Golang: extract data with Regex

Question

I'm trying to extract whatever data inside ${}.

For example, the data extracted from this string should be abc.

git commit -m '${abc}'

Here is the actual code:

re := regexp.MustCompile("${*}")
match := re.FindStringSubmatch(command)

But that doesn't work, any idea?

score 56 · Accepted Answer · edited Sep 07 '22 at 19:29

56

In regex, $, { and } have special meaning

$ <-- End of string
{} <-- Contains the range. e.g. a{1,2}

So you need to escape them in the regex. Because of things like this, it is best to use raw string literals when working with regular expressions:

re := regexp.MustCompile(`\$\{([^}]*)\}`)
match := re.FindStringSubmatch("git commit -m '${abc}'")
fmt.Println(match[1])

Golang Demo

With double quotes (interpreted string literals) you need to also escape the backslashes:

re := regexp.MustCompile("\\$\\{(.*?)\\}")

edited Sep 07 '22 at 19:29

Old Pro

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answered May 19 '16 at 07:44

rock321987

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A hint: using raw string literals to define a regex pattern is advisable. E.g. [`re := regexp.MustCompile(\`\$\{(.*?)\}\`)`](https://play.golang.org/p/jK5TSUGCxt) – Wiktor Stribiżew May 19 '16 at 08:17
@WiktorStribiżew its already in another answer..so i didn't updated mine – rock321987 May 19 '16 at 08:18
1

The other answer is not correct, I think. `+?` and `*?` are different quantifiers. In regex, every symbol matters and can change the output greatly. – Wiktor Stribiżew May 19 '16 at 08:19

score 4 · Answer 2 · answered May 19 '16 at 07:42

4

Try re := regexp.MustCompile(\$\{(.*)\}) * is a quantifier, you need something to quantify. . would do as it matches everything.

answered May 19 '16 at 07:42

Hermes Martinez

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`.*` is a greedy subpattern and can overfire. Use with caution. It might work only with the current example, but not in real life scenario. – Wiktor Stribiżew May 19 '16 at 08:19
1

I didn't say it wasn't, he wanted to know why his expression didn't work, I told him why. – Hermes Martinez May 19 '16 at 08:20

score 2 · Answer 3 · answered Sep 22 '20 at 07:43

You can try with this too,

re := regexp.MustCompile("\\$\\{(.*?)\\}")

str := "git commit -m '${abc}'"
res := re.FindAllStringSubmatch(str, 1)
for i := range res {
    //like Java: match.group(1)
    fmt.Println("Message :", res[i][1])
}

GoPlay: https://play.golang.org/p/PFH2oDzNIEi

score 1 · Answer 4 · answered Apr 12 '21 at 03:20

For another approach, you can use os.Expand:

package main
import "os"

func main() {
   command := "git commit -m '${abc}'"
   var match string
   os.Expand(command, func(s string) string {
      match = s
      return ""
   })
   println(match == "abc")
}

https://golang.org/pkg/os#Expand

score 0 · Answer 5 · answered May 19 '16 at 07:43

0

Because $, { and } all have special meaning in a regex and need to be backslashed to match those literal characters, because * doesn't work that way, and because you didn't actually include a capturing group for the data you want to capture. Try:

re := regexp.MustCompile(`\$\{.+?)\}`)

answered May 19 '16 at 07:43

hobbs

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The `*` in the OP pattern makes me think that the string inside `{}` can be empty. Thus, rock's answer seems to be closer to what OP needs. – Wiktor Stribiżew May 19 '16 at 08:18

score 0 · Answer 6 · answered May 09 '23 at 22:17

You can use named group to extract the value of a string.

import (
    "fmt"
    "regexp"
)

func main() {
    command := "git commit -m '${abc}'"

    r := regexp.MustCompile(`\$\{(?P<text>\w+)\}`)
    subMatch := r.FindStringSubmatch(command)

    fmt.Printf("text : %s", subMatch[1])
}

GoPlay

Golang: extract data with Regex

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