Capitalizing in brackets

I would like to know how to capitalize all letter that are placed in these kind of brackets:
[]

What I have now is

Replace with regular expression
Field: TITLE
Regular expression: [(.{1})]
Replace matches with: [$upper($0)]

but that doesn't work

Please note, that the code would have to start executing itself after seeing the opening, and stop after the closing ] - it can't just start and run to the end of tag field

You may try:
$regexp(%title%,'([.*])',\U$1)
in a format value action.
Set the correct fieldname in the regexp()

Proposals for changing ... Tag-Field: TITLE From : Ab[c de fg]hi To : Ab[C DE FG]hi Action: Replace with Regular Expression Field : TITLE Regular Expression : \[.+?\] Replace matches with: \U$0 ... or ... Action: Replace with Regular Expression Field : TITLE Regular Expression : \[.+?\] Replace matches with: $upper($0) ... or ... Action: Format value Field : TITLE Formatstring: $regexp(%TITLE%,'\[.+?\]','\U$0') ... or ... experimental ... Note: Part '[xxx]' must be embedded in text string. Action: Format value Field : TITLE Formatstring: $replace(%TITLE%,'[','\\\\',']','\\\\') Action: Format value Field : TITLE Formatstring: $meta(TITLE,0)'['$upper($meta(TITLE,1))']'$meta(TITLE,2)

DD.20150709.1914.CEST

Thise seems to do the trick

Thank you both