How to create a random string of random length

Question

I'm looking for a way to create a string of random letters and random length. So whenever the command is used I get different strings.

\documentclass[11pt]{article}
\newcommand{\randomstring}{...}

\begin{document}
\randomstring
\randomstring

\end{document}

The out put could be

xkakhiw

or

khaggfpze

I think you got the idea. Could someone give me a hint, where to start?

Answer 1

Using Manuel's idea:

\documentclass{article}
\ExplSyntaxOn
\NewExpandableDocumentCommand{\randomstring}{}
 {
  \randomstring_make:
 }
\NewDocumentCommand{\defrandomstring}{sm}
 {
  \IfBooleanTF{#1}{\cs_set:Npe}{\cs_new:Npe} #2 { \randomstring_make: }
 }
\NewDocumentCommand{\setrandomstringlength}{m}
 {
  \int_set:Nn \l_randomstring_length_int { #1 }
 }
\int_new:N \l_randomstring_length_int
\cs_new:Nn \randomstring_make:
 {
  \prg_replicate:nn { \int_rand:n { \l_randomstring_length_int } }
   {
    \int_to_alph:n { \int_rand:n { 26 } }
   }
 }
\ExplSyntaxOff
\setrandomstringlength{26}
\begin{document}
\randomstring
\randomstring
\randomstring
\defrandomstring{\foo}
\texttt{\meaning\foo}
\setrandomstringlength{4}
\randomstring
\randomstring
\defrandomstring*{\foo}
\texttt{\meaning\foo}
\end{document}

With \setrandomstringlenght we set the upper bound to the length of the strings. A random integer between 1 and this upper bound (inclusive) is chosen and as many letters are randomly generated using \int_to_alph:n { \int_rand:n { 26 } }.

With \defrandomstring we can store a random string in a macro. The variant \defrandomstring* doesn't check whether the macro is already defined (use with care).

This works with any engine.

See edit history for a previous version.