The bug has been opened on https://bugs.launchpad.net/bugs/196785

"Gedit's syntax highlighting for 'sh' actually is for bash.

Functions and arrays are not valid Bourne shell, and scripts starting with '/bin/sh' which use these will fail on:
* Bourne shell (/bin/sh)
* Bash version 3 and later on many systems, depending on the compile time options of bash. If bash version 3's default POSIX compatibility has been disabled, the behavior may be demonstrated using 'bash --posix file.sh'

Simple fix: mark the syntax highlighting currently labeled as 'sh' as being 'bash'.

Extended fix: include an actual Bourne shell syntax highlighting mode, which marks invalid bourne shell syntax in red.

http://launchpadlibrarian.net/12344708/sh_arrays.sh
sh_arrays.sh (1.8 KiB, text/x-sh)

Here's a cheesy example from Advanced Bash Scripting Guide

Gedit hightlights both the same even though the array syntax is illegal in normal Bourne shell (sh) programming.

Here are the results:

tgalati4@minty5:~/Projects$ ./bash_arrays.sh
area[11] = 23
area[13] = 37
Contents of area[51] are UFOs.
area[43] =
(area[43] unassigned)

area[5] = area[11] + area[13]
area[5] = 60
expr: non-numeric argument
area[6] = area[11] + area[51]
area[6] =

area2[0] = zero
area2[1] = one

area3[17] = seventeen
area3[24] = twenty-four
tgalati4@minty5:~/Projects$ ./sh_arrays.sh
./sh_arrays.sh: 4: area[11]=23: not found
./sh_arrays.sh: 5: area[13]=37: not found
./sh_arrays.sh: 6: area[51]=UFOs: not found
area[11] = ./sh_arrays.sh: 17: Syntax error: Bad substitution

http://launchpadlibrarian.net/12344712/bash_arrays.sh
bash_arrays.sh (1.8 KiB, text/x-sh)

bash_arrays.sh attached."