Create a file of a specific size with random printable strings in bash

Question

I want to create a file of a specific size containing only printable strings in bash.

My first thought was to use /dev/urandom:

dd if=/d         


        

Answer 1

You can do it in awk way and customize character set.

This solution is dedicated for Windows bash users - MINGW, because there is no dd, random tools at default MINGW environment.

random_readable.sh Bash script that randomize N characters from defined alphabet:

#!/bin/sh

if [ -z $1 ]; then
    echo "Pass file size as initial parameter"
    exit
fi

SIZE=$1
seed=$( date +%s )

awk -v size="$SIZE" -v seed="$seed" '
# add characters from range (a .. b) to alphabet
function add_range(a,b){
    idx=a;
    while (idx <= b) {
        alphabet[idx] = sprintf("%c",idx)
        idx+=1
    }
}
BEGIN{
    srand(seed);  
    NUM=size;  
    idx=0;  

    # creating alfphabet dictionary
    add_range(32,126)   # all printable
    ## uncomment following lines to random [a-zA-Z0-9]
    # add_range(48,57)    # numbers
    # add_range(65,90)    # LETTERS
    # add_range(97,122)   # letters
    # add_range(33,47)    # operators: !"# .. etc

    # alfphabet to alphanums array
    idx=0
    for (k in alphabet){
        alphanums[idx]=alphabet[k]
        idx+=1
    }
    alphabet_len = idx
    i=0

    # and iterate to random some characters
    idx =0
    while (idx < NUM){                         
        dec =0
        char_idx=int(rand() * alphabet_len)
        char = alphanums[char_idx]
        printf("%s",alphanums[char_idx])
        idx+=1
    }  
}  
' 

Creating file:

random_readable.sh 100 > output.txt