${variable: ±substring}
${variable#prefixe_a_supprimer}
${variable/search/replace}
${variable//search/replaceall}
var=poete
echo ${var: -1} # affiche "e"
echo ${var: +1} # affiche "p"
echo ${var%te} # affiche "poe"
echo ${var#po} # affiche "ete"
echo ${var/t/m} # affiche "poeme"
echo ${var//e/3} # affiche "po3t3"