使用 sed 删除空行

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 '/^$/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 4

sed

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

grep

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

awk

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

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

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 7

Another option without sed , awk , perl , etc

strings $file > $output

strings - print the strings of printable characters in files.

Answer 8

你可以说：

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

Answer 9

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 10

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 11

你也可以使用“grep”来做类似的事情：

egrep -v "^$" file.txt

Answer 12

This works in awk as well.

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

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' 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' '' cat datafile | sd '^\n' '' line with spaces is considered non empty
  • cat datafile | sd '^\s*\n' '' cat datafile | sd '^\s*\n' '' line with spaces is considered empty
  • sd '^\s*\n' '' datafile inplace edit

Answer 15

NF 是 awk 的命令，可用于删除文件awk NF filename中的空行，并使用 sed sed -r "/^\r?$/d"

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

使用 vim 编辑器删除空行

:%s/^$\n//g