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How to check if a string s1 is a substring of another string s2?

For example (test-substring "f t" "df tj") --> t, (test-substring "ft" "df tj") --> nil.

29

The standard Emacs Lisp approach is regular expression matching:

(string-match-p (regexp-quote needle) haystack)
11

cl-search can do that (and also returns the index of the substring, if found):

ELISP> (cl-search "f t" "df tj")
1 (#o1, #x1, ?\C-a)
ELISP> (cl-search "ft" "df tj")
nil

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