20. posix special builtins are found before shell functions during command lookup.
21. The time reserved word may be used by itself as a command. When used in this way, it displays timing statistics for the shell and its completed children. The TIMEFORMAT variable controls the format of the timing information.
22. When parsing and expanding a ${. . . } expansion that appears within double quotes, single quotes are no longer special and cannot be used to quote a closing brace or other special character, unless the operator is one of those defined to perform pattern removal. In this case, they do not have to appear as matched pairs.
23. The parser does not recognize time as a reserved word if the next token begins with a
‘-’.
24. If a posix special builtin returns an error status, a non-interactive shell exits. The fatal errors are those listed in the posix standard, and include things like passing incorrect options, redirection errors, variable assignment errors for assignments preceding the command name, and so on.
25. A non-interactive shell exits with an error status if a variable assignment error occurs when no command name follows the assignment statements. A variable assignment error occurs, for example, when trying to assign a value to a readonly variable.
26. A non-interactive shell exits with an error status if a variable assignment error occurs in an assignment statement preceding a special builtin, but not with any other simple command.
27. A non-interactive shell exits with an error status if the iteration variable in a for statement or the selection variable in a select statement is a readonly variable.
28. Process substitution is not available.
29. While variable indirection is available, it may not be applied to the ‘#’ and ‘?’ special parameters.
30. Assignment statements preceding posix special builtins persist in the shell environment after the builtin completes.
31. Assignment statements preceding shell function calls persist in the shell environment after the function returns, as if a posix special builtin command had been executed.
32. The export and readonly builtin commands display their output in the format re- quired by posix.
33. The trap builtin displays signal names without the leading SIG.
34. The trap builtin doesn’t check the first argument for a possible signal specification and revert the signal handling to the original disposition if it is, unless that argument consists solely of digits and is a valid signal number. If users want to reset the handler for a given signal to the original disposition, they should use ‘-’ as the first argument.
35. The . and source builtins do not search the current directory for the filename argument if it is not found by searching PATH.
36. Subshells spawned to execute command substitutions inherit the value of the -e option from the parent shell. When not in posix mode, Bash clears the -e option in such subshells.
37. Alias expansion is always enabled, even in non-interactive shells.
38. When the alias builtin displays alias definitions, it does not display them with a leading ‘alias ’ unless the -p option is supplied.