CWRU/POSIX.NOTES.old

   1 Starting bash with the `--posix' command-line option or executing
   2 `set -o posix' while bash is running will cause bash to conform more
   3 closely to the Posix.2 standard by changing the behavior to match that
   4 specified by Posix.2 in areas where the bash default differs.
   5
   6 The following list is what's changed when `posix mode' is in effect:
   7
   8 1.  When a command in the hash table no longer exists, bash will re-search
   9     $PATH to find the new location.  This is also available with
  10     `shopt -s checkhash'.
  11
  12 2.  The >& redirection does not redirect stdout and stderr.
  13
  14 3.  The message printed by the job control code and builtins when a job
  15     exits with a non-zero status is `Done(status)'.
  16
  17 4.  Reserved words may not be aliased.
  18
  19 5.  The Posix.2 PS1 and PS2 expansions of `!' -> history number and
  20     `!!' -> `!' are enabled, and parameter expansion is performed on
  21     the value regardless of the setting of the `promptvars' option.
  22
  23 6.  Interactive comments are enabled by default.  (Note that bash has
  24     them on by default anyway.)
  25
  26 7.  The Posix.2 startup files are executed ($ENV) rather than the normal
  27     bash files.
  28
  29 8.  Tilde expansion is only performed on assignments preceding a command
  30     name, rather than on all assignment statements on the line.
  31
  32 9.  The default history file is ~/.sh_history (default value of $HISTFILE).
  33
  34 10. The output of `kill -l' prints all the signal names on a single line,
  35     separated by spaces.
  36
  37 11. Non-interactive shells exit if `file' in `. file' is not found.
  38
  39 12. Redirection operators do not perform pathname expansion on the word
  40     in the redirection unless the shell is interactive
  41
  42 13. Function names must be valid shell identifiers.  That is, they may not
  43     contain characters other than letters, digits, and underscores, and
  44     may not start with a digit.  Declaring a function with an illegal name
  45     causes a fatal syntax error in non-interactive shells.
  46
  47 14. Posix.2 `special' builtins are found before shell functions during command
  48     lookup.
  49
  50 15. If a Posix.2 special builtin returns an error status, a non-interactive
  51     shell exits.  The fatal errors are those listed in the POSIX.2 standard,
  52     and include things like passing incorrect options, redirection errors,
  53     variable assignment errors for assignments preceding the command name,
  54     and so on.
  55
  56 16. The environment passed to executed commands is not sorted.  Neither is
  57     the output of `set'.  This is not strictly Posix.2 behavior, but sh
  58     does it this way.  Ksh does not.  It's not necessary to sort the
  59     environment; no program should rely on it being sorted.
  60
  61 17. If the `cd' builtin finds a directory to change to using $CDPATH, the
  62     value it assigns to $PWD does not contain any symbolic links, as if
  63     `cd -P' had been executed.
  64
  65 18. A non-interactive shell exits with an error status if a variable
  66     assignment error occurs when no command name follows the assignment
  67     statements.  A variable assignment error occurs, for example, when
  68     trying to assign a value to a read-only variable.
  69
  70 19. A non-interactive shell exits with an error status if the iteration
  71     variable in a for statement or the selection variable in a select
  72     statement is a read-only variable.
  73
  74 20. Process substitution is not available.
  75
  76 21. Assignment statements preceding POSIX.2 `special' builtins persist in
  77     the shell environment after the builtin completes.
  78
  79 There is other Posix.2 behavior that bash does not implement.  Specifically:
  80
  81 1.  Assignment statements affect the execution environment of all builtins,
  82     not just special ones.