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Full Discussion: How to randomly select lines from a text file
Top Forums UNIX for Dummies Questions & Answers How to randomly select lines from a text file Post 302720231 by gary_w on Tuesday 23rd of October 2012 04:05:11 PM
Old 10-23-2012
For the fun of it here's another way that does not use awk although the awk version will be more efficient. This has the overhead of creating the pipeline repeatedly which should be avoided for good practice. Also I believe the ksh RANDOM built-in has a limit of 32767 that must be considered if the file is large.
Code:
$ cat x
##
## x nbr_of_lines_wanted  filename
##
#!/bin/ksh

iterations=$1
file="$2"

((lines_avail=$(wc -l < "$file")+1))

while (( $iterations > 0 )); do
  head -$((${RANDOM} % $lines_avail)) "$file" | tail -1
  (( iterations=$iterations - 1 ))
done

exit 0

This is actually a good example of how a seemingly simple solution for a small file can end up burning you on performance and system limitations should you need to run it on a much larger file
or a system that may see increased load in the future.
Typically when you see a long command line or pipeline like this being done a large number of times (especially a user-enterable number of times) it should
be a red flag warning that there will most likely be a more efficient way of structuring the program.
Last edited by gary_w; 10-23-2012 at 05:11 PM..
This User Gave Thanks to gary_w For This Post:
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LEARN ABOUT HPUX

fmt

fmt(1)							      General Commands Manual							    fmt(1)

NAME

       fmt - format text

SYNOPSIS

       width] [file...]

DESCRIPTION

       The  command is a simple text formatter that fills and joins lines to produce output lines of (up to) the number of characters specified in
       the width option.  The default width is 72.  concatenates the arguments.  If none are given, formats text from the standard input.

       Blank lines are preserved in the output, as is the spacing between words.  does not fill lines beginning with a	period	for  compatibility
       with Nor does it fill lines starting with

       Indentation is preserved in the output and input lines with differing indentation are not joined (unless is used).

       can also be used as an in-line text filter for the command:

       reformats the text between the cursor location and the end of the paragraph.

   Options
       recognizes the following options:

	      Crown margin mode.
		    Preserve the indentation of the first two lines within a paragraph and align the left margin of each subsequent line with that
		    of the second line.  This is useful for tagged paragraphs.

	      Split lines only.
		    Do not join short lines to form longer ones.  This prevents sample lines of code, and other such "formatted" text, from  being
		    unduly combined.

	      Fill output lines to up to
		    width columns.

WARNINGS

       The width option is acceptable for BSD compatibility, but it may go away in future releases.

SEE ALSO

       nroff(1), vi(1).

																	    fmt(1)
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