Assign a variable with 10 character long random string using /dev/random in bash?

Question

Trying to create a 10 character password and assign it to a variable and echo it back to the stdout.

This is the script I've created so far, but it doesn't work. I know there are other ways to do this, but I've never been really good as using the | (pipe) to send information from 1 action to another when it involves more than 1 step.

#!/bin/bash
tmp_pass=0
if [ $tmp_pass=0 ]; then
        tmp_pass=`cat /dev/random`
        tmp_pass=$(head tmp_pass -c 10 | base64)
        echo $tmp_pass
fi

Ideally, what I want is an example like this:

1. Define the variable (eg - tmp_pass)
2. Set variable to 0
3. If variable eq 0 then give it a new assignment
4. Assign the variable the result of this:
   1. Generate random string
   2. Grab the first 20 bytes of the random string
   3. Encode it as base64
   4. Cut it to the first 10 characters of the base64

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Note: This was not shown in my original script up above, but it did see it once using echo filename(1:10) or something like that to limit it to echo the first 10 characters of line 1.

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I understand this could be done on 1 single line, but am unsure of how to write it out, any examples would be most appreciated.

Answer 1

The problem here is that you're trying to read an input stream with cat /dev/random, which by itself will never terminate (same thing as trying to do cat /dev/stdin for example). You can fix it by doing something like

#!/bin/bash
tmp_pass=0
if [ $tmp_pass = 0 ]; then
        tmp_pass=`head -c 10 /dev/random | base64`
        echo "${tmp_pass:0:10}" #cut to 10 characters after base64 conversion
fi

Answer 2

Add whatever special characters you would like to have in the password and stay away from /dev/random, it will run out of data and look like it is hanging.

tr -dc 'a-zA-Z0-9' < /dev/urandom | head -c10