On Sat, Sep 06, 2025 at 23:10:28 -0500, Eric Pruitt wrote:
> I've never read the Bash documentation cover-to-cover. I've been using
> "^^" and ",," for years without being aware they were undocumented
> because I had seen them used elsewhere, and it never crossed my mind
> that they might be undocumented. I'm sure other people also fall into
> this camp.
^^ and ,, are documented. In fact, it's *really* easy to find it,
because you just have to search for ,, and there are no false positives
in the way.
${parameter^pattern}
${parameter^^pattern}
${parameter,pattern}
${parameter,,pattern}
Case modification. This expansion modifies the case of alpha‐
betic characters in parameter. [...]
The undocumented syntax is ~ ~~ which does case flipping like vi's ~
command. That's what this thread has been talking about.
hobbit:~$ x='Hello World'; echo "${x~}"
hello World
hobbit:~$ x='Hello World'; echo "${x~~}"
hELLO wORLD
hobbit:~$ x='Hello World'; echo "${x~~[AaEeIiOoUu]}"
HEllO WOrld
Nobody has shown a real-world use case for this yet.
