RegExp.md

Regular Expressions

---

Or

grep "47.135.152.["22""50"]" <file>
47.135.152.22
47.135.152.50

Repetition - match preceding token

? → optional

* → 0 or more

+ → 1 or more

grep "CSeq: [0-9]* SUBSCRIBE" 

Backreference - repeat a capturing group.

e.g. AWS Cognito URL must have "Region" twice, Java:

// Note: The "\\1" part is the back-reference to the Region in the 
// endpoint domain name.  They must be the same.
// For example: https://cognito-idp.us-east-1.amazonaws.com/us-east-1_fgTHwGEfw
private static final Pattern COGNITO_ISSUER_URL_RE = Pattern
      .compile("https://cognito-idp\\.([a-z0-9-]+)\\.amazonaws.com/\\1_[A-Za-z0-9]+");

return COGNITO_ISSUER_URL_RE.matcher(issuer).matches();

Examples

MAC (Media Access Control) filename (without : or -)

ls . |  grep -E "^[0-9a-fA-F]{12}$"

The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line.