CODEWITHSUNDEEP
regex
Juan
Juan

Reputation: 15715

Regex to match only the first line?

Is it possible to make a regex match only the first line of a text? So if I have the text:

This is the first line.
This is the second line. ...

It would match "This is the first line.", whatever the first line is.

Upvotes: 32

Views: 79153

Answers (4)

Paweł Swoboda
Paweł Swoboda

Reputation: 31

There is also negative lookbehind function (PowerGREP or Perl flavor). It works perfectly for my purposes. Regex:

(?<!\s+)^(.+)$

where

  • (?<!\s+) is negative lookbehind - regex matches only strings that are not preceded by a whitespace(s) (\s also stands for a line break)
  • ^ is start of a string
  • (.+) is a string
  • $ is end of string

Upvotes: 3

Ivaprag
Ivaprag

Reputation: 631

In case you need the very first line no matter what, here you go:

 \A.*

It will select the first line, no matter what.

Upvotes: 34

polemon
polemon

Reputation: 4772

that's sounds more like a job for the filehandle buffer.

You should be able to match the first line with:

/^(.*)$/m

(as always, this is PCRE syntax)

the /m modifier makes ^ and $ match embedded newlines. Since there's no /g modifier, it will just process the first occurrence, which is the first line, and then stop.

If you're using a shell, use:

head -n1 file

or as a filter:

commandmakingoutput | head -n1

Please clarify your question, in case this is not wat you're looking for.

Upvotes: 44

Topera
Topera

Reputation: 12389

Yes, you can.

Example in javascript:

"This is the first line.\n This is the second line.".match(/^.*$/m)[0];

Returns 

"This is the first line."

EDIT

Explain regex:

match(/^.*$/m)[0]

  • ^: begin of line
  • .*: any char (.), 0 or more times (*)
  • $: end of line.
  • m: multiline mode (. acts like a \n too)
  • [0]: get first position of array of results

Upvotes: 21

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