Return last item of strings.Split() slice in Golang

Question

I am splitting file names in Go to get at the file extension (e.g. import ("strings") ; strings.Split("example.txt", ".")). For this reason, I would like to return the last item in the slice returned by the split, i.e.

for strings.Split("ex.txt", "."), I want txt

This question suggests that doing

strings.Split("ex.txt", ".")[len(strings.Split("ex.txt", ".")) - 1]

is the only way to get at it. That is, there is no -1 as in Python. This seems very wasteful to me, as I feel we are doing the same splitting operation twice.

Is there no better command for getting the last item of a slice in Go?
If no, would the best approach be to write the result of Split into a variable, or just do the above?

... another approach: `"ex.txt"[strings.LastIndex("ex.txt", ".")+1:]`, but still, please use a variable for the string because this is ugly. — mkopriva, May 12 '18 at 22:49

score 50 · Answer 1 · answered Apr 10 '19 at 16:07

50

strings.LastIndex makes this quite neat:

s := "Hello,Stack,Overflow"
last := s[strings.LastIndex(s, ",")+1:]
fmt.Println(last)

returns "Overflow". If the search string isn't found it returns the whole string, which is logical.

Playground here

answered Apr 10 '19 at 16:07

Jon Egerton

40,401
11
97
129

score 30 · Accepted Answer · edited Apr 17 '20 at 09:48

You should assign the results of the split to a variable, instead of calling it twice.

ss := strings.Split(msg, ".")
s := ss[len(ss)-1]

(Notice that this allows (or maybe forces) you to deal with the case where ss is empty or something else unexpected explicitly, before indexing it.)

If you're doing this over and over again, and it offends you having to use two lines (or two lines plus error handling) instead of one, you can abstract it into a function easily:

func lastString(ss []string) string {
    return ss[len(ss)-1]
}

s1 := lastString(strings.Split("example.txt", "."))
s2 := lastString(strings.Split("example.jpg", "."))

After all, passing the result of a function as an argument has essentially the same effect as binding it to a variable.

score 7 · Answer 3 · answered May 12 '18 at 22:53

7

I would use the filepath package rather than parsing it yourself:

import "path/filepath"

s := "file.ext"
ext := filepath.Ext(s)
if len(ext) != 0 {
    fmt.Printf("ext = %s\n", ext[1:])
} else {
    fmt.Printf("no ext\n")
}

This will work with a full path as well as just a file name.

answered May 12 '18 at 22:53

hc6

153
9

1

Thank you! I saw that package but wanted to do it by hand for this purpose. – patrick May 12 '18 at 22:57

score 1 · Answer 4 · answered Jun 03 '23 at 09:47

1

Simpler is to "delete" everything up to and including the (last) dot:

extension := regex.MustCompile(`.*\.`).ReplaceAllString("ex.txt", "")

answered Jun 03 '23 at 09:47

Bohemian

412,405
93
575
722

Return last item of strings.Split() slice in Golang

4 Answers4