How can I get a substring of a string in Emacs Lisp?

Question

When I have a string like "Test.m", how can I get just the substring "Test" from that via elisp? I'm trying to use this in my .emacs file.

Answer 1

One way is to use substring (or substring-no-properties):

(substring "Test.m" 0 -2) => "Test"

(substring STRING FROM &optional TO )

Return a new string whose contents are a substring of STRING. The returned string consists of the characters between index FROM (inclusive) and index TO (exclusive) of STRING. FROM and TO are zero-indexed: 0 means the first character of STRING. Negative values are counted from the end of STRING. If TO is nil, the substring runs to the end of STRING.

Answer 2

Stefan's answer is idiomatic, when you just need a filename without extension. However, if you manipulate files and filepaths heavily in your code, i recommend installing Johan Andersson's f.el file and directory API, because it provides many functions absent in Emacs with a consistent API. Check out functions f-base and f-no-ext:

(f-base "~/doc/index.org") ; => "index"
(f-no-ext "~/doc/index.org") ; => "~/doc/index"

If, instead, you work with strings often, install Magnar Sveen's s.el for the same reasons. You might be interested in s-chop-suffix:

(s-chop-suffix ".org" "~/doc/index.org") ; => "~/doc/index"

For generic substring retrieval use dkim's answer.