Shell Variable Substitutions

Variable substitutions apply a pattern to the content of a variable either from the left
or right side. The following list contains the possible syntax forms:

${VAR#pattern}
removes the shortest possible match from the left:
file=/home/tux/book/book.tar.bz2
echo ${file#*/}
home/tux/book/book.tar.bz2

${VAR##pattern}
removes the longest possible match from the left:
file=/home/tux/book/book.tar.bz2
echo ${file##*/}
book.tar.bz2

${VAR%pattern}
removes the shortest possible match from the right:
file=/home/tux/book/book.tar.bz2
echo ${file%.*}
/home/tux/book/book.tar

${VAR%%pattern}
removes the longest possible match from the right:
file=/home/tux/book/book.tar.bz2
echo ${file%%.*}
/home/tux/book/book

${VAR/pattern_1/pattern_2}
substitutes the content of VAR from the pattern_1 with pattern_2:
file=/home/tux/book/book.tar.bz2
echo ${file/tux/wilber}
/home/wilber/book/book.tar.bz2