How to extract comma separated substrings from a string?

Question

Need to parse the algorithms separated by comma in group.

SSH Enabled - version 2.0
Authentication methods:publickey,keyboard-interactive,password
Encryption Algorithms:aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc
MAC Algorithms:hmac-sha1,hmac-sha1-96
Authentication timeout: 120 secs; Authentication retries: 3
Minimum expected Diffie Hellman key size : 1024 bits
IOS Keys in SECSH format(ssh-rsa, base64 encoded):

I have tried to separate them with comma but not getting the expected results:

^Encryption Algorithms:(.*?)(?:,|$)

Expected results is to have each algorithm in group 1 with no empty group

aes128-ctr
aes192-ctr
aes256-ctr
aes128-cbc
3des-cbc
aes192-cbc
aes256-cbc

Answer 1

It may not be the best way, however it might be one way to split our string into three parts, maybe even before running it through RegEx engine. If that would not be the case and we wish to have an expression, this might be close:

(.+Encryption Algorithms:)|([a-z0-9-]+)(?:,|\s)|(MAC.+)

---

If you also have new lines, you might want to test with other expressions, maybe similar to:

([\s\S]+Encryption Algorithms:)|([a-z0-9-]+)(?:,|\s)|(MAC[\s\S]+)

---

([\w\W]+Encryption Algorithms:)|([a-z0-9-]+)(?:,|\s)|(MAC[\w\W]+)

---

([\d\D]+Encryption Algorithms:)|([a-z0-9-]+)(?:,|\s)|(MAC[\d\D]+)

Demo 1

Demo 2

RegEx

If this expression wasn't desired, it can be modified or changed in regex101.com.

RegEx Circuit

jex.im visualizes regular expressions:

Test

# coding=utf8
# the above tag defines encoding for this document and is for Python 2.x compatibility

import re

regex = r"([\w\W]+Encryption Algorithms:)|([a-z0-9-]+)(?:,|\s)|(MAC[[\w\W]+)"

test_str = ("SSH Enabled - version 2.0\n"
    "Authentication methods:publickey,keyboard-interactive,password\n"
    "Encryption Algorithms:aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc\n"
    "MAC Algorithms:hmac-sha1,hmac-sha1-96\n"
    "Authentication timeout: 120 secs; Authentication retries: 3\n"
    "Minimum expected Diffie Hellman key size : 1024 bits\n"
    "IOS Keys in SECSH format(ssh-rsa, base64 encoded):\n")

subst = "\\2 "

# You can manually specify the number of replacements by changing the 4th argument
result = re.sub(regex, subst, test_str, 0, re.MULTILINE)

if result:
    print (result)

# Note: for Python 2.7 compatibility, use ur"" to prefix the regex and u"" to prefix the test string and substitution.

Demo

const regex = /(.+Encryption Algorithms:)|([a-z0-9-]+)(?:,|\s)|(MAC.+)/gm;
const str = `SSH Enabled - version 2.0 Authentication methods:publickey,keyboard-interactive,password Encryption Algorithms:aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc MAC Algorithms:hmac-sha1,hmac-sha1-96 Authentication timeout: 120 secs; Authentication retries: 3 Minimum expected Diffie Hellman key size : 1024 bits IOS Keys in SECSH format(ssh-rsa, base64 encoded):`;
const subst = `$2 `;

// The substituted value will be contained in the result variable
const result = str.replace(regex, subst);

console.log('Substitution result: ', result);

Answer 2

Another way could be to match the string starting with Encryption Algorithms:, and then capture in a group a repeating pattern that matches the part with the hyphen and repeats that with a comma prepended.

If there is a match, you could split the first capturing group on a comma.

^Encryption Algorithms:(\w+-\w+(?:,\w+-\w+)*)

Explanation

• ^
• Encryption Algorithms:
• ( Start capturing group
  • \w+-\w+ Match 1+ word chars, - and 1+ word chars
  • (?:,\w+-\w+)* 0+ times repeat a comma followed by 1+ word chars, - and 1+ word chars
• ) Close capturing group

Regex demo | Python demo

import re
regex = r"^Encryption Algorithms:(\w+-\w+(?:,\w+-\w+)*)"
test_str = ("SSH Enabled - version 2.0\n"
            "Authentication methods:publickey,keyboard-interactive,password\n"
            "Encryption Algorithms:aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc\n"
            "MAC Algorithms:hmac-sha1,hmac-sha1-96\n"
            "Authentication timeout: 120 secs; Authentication retries: 3\n"
            "Minimum expected Diffie Hellman key size : 1024 bits\n"
            "IOS Keys in SECSH format(ssh-rsa, base64 encoded):")

matches = re.search(regex, test_str, re.MULTILINE)
if matches:
    print(matches.group(1).split(","))

Result:

['aes128-ctr', 'aes192-ctr', 'aes256-ctr', 'aes128-cbc', '3des-cbc', 'aes192-cbc', 'aes256-cbc']