Can you show a sample line from the log? If it is just anything followed by a space and the ip, this should be enough: 
perl -i~ -pe ' s/(.*) ([0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3})
+$/$2 $1/;' 2001-01-02.log

[download]
I used the following data for testing:
234.234.234.234.asd.f2.35.346t.sdfg.aws.5332.6t.sdf.as4.23.4234 12.12.
+153.43

[download]
BTW, this is a shorter version of the regex: s/(.*) ((?:[0-9]{1,3}\.){3}[0-9]{1,3})$/$2 $1/
لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re: reformat log files by choroba
in thread reformat log files by Anonymous Monk

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