In bash, what's the diff between [[ test1 && test2 ]] vs [[ test1 ]] && [[ test2 ]]

Question

What's the difference, if any, in the following two bash evaluations:

if [[ -s $file1 && $file1 -nt $file2 ]]; then

if [[ -s $file1 ]] && [[ $file1 -nt $file2 ]]; then

Answer 1

There is no difference. They're functionally identical.

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An interesting aside, if you used [ instead of [[, there actually is a detectable difference cause by the order of evaluation:

[ -s "$file1" -a "$file1" -nt "$(echo side effect >&2)" ] 

[ -s "$file1" ] && [ "$file1" -nt "$(echo side effect >&2)" ] 

In this case, the first line would print "side effect" while the second would not.

Again, however, this is only the case for [ and not for [[ ]].