Delete empty lines using sed

Question

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?

Answer 1

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.)

Answer 2

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 fields, 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.

Answer 3

sed

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

grep

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

awk

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

Answer 4

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.

Answer 5

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

Answer 6

Another option without sed, awk, perl, etc

strings $file > $output

strings - print the strings of printable characters in files.

Answer 7

With help from the accepted answer here and the accepted answer above, I have used:

$ sed 's/^ *//; s/ *$//; /^$/d; /^\s*$/d' file.txt > output.txt

`s/^ *//`  => left trim
`s/ *$//`  => right trim
`/^$/d`    => remove empty line
`/^\s*$/d` => delete lines which may contain white space

This covers all the bases and works perfectly for my needs. Kudos to the original posters @Kent and @kev

Answer 8

The command you are trying is correct, just use -E flag with it.

sed -E '/^$/d'

-E flag makes sed catch extended regular expressions. More info here

Answer 9

You can say:

sed -n '/ / p' filename    #there is a space between '//'

Answer 10

You are most likely seeing the unexpected behavior because your text file was created on Windows, so the end of line sequence is \r\n. You can use dos2unix to convert it to a UNIX style text file before running sed or use

sed -r "/^\r?$/d"

to remove blank lines whether or not the carriage return is there.

Answer 11

This works in awk as well.

awk '!/^$/' file
xxxxxx
yyyyyy
zzzzzz

Answer 12

You can do something like that using "grep", too:

egrep -v "^$" file.txt

Answer 13

My bash-specific answer is to recommend using perl substitution operator with the global pattern g flag for this, as follows:

$ perl -pe s'/^\n|^[\ ]*\n//g' $file
xxxxxx
yyyyyy
zzzzzz

This answer illustrates accounting for whether or not the empty lines have spaces in them ([\ ]*), as well as using | to separate multiple search terms/fields. Tested on macOS High Sierra and CentOS 6/7.

FYI, the OP's original code sed '/^$/d' $file works just fine in bash Terminal on macOS High Sierra and CentOS 6/7 Linux at a high-performance supercomputing cluster.

Answer 14

If you want to use modern Rust tools, you can consider:

• ripgrep:
  • cat datafile | rg '.' line with spaces is considered non empty
  • cat datafile | rg '\S' line with spaces is considered empty
  • rg '\S' datafile line with spaces is considered empty (-N can be added to remove line numbers for on screen display)
• sd
  • cat datafile | sd '^\n' '' line with spaces is considered non empty
  • cat datafile | sd '^\s*\n' '' line with spaces is considered empty
  • sd '^\s*\n' '' datafile inplace edit

Answer 15

Using vim editor to remove empty lines

:%s/^$\n//g

Answer 16

For me with FreeBSD 10.1 with sed worked only this solution:

sed -e '/^[     ]*$/d' "testfile"

inside [] there are space and tab symbols.

test file contains:

fffffff next 1 tabline ffffffffffff

ffffffff next 1 Space line ffffffffffff

ffffffff empty 1 lines ffffffffffff

============ EOF =============

Answer 17

NF is the command of awk you can use to delete empty lines in a file awk NF filename and by using sed sed -r "/^\r?$/d"