Creating a “Fluff” File Filled with Specified or Random Text

Described below are two different methods for quickly generating a certain size of fluff, or filler, to be inserted into a text file for testing purposes. The first method is to use a single line command which will very quickly fill a file with random text (must have base64 installed). The second method is to use a script that will quickly fill a file with text that the user specifies (there are some limitations).

For the first method, let’s use this scenario: we need to quickly come up with a 2MB file to test a text scanning function within our program and it does not matter what the text is. Running the following command will create this file for us and call it random.txt.

base64 /dev/random | head -c 2000000 > random.txt

For the second method, let’s use this scenario: we need to quickly fill a file with the string “abcdefghijklmnopqrstuvwxyz 123456890n” repeated until the result is 2MB in size in order to test a parsing algorithm in our program. The following script will generate this file for us and call it result.txt. I have tested this script up to 20MB and it took only a few seconds, however, the larger the size, the longer this script will take to run (very inefficient for really large files). At first glance, it seems like a complicated script, but upon second glance you’ll notice that it’s mostly user defined variables and safe guard checks for user input.


# Variables; 2000000 = 2MB
string="abcdefghijklmnopqrstuvwxyz 123456890n"

# File checks so we don't overwrite somebody's important files
if [ -e $tmpfilename ]; then
        echo "File: $tmpfilename exists!"
        echo "This script is going to use this as a temporary file, so either"
        echo "modify the script variable $tmpfilename or remove the file."
        exit 1

if [ -e $filename ]; then
        echo "File: $filename exists!"
        echo "Remove it and restart this script"
        exit 1
        echo -e $string > $filename

# Initialize the variable
size=$(stat -c %s $filename)

# Start the loop, increasing the size of the file 2x until reaching max_size
while [ $size -lt $max_size ]; do
        cat $filename > $tmpfilename
        cat $tmpfilename >> $filename
        size=$(stat -c %s $filename)

# Chop off any excess
head -c $max_size $filename > $tmpfilename
mv $tmpfilename $filename

I believe the first method is fantastic. It creates a file very quickly and it’s easy to understand. I can see room for improvement on the second method. If you have any suggestions, please feel free to share them with me! I would really love to hear it.

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There's 1 Comment So Far

  • Richard Wicks
    June 22nd, 2011 at 7:07 pm

    yes “abcdefghijklmnopqrstuvwxyz 123456890” | head -c 2000000 > result.txt

    does the same thing as your script

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