How to remove blank lines in .txt files

Question

I want to change a text file's format, removing all blank lines. How can I do that?

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(2) 5. The function of the condenser is to:

a) vapourise the liquid refrigerant

b) change high pressure refrigerant vapour to liquid

c) pressurise low pressure refrigerant vapour

d) vent off vapourised refrigerant

e) lower the liquid refrigerant pressure

(2) 6. One tonne of refrigeration is:

a) 13958 kJ per day

b) 100 kJ per minute

c) 233 kJ per minute

d) 13958 J per hour

e) 335 J per second

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(2) 5. The function of the condenser is to:
a) vapourise the liquid refrigerant
b) change high pressure refrigerant vapour to liquid
c) pressurise low pressure refrigerant vapour
d) vent off vapourised refrigerant
e) lower the liquid refrigerant pressure

(2) 6. One tonne of refrigeration is:
a) 13958 kJ per day
b) 100 kJ per minute
c) 233 kJ per minute
d) 13958 J per hour
e) 335 J per second

Answer 1

You can use GNU sed:

sed -i -e "/^$/d" su.txt

Will delete blank lines.

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If you're on a BSD variant or OS X, use this instead:

sed -i '' -e "/^$/d" su.txt

Here, -i takes an extension as an argument – using the GNU sed syntax would result in a file su.txt-e being created.

Answer 2

This can be achieved by using grep:

grep . file

Or try the ex-way (cross-platform compatible):

ex -s +'v/\S/d' -cwq test.txt

For multiple files (edit in-place):

ex -s +'bufdo!v/\S/d' -cxa *.txt

^{Note: The :bufdo command is not POSIX.}

Without modifying the file (just print on the standard output):

cat test.txt | ex -s +'v/\S/d' +%p +q! /dev/stdin