Generating Predictable Random Strings in Linux

2 February 2026 • linux

Often, you will want to generate random strings for identifiers, passwords or other use cases.

The advice I often see is to use openssl rand -base64 32. This method does work, but comes with some disadvantages:

• Base64 encoding can leave you with /, = and + characters, which are usually undesirable
• Specifying a number of bytes can make it bit tricky to get the string length you want

My preferred method (which I keep forgetting so I’m writing it down…) is to use:

$ tr -dc 'A-Za-z0-9' </dev/urandom | head -c 12
t3TpDEwZjkZr

This gives you a predictable length output, and you know exactly what characters will be included. If you want to include other characters, just add them to the tr command:

$ tr -dc 'A-Za-z0-9_\-!' </dev/urandom | head -c 12
!sn_CfP-LgI6

(Note the \ for the - character!)