Quote:
The "-a" operator also doesn't work:
if [ $STATUS -ne 200 ] -a [[ "$STRING" != "$VALUE" ]]
For a more elaborate explanation: [ and ] are not Bash reserved words. The if keyword introduces a conditional to be evaluated by a job (the conditional is true if the job's return value is 0 or false otherwise).
For trivial tests, there is the test program (man test).
As some find lines like if test -f filename; then foo bar; fi, etc. annoying, on most systems you find a program called [ which is in fact only a symlink to the test program. When test is called as [, you have to add ] as the last positional argument.
So if test -f filename is basically the same (in terms of processes spawned) as if [ -f filename ]. In both cases the test program will be started, and both processes should behave identically.
Here's your mistake: if [ $STATUS -ne 200 ] -a [[ "$STRING" != "$VALUE" ]] will parse to if + some job, the job being everything except the if itself. The job is only a simple command (Bash speak for something which results in a single process), which means the first word ([) is the command and the rest its positional arguments. There are remaining arguments after the first ].
Also not, [[ is indeed a Bash keyword, but in this case it's only parsed as a normal command argument, because it's not at the front of the command.