BASH gotchas - Episode 0

Extracting substrings

a="abcdefghi"
echo ${a}
echo ${a:5:2}
echo ${a:8:4}
# ${variable_name:0-based index:length}

Default value for variables

a="abcdefghi"
echo ${a:-foobar}
echo ${b:-foobar}
echo ${c:-${b:-foobar}}
# ${variable_name:-default_expression}