${var#prefixo}
It gnaws at the start of the value: # takes the smallest bite, ## the largest.
The hash after the name cuts from the start of the value whatever matches the pattern: # removes the shortest match, ## the longest. The pattern uses glob wildcards, not regular expressions.
The celebrated use is ${caminho##*/}: it eats everything up to the last slash and the file name remains — a basename with no new process.
$ caminho=/var/log/colmeia/acesso.log
$ echo ${caminho#*/}
var/log/colmeia/acesso.log
$ echo ${caminho##*/}
acesso.log