CODEWITHSUNDEEP
regex
David says Reinstate Monica
David says Reinstate Monica

Reputation: 20139

Multiline regex match for only the start of a file

How can I match a pattern only at the start of a file? In my particular usecase I have a script with a bunch of comments in the header and potential comments in the body, and I only want to remove the header comments.

# blah blah
# More blah
# Hello World
Actual stuff
# commented out stuff
More stuff

Should map to 

Actual stuff
# commented out stuff
More stuff

The regex I've tried is /^#.*$//mg, but this will match the comments in the body as well. How can I restrict it to only the comments in the header? Additionally, I don't want to leave blank lines at the head of the file.

Upvotes: 0

Views: 50

Answers (2)

Casimir et Hippolyte
Casimir et Hippolyte

Reputation: 89639

With sed:

sed -n '1{:a;/^#/n;/^#/ba};p' file.txt

details:

1        # if the line number is 1
{        # do
  :a;    # define the label a
  /^#/n; # when the line begins with # load the next line in pattern space
  /^#/ba # if the "new" line begins with # go to label a
};
p        # print the line

With the n parameter, the lines are no more automatically printed.

Upvotes: 1

anubhava
anubhava

Reputation: 786091

You can use this awk:

awk '/^[^#]/{body=1} body' file
Actual stuff
# commented out stuff
More stuff

Upvotes: 1

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