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Previous: 25.9 Adding and Deleting White Space Chapter 25
Showing What's in a File
Next: 25.11 crush: A cat that Skips all Blank Lines
 

25.10 Squash Extra Blank Lines

Reading output with lots of empty lines can be a waste of screen space. For instance, some System V versions of man ( 50.1 ) show all the blank lines between manual pages. To stop that, read your file or pipe it through cat -s . (Many versions of more ( 25.3 ) have a similar -s option.) The -s option replaces multiple blank lines with a single blank line. (If your cat doesn't have -s , see the sed alternative at the end.)

cat -s might not always seem to work. The problem is usually that the "empty" lines have SPACE, TAB, or CTRL-m characters on them. The fix is to let sed "erase" lines with those invisible characters on them:

% 

sed 's/^[
[SPACE]

[TAB]

[CTRL-v]

[CTRL-m]
]*$//' 



file



 | cat -s

In vi ( 31.6 ) and many terminal drivers ( 42.1 ) , the CTRL-v character quotes the CTRL-m (RETURN) so that character doesn't end the current line.

If you don't have cat -s , then sed can do both jobs:

% 

sed -e 's/^[
[SPACE]

[TAB]

[CTRL-v]

[CTRL-m]
]*$//' -e '/./,/^$/!d' 



file

- JP


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