Pesquisando - poucos links:
- Adicione recursivamente a extensão do arquivo a todos os arquivos - Stack Overflow
- Adicionar extensão de arquivo a arquivos com o bash - Stack Overflow
homem renomear:
NAME
rename - renames multiple files
SYNOPSIS
rename [ -v ] [ -n ] [ -f ] perlexpr [ files ]
DESCRIPTION
"rename" renames the filenames supplied according to the rule specified as
the first argument. The perlexpr argument is a Perl expression which is
expected to modify the $_ string in Perl for at least some of the filenames
specified. If a given filename is not modified by the expression, it will not
be renamed. If no filenames are given on the command line, filenames will be
read via standard input...
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