regular expression: match multiple newlines

wegelin has asked for the wisdom of the Perl Monks concerning the following question:

I work at the unix command line (bash shell) on a Mac 10.6.8. In a text file, I want to replace all multiple newlines, even if the newlines have other whitespace between them, with EEEEE. All single newlines I want to leave alone. Thus the following file, called textfile:

dogs rats
cats

fish

must be transformed into

dogs rats
catsEEEEEfish

But as you see from the example below, the following regular expression, issued at the command line, doesn't do it.

s/\n\s*\n/EEEEE/g
[download]

Here is the example:

> cat textfile
dogs rats
cats

fish
> perl -p -e 's/\n\s*\n/EEEEE/g' textfile
dogs rats
cats

fish

Is there a simple or elegant solution?

Comment on regular expression: match multiple newlines Download Code

Replies are listed 'Best First'.
Re: regular expression: match multiple newlines by Cristoforo (Curate) on Nov 03, 2013 at 19:42 UTC
Your code is reading 1 line at a time. You need to 'slurp' the file and apply the regular expression. `perl -0 -p -e 's/\n\s*\n/EEEEE/g' textfile`	[reply] [d/l]
Re^2: regular expression: match multiple newlines by Kenosis (Priest) on Nov 03, 2013 at 19:55 UTC
~~Good point! However, `\n\s*\n` would replace `\n\x20\n` --a space surrounded by two newlines--which is not two consecutive newlines, thus the prior `\n{2,}` suggestion.~~ Edit: My apologies. Didn't notice the the OP's mentioning the possibility of other whitespace between the newlines.	[reply] [d/l] [select]
Re^3: regular expression: match multiple newlines by Cristoforo (Curate) on Nov 03, 2013 at 20:13 UTC
He stated that there might be spaces between the newlines :-)	[reply]
Re^4: regular expression: match multiple newlines by Kenosis (Priest) on Nov 03, 2013 at 20:47 UTC
Re: regular expression: match multiple newlines by Lennotoecom (Pilgrim) on Nov 04, 2013 at 01:22 UTC
/(?<=\S)\s*$/ ? ({print "$a$`"},$a="\n") : ($a='EEEEE') while <DATA>; __DATA__ dogs rats cats fish text cats2 fish2 text3 [download] output: `dogs rats catsEEEEEfish text cats2EEEEEfish2 text3` [download]	[reply] [d/l] [select]
Re: regular expression: match multiple newlines by Kenosis (Priest) on Nov 03, 2013 at 19:38 UTC
Try: `s/\n{2,}/EEEEE/g` [download] Output on your dataset: `dogs rats catsEEEEEfish` [download] The `\n{2,}` notation matches 2+ newlines. Edit: My apologies. Didn't notice the the OP's mentioning the possibility of other whitespace between the newlines.	[reply] [d/l] [select]

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