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How can I shorten the data that I retrieve once I enter a command? For example if I input:

ifconfig -a getifaddr

I only want the IP address, nothing else. Surely there is something else that I can add to my command to simply pinpoint answers in the mass flow of text that is retrieved?

FYI the example command was simply an example

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  • 1
    I usually use a combination of grep and cut to isolate a known piece of output. You can pipe (|) the output to these commands. See man grep and man cut. – amc Jul 8 '16 at 6:28
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    ^ What he said, but there are many, many more tools to specifically parse out information: awk, head, tail, cut, you name it. Then you can also use perl, python, i.c.w regex or not ... There is not a one fits all answer to it. – Jacob Vlijm Jul 8 '16 at 6:42
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A clever use of pipes is usually the answer. For example you can use the raw ifconfig output:

$ ifconfig eth0
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.0.4  netmask 255.255.255.0  broadcast 192.168.0.255
        inet6 fe80::ca60:ff:fe06:ac5b  prefixlen 64  scopeid 0x20<link>
        ether c8:60:00:06:ac:5b  txqueuelen 1000  (Ethernet)
        RX packets 622902  bytes 792538068 (755.8 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 392538  bytes 37764707 (36.0 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

And then carve away this output until you see the information you are after:

$ ifconfig eth0 | grep -w inet | cut -d ' ' -f 10
192.168.0.4

My own choice of weapons:

  1. Use grep with the -w option to search for only whole word matches. This way we do not catch inet6 as well.
  2. Use cut with a delimiter (-d) of a space and then select the appropriate field (-f) number to get the information we are after.

There are many, many tools to do this and doubtless a better way to accomplish this particular job. But this example shows the use of pipes and several of the tools that you can use.

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4

To add to andrew.46s answer here is how you can do it with awk and sed. Needs as well the clever use of pipes.

ifconfig -a | awk '/inet/{print $2;}' | sed 's/addr://'

makes:

127.0.0.1
192.168.0.12

from:

enp2s0    Link encap:Ethernet  HWaddr 18:a9:05:e3:f6:ca  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
          Interrupt:16 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:13845 errors:0 dropped:0 overruns:0 frame:0
          TX packets:13845 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1 
          RX bytes:1594329 (1.5 MB)  TX bytes:1594329 (1.5 MB)

wlp6s0    Link encap:Ethernet  HWaddr c4:17:fe:20:10:ed  
          inet addr:192.168.0.12  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::c617:feff:fe20:10ed/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:104772 errors:0 dropped:0 overruns:0 frame:3603935
          TX packets:78681 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:90707841 (90.7 MB)  TX bytes:14272953 (14.2 MB)
          Interrupt:17
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