Delete empty lines using sed

I am trying to delete empty lines using sed:

sed '/^$/d'

but I have no luck with it.

For example, I have these lines:

xxxxxx


yyyyyy


zzzzzz

and I want it to be like:

xxxxxx
yyyyyy
zzzzzz

What should be the code for this?

You may have spaces or tabs in your "empty" line. Use POSIX classes with sed to remove all lines containing only whitespace:

sed '/^[[:space:]]*$/d'

A shorter version that uses ERE, for example with gnu sed:

sed -r '/^\s*$/d'

(Note that sed does NOT support PCRE.)

I am missing the awk solution:

awk 'NF' file

Which would return:

xxxxxx
yyyyyy
zzzzzz

How does this work? Since NF stands for "number of fields", those lines being empty have 0 fiedls, so that awk evaluates 0 to False and no line is printed; however, if there is at least one field, the evaluation is True and makes awk perform its default action: print the current line.

sed '/^$/d' should be fine, are you expecting to modify the file in place? If so you should use the -i flag.

Maybe those lines are not empty, so if that's the case, look at this question Remove empty lines from txtfiles, remove spaces from start and end of line I believe that's what you're trying to achieve.

sed

• '/^[[:space:]]*$/d'
• '/^\s*$/d'
• '/^$/d'
• -n '/^\s*$/!p'

grep

• .
• -v '^$'
• -v '^\s*$'
• -v '^[[:space:]]*$'

awk

• /./
• 'NF'
• 'length'
• '/^[ \t]*$/ {next;} {print}'
• '!/^[ \t]*$/'

I believe this is the easiest and fastest one:

cat file.txt | grep .

If you need to ignore all white-space lines as well then try this:

cat file.txt | grep '\S'

Example:

s="\
\
a\
 b\
\
Below is TAB:\
    \
Below is space:\
 \
c\
\
"; echo "$s" | grep . | wc -l; echo "$s" | grep '\S' | wc -l

outputs

7
5