How can i modify this sed command to remove the trailing colon on the output

Question

I need to show the ethernet interfaces on a Centos 7 server. On centos 6.5, I was using this command (from another post)and it works fine on 6.5.

ifconfig -a | sed  -n 's/^\([^ ]\+\).*/\1/p' | grep -Fvx -e lo 

on Centos 7 the interface output now has a trailing ":"

so my output look like this

ifconfig -a | sed  -n 's/^\([^ ]\+\).*/\1/p' | grep -Fvx -e lo
ens32:
lo:

to remove the "lo:" I modified to this. which results in ens32:

ifconfig -a | sed  -n 's/^\([^ ]\+\).*/\1/p' | grep -Fvx -e lo:
ens32:

How can I remove the trailing ":" ? can this sed be modified? or other ideas

Answer 1

It is unfortunate that you don't provide the raw output of the ifconfig command. But I would go to something like that :

$ ifconfig -a | perl -anle 'print $F[0] if /(^\w)/'
$  enp2s0f0
   lo
   tun0
   wlp3s0b1

Raw output is the following:

enp2s0f0  Link encap:Ethernet  HWaddr 3c:07:54:5f:5e:35  
          inet addr:192.168.1.114  Bcast:192.168.1.255 
[...] 

perl -anle, where is 'a' split the line in column and fill the variable $F 'n' is to process the output line by line, 'l' is to put a new line between every print and 'e' is to execute the perl command in command line. Then follow the regex where I simply say that I want to match the line '//' that contains one char '\w' at the beginning of the line '^'.

Answer 2

This will work on old systems without the colon and on new systems with the colon:

$ /sbin/ifconfig -a | awk -F'[ :]+' '$1 && $1!="lo" {print $1}'
eth0

Alternatively, using sed, this will also work on both new and old systems:

$ /sbin/ifconfig -a | sed -n 's/[ :].*//; /^lo$/t; /./p'
eth0

When awk or sed are used, it is rare to need an additional process to run grep.

How the awk command works

• -F'[ :]+'

  This tells awk to treat any consecutive blanks or colons as a field separator.

• $1 && $1!="lo" {print $1}

  If there is a first field and if that field is not lo, then print it.

How the sed command works

• -n

  This tells sed not print anything unless explicitly asked to.

• s/[ :].*//

  This tells sed to remove everything from the first space or colon to the end of the line.

• /^lo$/t

  If the line matches lo, then skip the rest of the commands and start over on the next line.

• /./p

  If the line contains any characters at all, print the line.