CWRU/POSIX.NOTES

   1 Bash POSIX Mode
   2 ===============
   3
   4 Starting Bash with the `--posix' command-line option or executing `set
   5 -o posix' while Bash is running will cause Bash to conform more closely
   6 to the POSIX.2 standard by changing the behavior to match that
   7 specified by POSIX.2 in areas where the Bash default differs.
   8
   9 The following list is what's changed when `POSIX mode' is in effect:
  10
  11   1. When a command in the hash table no longer exists, Bash will
  12      re-search `$PATH' to find the new location.  This is also
  13      available with `shopt -s checkhash'.
  14
  15   2. The `>&' redirection does not redirect stdout and stderr.
  16
  17   3. The message printed by the job control code and builtins when a job
  18      exits with a non-zero status is `Done(status)'.
  19
  20   4. Reserved words may not be aliased.
  21
  22   5. The POSIX.2 `PS1' and `PS2' expansions of `!' to the history
  23      number and `!!' to `!' are enabled, and parameter expansion is
  24      performed on the values of `PS1' and `PS2' regardless of the
  25      setting of the `promptvars' option.
  26
  27   6. Interactive comments are enabled by default.  (Note that Bash has
  28      them on by default anyway.)
  29
  30   7. The POSIX.2 startup files are executed (`$ENV') rather than the
  31      normal Bash files.
  32
  33   8. Tilde expansion is only performed on assignments preceding a
  34      command name, rather than on all assignment statements on the line.
  35
  36   9. The default history file is `~/.sh_history' (this is the default
  37      value of `$HISTFILE').
  38
  39  10. The output of `kill -l' prints all the signal names on a single
  40      line, separated by spaces.
  41
  42  11. Non-interactive shells exit if FILENAME in `.' FILENAME is not
  43      found.
  44
  45  12. Non-interactive shells exit if a syntax error in an arithmetic
  46      expansion results in an invalid expression.
  47
  48  13. Redirection operators do not perform filename expansion on the word
  49      in the redirection unless the shell is interactive.
  50
  51  14. Function names must be valid shell `name's.  That is, they may not
  52      contain characters other than letters, digits, and underscores, and
  53      may not start with a digit.  Declaring a function with an invalid
  54      name causes a fatal syntax error in non-interactive shells.
  55
  56  15. POSIX.2 `special' builtins are found before shell functions during
  57      command lookup.
  58
  59  16. If a POSIX.2 special builtin returns an error status, a
  60      non-interactive shell exits.  The fatal errors are those listed in
  61      the POSIX.2 standard, and include things like passing incorrect
  62      options, redirection errors, variable assignment errors for
  63      assignments preceding the command name, and so on.
  64
  65  17. If the `cd' builtin finds a directory to change to using
  66      `$CDPATH', the value it assigns to the `PWD' variable does not
  67      contain any symbolic links, as if `cd -P' had been executed.
  68
  69  18. If `$CDPATH' is set, the `cd' builtin will not implicitly append
  70      the current directory to it.  This means that `cd' will fail if no
  71      valid directory name can be constructed from any of the entries in
  72      `$CDPATH', even if the a directory with the same name as the name
  73      given as an argument to `cd' exists in the current directory.
  74
  75  19. A non-interactive shell exits with an error status if a variable
  76      assignment error occurs when no command name follows the assignment
  77      statements.  A variable assignment error occurs, for example, when
  78      trying to assign a value to a readonly variable.
  79
  80  20. A non-interactive shell exits with an error status if the iteration
  81      variable in a `for' statement or the selection variable in a
  82      `select' statement is a readonly variable.
  83
  84  21. Process substitution is not available.
  85
  86  22. Assignment statements preceding POSIX.2 special builtins persist
  87      in the shell environment after the builtin completes.
  88
  89  23. The `export' and `readonly' builtin commands display their output
  90      in the format required by POSIX.2.
  91
  92
  93 There is other POSIX.2 behavior that Bash does not implement.
  94 Specifically:
  95
  96   1. Assignment statements affect the execution environment of all
  97      builtins, not just special ones.
  98