#!/usr/bin/perl
use 5.016;
use warnings;

# 1059623
# select lines which do not have : at the first word. 

my @arry=(
        'bond0.2 Link encap:Ethernet',
        'bond4.3:6 Link encap:Ethernet',
        'bond3 Link encap:Ethernet',
        'bond5:0 Link encap:Ethernet',
        'bond1.5:2 Link encap:Ethernet',
        'bond2.6 Link encap:Ethernet'
);

my $elem;
for $elem(@arry) {
       if($elem =~ /(bond[^:]+?)\s+Link.*$/) {  # note negated char class, minimally
                my $match = $1;                 # You may find it 'good practice' to extract 
                                                # any value in $1 to another var ASAP
                say $match . " The colon, if any, is AFTER the first word \n\tin | \"$elem\" |";
        } else {
                say "Matching colon in first word (ie, before a space)\n\t in | \"$elem\" |";
        }
}

=head

C:\>1059623.pl
bond0.2 The colon, if any, is AFTER the first word
        in | "bond0.2 Link encap:Ethernet" |
Fails OP's criterion; matching colon in first word (ie, before a space)
         in | "bond4.3:6 Link encap:Ethernet" |
bond3 The colon, if any, is AFTER the first word
        in | "bond3 Link encap:Ethernet" |
Fails OP's criterion; matching colon in first word (ie, before a space)
         in | "bond5:0 Link encap:Ethernet" |
Fails OP's criterion; matching colon in first word (ie, before a space)
         in | "bond1.5:2 Link encap:Ethernet" |
bond2.6 The colon, if any, is AFTER the first word
        in | "bond2.6 Link encap:Ethernet" |

C:\>

=cut