Thanks for all the replies, I will try to answer them all

Yes I did mean "$_ contains the value 'PID: , VID: 255, SN: AGM163923J5". So this wasn't a section of the perl code. I am reading a file and it is at this line that strangeness happens.

Yes I am using Strict and Warnings

I have put the output direct from the Cisco CLI through a Hex translator and there doesn't seem to be any hidden/null characters

PID: , VID:

0x500x490x440x3a0x200x2c0x200x560x490x440x3a

but the output from the file perl is holding the string in does have extra characters.

0x500x490x440x3a 0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x7f0x2c 0x560x490x440x3a

Thanks for all your help