test="my name is gaole"
echo ${#test} #get length of a string
echo ${test:4} #get substring from 5 to the end
echo ${test:4:6} #get substring from 5 to the following 6 characters
echo ${test:-3} #get the last character,but some bash can't support -3
echo ${test:5:-1} #get substring from 6 and delete the last letter,but some bash can't support
test2="abdabdfebabdABDe"
echo ${test2//b/x} #replace all gs with a
echo ${test2/b/x} #replace the first g
echo ${test2%%*ABDe} #replace from right with
echo ${test2%*ABDe} #replace from right with the shortest length
echo ${test2#abd*d} #replace from left with the shortest length
echo ${test2##abd*d} #replace from left with the largest length
a="test121212121212121212121212"
b="test1"
if [ "test" == "test1" ] ;then #space must be write between every [ and ==
echo "equal"
elif [[ $a == $b* ]] ;then #double zhong kuohao will enable moshi match
echo "contain"
else
echo "not equal"
fi
