  real and imaginary parts each uniform (0,1)
		     = 2:  real and imaginary parts each uniform (-1,1)
		     = 3:  real and imaginary parts each normal (0,1)
		     = 4:  uniformly distributed on the disc abs(z) < 1
		     = 5:  uniformly distributed on the circle abs(z) = 1

	   ISEED

		     ISEED is INTEGER array, dimension (4)
		     On entry, the seed of the random number generator; the array
		     elements must be between 0 and 4095, and ISEED(4) must be
		     odd.
		     On exit, the seed is updated.

	   N

		     N is INTEGER
		     The number of random numbers to be generated.

	   X

		     X is COMPLEX*16 array, dimension (N)
		     The generated random numbers.

       Author:
	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

       Date:
	   September 2012

       Further Details:

	     This routine calls the auxiliary routine DLARUV to generate random
	     real numbers from a uniform (0,1) distribution, in batches of up to
	     128 using vectorisable code. The Box-Muller method is used to
	     transform numbers from a uniform to a normal distribution.

       Definition at line 100 of file zlarnv.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2							  Tue Sep 25 2012						       zlarnv.f(3)
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