Question

Details:

I am reading a file in an incoming stream using tail -f

I am able to find and replace characters/strings in the stream using sed, something like:

tail -f a.log | sed 's/'`echo -e "\xnn"`'/'`echo "$(tput setaf 1)|sep|$(tput sgr0)"`'/g'

What the above achieves is give me a clear visual marker for the separator string (which is non-printable hex character nn in this case, nn might be 05 as an example, replacing it with a red (in this case) colored (via tput) string |sep|.

So I get something like

field **|sep|** field **|sep|** field **|sep|**

What I want is

field **|sep#1|** field **|sep#2|** field **|sep#3|**

So, the requirement is to have the nth match marked as such in the substitution string (|sepn| where n is the no. of match encountered)

Answer 1

Use Perl’s ability to evaluate replacement on the fly to keep track of number of replacements made:

my $str='field **|sep|** field **|sep|** field **|sep|**';
my $str2='saodifuasd|sep|psaoidugfsdoif|sep|sdoiufd';
my $cnt;
$cnt=0; $str=~s/\|sep\|/"|sep#".$cnt++."|"/ge;
$cnt=0; $str2=~s/\|sep\|/"|sep#".$cnt++."|"/ge;
print "$str\n";
print "$str2\n";

Result:

field **|sep#0|** field **|sep#1|** field **|sep#2|**
saodifuasd|sep#0|psaoidugfsdoif|sep#1|sdoiufd

As you see, you will have to manually reset separator counter on every line.