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whatismylocalip alias (actually more like whataremylocalips) and some sed links

Posted by jpluimers on 2017/01/10

Getting the local IP (actually IPs, but most hosts only have a single IP):

# OS X:
alias whatismylocalip='ifconfig | sed -En '\''s/;s/.*inet (addr:)?(([0-9]*\.){3}[0-9]*).*/\2/p'\'''
# Linux:
alias whatismylocalip='ip a | sed -En '\''s/;s/.*inet (addr:)?(([0-9]*\.){3}[0-9]*).*/\2/p'\'''

I got them via bash – How to I get the primary IP address of the local machine on Linux and OS X? – Stack Overflow

Mac OS X and BSD have ifconfig, but most Linux distributions don’t use ifconfig any more in favour of iproute2, so you use ip a (which is shorthand for ip address show) there.

Their output is similar enough for the sed to work, though. Which surprised be because I didn’t know about the -E option (it lacks in the manual Linux page but it is in the Mac OS X one) which enables POSIX extended regular expressions. In Linux this is documented as -r, but -E also works.

I learned this through the Sed – An Introduction and Tutorial which compares the various versions of sed which also explains about the -n doing no printing.


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