Replace UTF-8 characters with shell perl

Use this :

 $ echo 'ABCæøåDEF' |
    perl -CSD -Mutf8 -pe 's/([æøå])/[$1]/g'

Works also for files

Output :

ABC[æ][ø][å]DEF

Note :

• substitutions: \\1 is for awk, \1 is for sed and in perl we use $1
• check perldoc perlrun for -CSD utf8 tricks