[SOLVED] Any rand() / srand() examples?

andrew.comly · 04-29-2016, 09:54 PM

I am learning bash programming language. I would like to better understand the following command in line 6 of Example 9-17 Pseudorandom numbers, using awk (http://www.tldp.org/LDP/abs/html/randomvar.html).

Code:

srand(); print rand()

I try this out in terminal

Code:

$ srand(); print rand()
srand(); print rand()
bash: syntax error near unexpected token `;'
$ srand(5); print rand()
srand(5); print rand()
bash: syntax error near unexpected token `5'
$ srand(); echo $RANDOM
srand(); echo $RANDOM
bash: syntax error near unexpected token `;'

I search (ixquick) the web to only find the following unrelated articles:
http://www.thegeekstuff.com/2010/03/...-in-functions/ (isn't about "srand()", it's about awk)
http://stackoverflow.com/questions/6...g-it-with-unix
https://www.guyrutenberg.com/2007/09/03/seeding-srand/ (C/C++)
https://linuxconfig.org/bash-scripting-tutorial
http://www.delorie.com/gnu/docs/gawk/gawk_134.html (examples don't work)

I looked in the manual pages, rand has no examples, and srand's manual pages have a c programming example. It appears srand is C and not bash programming language.

Do you have to learn awk and gawk before learning some way of using rand() and srand(). Does anyone know how to use this? Any examples? The more simple the example the better.

Michael Uplawski · 04-30-2016, 12:32 AM

[QUOTE=andrew.comly;5538519]I am learning bash programming language. I would like to better understand the following command in line 6 of Example 9-17 Pseudorandom numbers, using awk (http://www.tldp.org/LDP/abs/html/randomvar.html).

Code:

srand(); print rand()

That is not the authentic line from your example code! It should be

Code:

AWKSCRIPT=' { srand(); print rand() } '

and has a different meaning than that of a command to execute on a command-line.

Above, in the introductory comment, it is written

Quote:

# Uses the awk rand() function.

To the variable AWKSCRIPT, is assigned a line of text ' { srand(); print rand() } ' which comprises 2 commands that awk will execute. It does not make sense to have bash execute awk-scripts.

In the previous examples, notably before very first one on the page, the internal Bash function $RANDOM is mentioned. It should now be obvious which command needs awk and which one will run on the bash command-line.

This mystery sorted out, you can lookup both ways to create random numbers in the man-pages.

man awk (then search for rand() )
man bash (then search for RANDOM)

onebuck · 04-30-2016, 09:52 AM

Moved: This thread is more suitable in <Programming> and has been moved accordingly to help your thread/question get the exposure it deserves.