COMPAT

   1 This document details the incompatibilites between this version of bash,
   2 bash-2.05, and the previous widely-available version, bash-1.14 (which
   3 is still the `standard' version for many Linux distributions).  These
   4 were discovered by users of bash-2.x, so this list is not comprehensive.
   5
   6 1.  Bash now uses a new quoting syntax, $"...", to do locale-specific
   7     string translation.  Users who have relied on the (undocumented)
   8     behavior of bash-1.14 will have to change their scripts.  For
   9     instance, if you are doing something like this to get the value of
  10     a variable whose name is the value of a second variable:
  11
  12         eval var2=$"$var1"
  13
  14     you will have to change to a different syntax.
  15
  16     This capability is directly supported by bash-2.0:
  17
  18         var2=${!var1}
  19
  20     This alternate syntax will work portably between bash-1.14 and bash-2.0:
  21
  22         eval var2=\$${var1}
  23
  24 2.  One of the bugs fixed in the YACC grammar tightens up the rules
  25     concerning group commands ( {...} ).  The `list' that composes the
  26     body of the group command must be terminated by a newline or
  27     semicolon.  That's because the braces are reserved words, and are
  28     recognized as such only when a reserved word is legal.  This means
  29     that while bash-1.14 accepted shell function definitions like this:
  30
  31         foo() { : }
  32
  33     bash-2.0 requires this:
  34
  35         foo() { :; }
  36
  37     This is also an issue for commands like this:
  38
  39         mkdir dir || { echo 'could not mkdir' ; exit 1; }
  40
  41     The syntax required by bash-2.0 is also accepted by bash-1.14.
  42
  43 3.  The options to `bind' have changed to make them more consistent with
  44     the rest of the bash builtins.  If you are using `bind -d' to list
  45     the readline keybindings in a form that can be re-read, use `bind -p'
  46     instead.  If you were using `bind -v' to list the keybindings, use
  47     `bind -P' instead.
  48
  49 4.  The `long' invocation options must now be prefixed by `--' instead
  50     of `-'.  (The old form is still accepted, for the time being.)
  51
  52 5.  There was a bug in the version of readline distributed with bash-1.14
  53     that caused it to write badly-formatted key bindings when using
  54     `bind -d'.  The only key sequences that were affected are C-\ (which
  55     should appear as \C-\\ in a key binding) and C-" (which should appear
  56     as \C-\").  If these key sequences appear in your inputrc, as, for
  57     example,
  58
  59         "\C-\": self-insert
  60
  61     they will need to be changed to something like the following:
  62
  63         "\C-\\": self-insert
  64
  65 6.  A number of people complained above having to use ESC to terminate an
  66     incremental search, and asked for an alternate mechanism.  Bash-2.03
  67     uses the value of the settable readline variable `isearch-terminators'
  68     to decide which characters should terminate an incremental search.  If
  69     that variable has not been set, ESC and Control-J will terminate a
  70     search.
  71
  72 7.  Some variables have been removed:  MAIL_WARNING, notify, history_control,
  73     command_oriented_history, glob_dot_filenames, allow_null_glob_expansion,
  74     nolinks, hostname_completion_file, noclobber, no_exit_on_failed_exec, and
  75     cdable_vars.  Most of them are now implemented with the new `shopt'
  76     builtin; others were already implemented by `set'.  Here is a list of
  77     correspondences:
  78
  79         MAIL_WARNING                    shopt mailwarn
  80         notify                          set -o notify
  81         history_control                 HISTCONTROL
  82         command_oriented_history        shopt cmdhist
  83         glob_dot_filenames              shopt dotglob
  84         allow_null_glob_expansion       shopt nullglob
  85         nolinks                         set -o physical
  86         hostname_completion_file        HOSTFILE
  87         noclobber                       set -o noclobber
  88         no_exit_on_failed_exec          shopt execfail
  89         cdable_vars                     shopt cdable_vars
  90
  91 8. `ulimit' now sets both hard and soft limits and reports the soft limit
  92     by default (when neither -H nor -S is specified).  This is compatible
  93     with versions of sh and ksh that implement `ulimit'.  The bash-1.14
  94     behavior of, for example,
  95
  96                 ulimit -c 0
  97
  98     can be obtained with
  99
 100                 ulimit -S -c 0
 101
 102     It may be useful to define an alias:
 103
 104                 alias ulimit="ulimit -S"
 105
 106 9.  Bash-2.01 uses a new quoting syntax, $'...' to do ANSI-C string
 107     translation.  Backslash-escaped characters in ... are expanded and
 108     replaced as specified by the ANSI C standard.
