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With a bash script, can I read the mac address of my eth0 and print it to a file?

Gilles 'SO- stop being evil'
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michelemarcon
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4 Answers4

15

ifconfig will output information about your interfaces, including the MAC address:

$ ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:11:22:33:44:55  
          inet addr:10.0.0.1  Bcast:10.0.0.255  Mask:255.0.0.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:289748093 errors:0 dropped:0 overruns:0 frame:0
          TX packets:232688719 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:3264330708 (3.0 GiB)  TX bytes:4137701627 (3.8 GiB)
          Interrupt:17

The HWaddr is what you want, so you can use awk to filter it:

$ ifconfig eth0 | awk '/HWaddr/ {print $NF}'
00:11:22:33:44:55

Redirect that into a file:

$ ifconfig eth0 | awk '/HWaddr/ {print $NF}' > filename
Michael Mrozek
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    You can also use th `ip` command: `/sbin/ip link show eth0`. – Keith Apr 18 '11 at 20:39
  • @Keith I don't have that command, I'm not sure which package it's in; I think `ifconfig` is fairly standard – Michael Mrozek Apr 18 '11 at 20:49
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    @Michael On Linux anyway, it is the [preferred tool](http://lartc.org/lartc.html#LARTC.IPROUTE2.WHY). In fact you must use to configure some advanced features. But ifconfig lives on... – Keith Apr 18 '11 at 20:55
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    The international approach is `LC_ALL=C ifconfig eth0 | awk '/HWaddr/ {print $NF}'`, because the output might be localized, not matching 'HWaddr'. LC_ALL=C uses the international standard. – user unknown Apr 19 '11 at 00:21
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    @user Ah, cool. As far as I know it'll always be the first line, so you could just get away with `awk '{print $NF; exit}'` too – Michael Mrozek Apr 19 '11 at 00:31
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    Yes, if you're the AWK-type. I'm the sed-type, but would here prefer an `| head -n 1` then. – user unknown Apr 19 '11 at 03:53
  • I know this is Unix & Linux community but this also works on QNX 6.5. – IsaacS Dec 31 '14 at 05:23
10

Here's a modern Linux method:

ip -o link show dev eth0 | grep -Po 'ether \K[^ ]*'

It's modern in that ifconfig has long been deprecated in favour of ip from the iproute2 package, and that grep has the -P option for perl regular expressions for the zero-width positive look-behind assertion.

grep -o is nice for text extraction. sed is traditionally used for that but I find the perl-style zero-width assertions clearer than a sed substitution command.

You don't actually need the -o (oneline) option to ip, but I prefer to use it when extracting network information since I find it cleaner having one record per line. If you're doing more complicated matches or extractions (usually with awk), -o is essential for a clean script, so for the sake of consistency and a common pattern, I always use it.

Edit: Updating 10 years later: ip now has the -j flag for JSON output, and when combined with jq, it provides a more robust and readable command pipeline:

ip -j link show dev eth0 | jq -r '.[0].address'

The -r flag to jq makes it output a raw string instead of a quoted (JSON) string.

camh
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5
#! /bin/sh

/sbin/ifconfig eth0 | perl -ne 'print "$1\n" if /HWaddr\s+(\S+)/' >file

There are other tools that could cut the MAC address out of ifconfig's output, of course. I just like Perl.

cjm
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0

Using ip -br link show eth0 will print something like this:

$ ip -br link show eth0 
eth0             UP             85:e2:62:9c:b2:02 <BROADCAST,MULTICAST,UP,LOWER_UP>

You only need the 3rd column, so:

$ ip -br link show eth0 | awk '{ print $3 }'
85:e2:62:9c:b2:02
$ ip -br link show eth0 | awk '{ print $3 }' > file
annahri
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