Unix perl match string and delete line

Question

Im using perl to remove a string from a file, it is removing the string from file, But the actual line is not getting deleted, Due to which the next insert to the files are getting written over next line.

Perl command used:

host=ABC1234
perl -lpi -e "s/$host//g" /tmp/exclude_list

output:

ABC1234 

Answer 1

With

cp /tmp/exclude_list /tmp/exclude_list.tmp
grep -Fx -v -e "$host" /tmp/exclude_list.tmp >/tmp/exclude_list
rm /tmp/exclude_list.tmp

you would remove each line that exactly matches the string in $host. Change -Fx to just -F to remove any line that contains the string. Don't use -F if you want to use $host as a regular expression.

Or with Perl:

perl -i -sn -e 'print unless /$host/' -- -host="$host" /tmp/exclude_list

The options used with perl here is -i for in-place editing, -s to allow Perl to instantiate the $host Perl variable from the command line, and -n to only print explicitly from within the implicit loop that Perl provides around the code. The -e takes the actual code as the argument.

The Perl code would remove all lines that does not match the regular expression $host.

To use $host as a string:

perl -i -sn -e 'print unless index($_, $host) >= 0' -- -host="$host" /tmp/exclude_list