This page is an attempt to list some of the most common bashisms ie features not defined by POSIX (ie don't work in dash). It probably won't be exhaustive. Note also we talk about "bashism" because this wiki is largely bash centric but a number of these extensions work in other shells like ksh or zsh.
== Expansions
* Brace Expansion, eg {1..10} is not defined by posix
== Parameter Expansion
list of expansion not defined by posix:
* ${name:n:l} * ${name/ } * ${!name}
== Arrays
* arrays are not defined by posix.
== test
* [[ is not defined by posix * == as an argument of test (aka [) is not defined by posix * < > to compare numbers as argument of test is not defined by posix, though dash implements it * -nt, -ot, -ef are not defined by posix
== Builtins
* echo. posix doesn't define any options, use printf * printf "-v" is not defined by posix. also the %b and %q format are not defined by posix * read, the only option defined by posix is "-r"