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Could someone help on how to write an bash script to generate a file named inputFile whose content looks like:

0, 334

1, 933

2, 34123

3, 123

These are comma separated values with index and a random number.

-> Running the script without any arguments, should generate the file inputFile with 10 such entries in current directory.

-> You should be able to extend this script to generate any number of entries, for example 100000 entries.

I tried below script but its not as expected, could someone help me to fix this?

RANDOM=$$
num=0

while [[ ${num} -le $1 ]]
do
    echo $num $RANDOM
    (( num = num +1 ))
done
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3
  • If you do really want random numbers just remove the line RANDOM=$$. From man bash: RANDOM: Each time this parameter is referenced, it expands to a random integer between 0 and 32767 Commented Nov 18, 2022 at 5:54
  • 1
    @EdgarMagallon The assignment to RANDOM is outside the loop, so $$ (the shell's pid) is used as the seed of the sequence. At least it varies on each run. Bash Ref Manual does not say how RANDOM is initialised, but I found a post that claimed: gettimeofday (&tv, NULL); sbrand (tv.tv_sec ^ tv.tv_usec ^ getpid ()); Commented Nov 18, 2022 at 10:14
  • @Paul_Pedant oh, that's right! I thought it was setting a new seed every loop but yes, it's outside the loop. And thanks for the last info, that's useful! Commented Nov 18, 2022 at 17:22

1 Answer 1

Reset to default
1

You're not far off.

I'd probably set a variable, say count to the first command line parameter ($1), and then check if it's empty, which case you could set it to 10.

#!/usr/bin/env bash
RANDOM=$$
count="$1"
[[ -z "$count" ]] && count=10

num=0
while [[ ${num} -le ${count} ]]
do
    echo $num, $RANDOM
    (( num = num +1 ))
done > inputFile

Technically that will give you 11 random numbers, not 10, since it starts with 0 and ends with 10, To change that, either start num at 1 (to get 1–10), or use -lt rather then -le (to get 0–9).

Be sure to put a comma in the echo command if you want a comma between the numbers in the output.

You can use any other number than 10 to get more random numbers. bash script.sh 10000.

BTW inputFile is a weird name for an output file.

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