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egrep -wo '([0-9]{1,3}\.){3}[0-9]{1,3}' file.txt
selects on word boundaries and is slightly less verbose
cool didn't know about the -o option ....
perl version:
perl -ne's/(\d{1,3}\.){3}\d{1,3}/print"$&\n"/ge' file.txt
and, perl version (word boundary):
perl -ne's/\b(\d{1,3}\.){3}\d{1,3}\b/print"$&\n"/ge' file.txt
This is all *plain wrong*, you extract 4 numbers (Each up to three digits) seperated by dots with these regexes. These numbers don't have to be valid IPs.
See:
echo "999.999.999.999" > file.txtecho "10.1.12.23" >> file.txtperl -ne's/(\d{1,3}\.){3}\d{1,3}/print"$&\n"/ge' file.txt999.999.999.999
10.1.12.23
egrep -o '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' file.txt999.999.999.999
10.1.12.23
Better use sth. like that (Not mine, found with google):
egrep '\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b' file.txt10.1.12.23