i [[ daily , never had such.. sounds like u dont type in C in utf8 On Thu, Feb 23, 2023, 9:58 AM Qingsheng Huang <huangq...@126.com> wrote:
> Here shows the behavious of empty conditional expressions: > > ------------------------------------------------------------------------ > infinite:~# [[ ]] > -bash: syntax error near unexpected token `]]' > infinite:~# [[ ]] > infinite:~# [[ "$A" ]] > -bash: syntax error near unexpected token `"$A"' > infinite:~# [[ "$A" ]] > infinite:~# [[ "$A" ]] > infinite:~# [[ ]] > infinite:~# [[ "$A" ]] > -bash: syntax error near unexpected token `"$A"' > infinite:~# echo $? > 2 > infinite:~# [[ "$A" ]] > infinite:~# echo $? > 1 > infinite:~# > infinite:~# bash --version > bash --version > GNU bash, version 5.2.15(1)-release (x86_64-pc-linux-gnu) > ------------------------------------------------------------------------ > > The variable $A has never been defined. > Double brackets surrounding 1) a few spaces or 2) an empty variable even > quoted behave illogically. I've also try different lengths of spaces, and > also an empty variable without quotes, the same illogical. > > I am curious if I am the first guy encounter such a situation. > My observation: > 1) An empty conditional expression will first triger an syntax error, > return > with code 2; > 2) Immediate another empty conditional expression won't triger such an > error, > return with code 1; > 3) Subsequent a conditional expression with empty variables will triger the > error again; > 4) The same conditional expression won't triger the error until different > commands are input; > > I guess it has something to do with the cache of command evaluation. > It seems there is a counter recording some state. I hope my guess may help > in debugging. > > According to the manual, I think an empty condition like ``[[ ]]'' and > ``[[ $EMPTY ]]'' should always triger syntax error, but a condition with > an empty string like ``[[ "" ]]'' and ``[[ "$EMPTY" ]]'' should evaluate > to false or return 1. >
