Re: newlines in regular expressions

The keys as it were are to note that \n\n is a blank line or if you read a file line by line then a blank line will match m/^\s*$/

perl -pi.bak -e 's/\n{2,}/\n/' file.txt

perl -pi -e 's/^\s*\z//' file.txt

perl -ne 'print unless m/^\s*$/' file.txt > noblanks.txt
[download]

Updated as per sgifford's comments.

cheers

tachyon

Comment on Re: newlines in regular expressions Download Code

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Re^2: newlines in regular expressions by sgifford (Prior) on Dec 07, 2004 at 06:57 UTC
A few nits: The first answer requires that Perl read in slurp mode, and needs a `g` modifier to replace all occurences: `perl -p -e 'BEGIN { undef $/ } s/\n{2,}/\n/g'` [download] Also, the two examples behave differently in the face of lines that contain only blank characters, like space and tab. The second will delete them, while the first will leave them intact. You can make the second leave them intact by using `m/^$/`; to make the first delete whitespace-only lines I think `s/\n\s*\n/\n/g` will work, but I haven't thought it through yet.	[reply] [d/l] [select]
Re^3: newlines in regular expressions by eyepopslikeamosquito (Archbishop) on Dec 07, 2004 at 07:22 UTC
`perl -p -e 'BEGIN { undef $/ } s/\n{2,}/\n/g'` [download] Which can be shortened to: `perl -p0777e 's/\n{2,}/\n/g'` [download] See `perldoc perlrun` for details of perl's `-0` option.	[reply] [d/l] [select]
Re^3: newlines in regular expressions by tachyon (Chancellor) on Dec 07, 2004 at 12:09 UTC
`perl -pi -e 's/^\s*\z//' file.txt` deals with blank lines with other whitespace.	[reply] [d/l]
Re^3: newlines in regular expressions by tachyon (Chancellor) on Dec 07, 2004 at 11:59 UTC
It is as you say.	[reply]