Since I'm unable to submit a bug via bugs.busybox.net due to some
certificate error, I'm posting it here:
When offset is a literal negative the variable produces and error "bad
substitution" when issuing the proper form with a space after for the first
: in ${parameter:offset:length} for a negative number. See
https://www.gnu.org/software/bash/manual/bashref.html#Shell-Parameter-Expansion
subsection on ${parameter:offset:length}
It should be noted that this does work when the offset parameter is a
variable instead of a literal with a negative number. The script below
reproduces the issue and showcases the operation with a variable offset vs
a value offset.
#!./busybox bash
set -x
parameter=abcdef
offset=2
noffset=-2
echo "parametert '${parameter}'"
echo "var offset '${parameter:${offset}}'"
echo "var noffset '${parameter:${noffset}}'"
echo "val 2 '${parameter:2}'"
echo "val -2 (bad form) '${parameter:-2}'"
echo "val -2 (good form) '${parameter: -2}'"
#EOF
With this script busybox bash gives the following output:
~/project/busybox $ ./test.sh
+ parameter=abcdef
+ offset=2
+ noffset=-2
+ echo parametert 'abcdef'
parametert 'abcdef'
+ echo var offset 'cdef'
var offset 'cdef'
+ echo var noffset 'ef'
var noffset 'ef'
+ echo val 2 'cdef'
val 2 'cdef'
+ echo val -2 (bad form) 'abcdef'
val -2 (bad form) 'abcdef'
./test.sh: line 13: syntax error: bad substitution
~/project/busybox $
Changing the script to use the Linux Bash:
jim@jim-VirtualBox:~/project/busybox$ ./test.sh
+ parameter=abcdef
+ offset=2
+ noffset=-2
+ echo 'parametert '\''abcdef'\'''
parametert 'abcdef'
+ echo 'var offset '\''cdef'\'''
var offset 'cdef'
+ echo 'var noffset '\''ef'\'''
var noffset 'ef'
+ echo 'val 2 '\''cdef'\'''
val 2 'cdef'
+ echo 'val -2 (bad form) '\''abcdef'\'''
val -2 (bad form) 'abcdef'
+ echo 'val -2 (good form) '\''ef'\'''
val -2 (good form) 'ef'
jim@jim-VirtualBox:~/project/busybox$
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