Shell script substring from first indexof substring
grep, sed and so on can be used but it is not pure-bash.
expr is a good choice but index parameter is not, because it matches character not the whole string, try with a = "some wrong string" it matches the first r.
Instead use expr match with its regular expression parameter :
a="some long string";b="ri";echo ${a:$(expr match "$a" ".*${b}") - $(expr length "$b")}It also works with a = "some wrong string"