How to remove blank lines from a file using shell script or unix command?

Question

I am using below script to validate IPV6 address but this script also pass invalid IP such as empty string, name etc.

if [[ "$IPv6ADDR"=~"^:?([a-fA-F0-9]{1,4}(:|.)?){0,8}(:|::)?([a-fA-F0-9]{1,4}(:|.)?){0,8}$" ]]; then
  echo "valid ipv6 addr"
  break;
else
  echo "Invalid IP Address"
  break;
fi

Can someone identify what's wrong in the regex, Please?

Answer 1

Unix Command:
$ grep -v '^$' File_Name > Temp_File | mv Temp_File File_Name

1) By grep option you can search the pattern of blank lines, i.e. '^$'
2) by -v option is takes a negation of the patter which you are searching by grep command.

$ grep -v '^$' File_Name > Temp_File

So, by above command you are identifying Non-Duplicate lines from your file and writing it to a Temp_File.

After that by piping command you are moving the data from your Temp_File to your Original File and hence your output would be achieved.

If you like my answer please vote on me....thanks...

Hope it helps you....
Arif

Comments

Wonderful my +1 :)

Answer 2

You can use any one of the following utility to delete all empty lines from text file:

[a] sed command

[b] awk command

[c] perl command
Syntax

The syntax is:

command input.txt > output.txt

command [option] input.txt > output.txt



sed '...' input.txt > output.txt

## Gnu/sed
sed -i '...' input.txt

awk '...' input.txt > output.txt

sed command examples

Type the following sed command to delete all empty files:

sed '/^$/d' input.txt > output.txt
cat output.txt

OR

sed -i '/^$/d' input.txt
cat input.txt

awk command examples

Type the following awk command to delete all empty files:

awk 'NF > 0' input.txt > output.txt
cat output.txt

perl command examples

Type the following perl one liner to delete all empty files and save orignal file as input.txt.backup:

perl -i.backup -n -e "print if /\S/" input.txt

Verify updated files, type:

cat input.txt
cat input.txt.backup