Shell script substring from first indexof substring

Question

I want to accomplish the equivalent of the following pseudo-code in bash (both a and b are inputs to my script) :

String a = "some long string";
String b = "ri";
print (a.substring(a.firstIndexOf(b), a.length()); //prints 'ring'

How can I do this in shell script?

Solution 1

You can do:

$ a="some long string"
$ b="ri"
$ echo $a | grep -o "$b.*"
ring

Solution 2

Try:

    $ a="some long string"
    $ b="ri"

    $ echo ${a/*$b/$b}
    ring

    $ echo ${a/$b*/$b}
    some long stri

Solution 3

Try this:

a="some long string"
b="ri"

echo  ${b}${a#*${b}}

Solution 4

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"

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Comments

[Idemax]

not index of but the string itself and pops error if not find

[tripleee]

Clever. You should double-quote the argument to echo, though.

[Gudlaugur Egilsson]

This is a greedy match, so if there is a second "ri", this prints until and from the second match, not the first.