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regexperlmultiline

Match multiline and print it in perl regex

I want to match a multiline regex and print only the lines that match:

$ cat test.txt
line1
line2
line3
$ perl -ne 'print if /line2.line3/s' test.txt
$

This regex actually matches line2\nline3 but it is not printed. regex101 verifies that it is matched.

Using command switch 0777 prints the lines that match but then it prints non-matched lines too:

$ perl -0777 -ne 'print if /line2.line3/s' test.txt
line1
line2
line3

Using 0777 in a substitution regex works as expected:

$ perl -0777 -pe 's/line2.line3/replaced/s' test.txt
line1
replaced

I would like to learn if it is possible to print only lines that match a multiline regex?

Solution

  • print without an argument prints $_. If you use -0777, the whole file is read into $_, so if there is a match, you print the whole file. If you only want to show the matching parts, you can use

     perl -0777 -ne 'print "$1\n" while /(line2.line3)/sg' test.txt