 109
 110 10. The sourcing of startup files has changed somewhat.  This is explained
 111     more completely in the INVOCATION section of the manual page.
 112
 113     A non-interactive shell not named `sh' and not in posix mode reads
 114     and executes commands from the file named by $BASH_ENV.  A
 115     non-interactive shell started by `su' and not in posix mode will read
 116     startup files.  No other non-interactive shells read any startup files.
 117
 118     An interactive shell started in posix mode reads and executes commands
 119     from the file named by $ENV.
 120
 121 11. The <> redirection operator was changed to conform to the POSIX.2 spec.
 122     In the absence of any file descriptor specification preceding the `<>',
 123     file descriptor 0 is used.  In bash-1.14, this was the behavior only
 124     when in POSIX mode.  The bash-1.14 behavior may be obtained with
 125
 126         <>filename 1>&0
 127
 128 12. The `alias' builtin now checks for invalid options and takes a `-p'
 129     option to display output in POSIX mode.  If you have old aliases beginning
 130     with `-' or `+', you will have to add the `--' to the alias command
 131     that declares them:
 132
 133         alias -x='chmod a-x' --> alias -- -x='chmod a-x'
 134
 135 13. There was a bug in bash-1.14 and previous versions that caused it to
 136     accept as valid syntax for loops of the form
 137
 138         for f in ; do ... ; done
 139
 140     This should be a syntax error, and bash-2.x treats it as such.
 141
 142 14. The behavior of range specificiers within bracket matching expressions
 143     in the pattern matcher (e.g., [A-Z]) depends on the current locale,
 144     specifically the value of the LC_COLLATE environment variable.  Setting
 145     this variable to C or POSIX will result in the traditional ASCII behavior
 146     for range comparisons.  If the locale is set to something else, e.g.,
 147     en_US (specified by the LANG or LC_ALL variables), collation order is
 148     locale-dependent.  For example, the en_US locale sorts the upper and
 149     lower case letters like this:
 150
 151         AaBb...Zz
 152
 153     so a range specification like [A-Z] will match every letter except `z'.
 154
 155     The portable way to specify upper case letters is [:upper:] instead of
 156     A-Z; lower case may be specified as [:lower:] instead of a-z.
 157
 158     Look at the manual pages for setlocale(3), strcoll(3), and, if it is
 159     present, locale(1).
 160
 161     You can find your current locale information by running locale(1):
 162
 163         caleb.ins.cwru.edu(2)$ locale
 164         LANG=en_US
 165         LC_CTYPE="en_US"
 166         LC_NUMERIC="en_US"
 167         LC_TIME="en_US"
 168         LC_COLLATE="en_US"
 169         LC_MONETARY="en_US"
 170         LC_MESSAGES="en_US"
 171         LC_ALL=en_US
 172
 173     My advice is to put
 174
 175         export LC_COLLATE=C
 176
 177     into /etc/profile and inspect any shell scripts run from cron for
 178     constructs like [A-Z].  This will prevent things like
 179
 180         rm [A-Z]*
 181
 182     from removing every file in the current directory except those beginning
 183     with `z' and still allow individual users to change the collation order.
 184     Users may put the above command into their own profiles as well, of course.
 185
 186 15.  Bash versions up to 1.14.7 included an undocumented `-l' operator to
 187      the `test/[' builtin.  It was a unary operator that expanded to the
 188      length of its string argument.  This let you do things like
 189
 190         test -l $variable -lt 20
 191
 192      for example.
 193
 194      This was included for backwards compatibility with old versions of the
 195      Bourne shell, which did not provide an easy way to obtain the length of
 196      the value of a shell variable.
 197
 198      This operator is not part of the POSIX standard, because one can (and
 199      should) use ${#variable} to get the length of a variable's value.
 200      Bash-2.x does not support it.