`${PARAMETER:OFFSET}' does not work for negative offset

[Ulrich Windl]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc -I/home/abuild/rpmbuild/BUILD/bash-4.2 
-L/home/abuild/rpmbuild/BUILD/bash-4.2/../readline-6.2
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' 
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-suse-linux-gnu' 
-DCONF_VENDOR='suse' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL 
-DHAVE_CONFIG_H   -I.  -I. -I./include -I./lib   -fmessage-length=0 
-grecord-gcc-switches -O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector 
-funwind-tables -fasynchronous-unwind-tables -g  -D_GNU_SOURCE -DRECYCLES_PIDS 
-Wall -g -Wuninitialized -Wextra -Wno-unprototyped-calls -Wno-switch-enum 
-Wno-unused-variable -Wno-unused-parameter -ftree-loop-linear -pipe 
-DBNC382214=0 -fprofile-use
uname output: Linux pc 4.1.15-8-default #1 SMP PREEMPT Wed Jan 20 16:41:00 UTC 
2016 (0e3b3ab) x86_64 x86_64 x86_64 GNU/Linux
Machine Type: x86_64-suse-linux-gnu

Bash Version: 4.2
Patch Level: 47
Release Status: release

Description:
    `${PARAMETER:OFFSET}' does not work for negative offset; the complete
    parameter value is substituted

    The bug goes back to at least bash 3.2...

Repeat-By:
    "X=ABC; echo ${X:-2}" outputs "ABC", and not "BC"

Fix:
    Ugly:
    (( Y = ${#X} - 2 ))
    echo ${X:$Y}

    or shorter:
    echo ${X:$((${#X}-2))}