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(冷日) 發表時間：2016/8/25 12:10

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註冊日: 2008/2/19
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[轉貼]Delete empty lines using SED

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 this lines:

xxxxxx


yyyyyy


zzzzzz

and i want it to be like:

xxxxxx
yyyyyy
zzzzzz

what should be the code for this?

you may have space/tabs in your "empty" line try this, see if it helps:

sed '/^\s*$/d'

Where \s matches any whitespace character.

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.

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

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.

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

You can say:

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

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

egrep -v "^$" file.txt

原文出處：linux - Delete empty lines using SED - Stack Overflow

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