Shell Programming and Scripting

sed -r 's/(\.[0-9][0-9])([^§])/\1§\2/2' file

sed -r          # switching on ERE (extended regex) behaviour
'               # single quote to open the first parameter
s               # substitute command
/               # default char to open a regex
(               # opening the first parenthesized subexpression for back reference
\.[0-9][0-9]    # regex: escaped dot, double digit
)               # closing first par. subexp.
([^§])          # second par. subexp.: any char except §
/               # default char to switch from matching pattern to replacement string
\1              # use first back reference
§               # insert literal §
\2              # use second b.r.
/               # close replacement string
2               # option flag: apply to second occurrence only
'               # close first parameter
 file           # file to read / modify

$ 
$ cat -n replace_occurrences.pl 
     1    #!/usr/bin/perl
     2    # Usage: perl replace_occurrences.pl data.txt 2      # replace 2nd occurrence only
     3    #        perl replace_occurrences.pl data.txt 2,4,5  # replace 2nd, 4th, 5th occurrences
     4    #        perl replace_occurrences.pl data.txt 2-6    # replace 2nd through 6th occurrences
     5    #        perl replace_occurrences.pl data.txt        # replace all occurrences
     6    #        perl replace_occurrences.pl data.txt 3-     # replace the 3rd and all occurrences after it
     7    use strict;
     8    my $infile = $ARGV[0];
     9    my $rep_range = $ARGV[1];
    10    my %rep;
    11    my $till_the_end = 0;
    12    my $start_index;
    13    
    14    # Subroutine section
    15    sub set_rep_indexes {
    16        if ($rep_range =~ /^\d+$/) {
    17            $rep{$rep_range}++;
    18        } elsif ($rep_range =~ /,/) {
    19            %rep = map {$_ => 1} split(',', $rep_range);
    20        } elsif ($rep_range =~ /(\d+)-(\d+)/) {
    21            for(my $i=$1; $i<=$2; $i++) { $rep{$i}++ }
    22        } elsif ($rep_range eq "" or $rep_range =~ /(\d+)-/) {
    23            $start_index = $rep_range eq "" ? 1 : $1;
    24            $till_the_end = 1;
    25        }
    26    }
    27    
    28    sub replace_occurrences {
    29        my $x = shift;
    30        my ($str, $pre, $token, $post) = ("", "", "", "");
    31        my $count = 1;
    32        do {
    33            ($pre, $token, $post) = $x =~ /(.*?)(\.\d\d)([^§])/;
    34            if ($pre ne "") {
    35                if (($till_the_end and $count >= $start_index) or defined $rep{$count}) {
    36                    $str .= "${pre}${token}§${post}"
    37                } else {
    38                    $str .= "${pre}${token}${post}"
    39                }
    40                $x =~ s/$pre$token$post//;
    41                $count++;
    42            }
    43        } until ($pre eq "");
    44        $str .= $x;
    45        return $str;
    46    }
    47    
    48    # Main section
    49    set_rep_indexes;
    50    open(FH, '<', $infile) or die "Can't open $infile: $!";
    51    while (<FH>) {
    52        chomp(my $line = $_);
    53        print replace_occurrences($line),"\n";
    54    }
    55    close(FH) or die "Can't close $infile: $!";
    56    
$ 
$ # Original and unchanged pattern is in red, modified pattern is in purple.
$ cat data.txt
1007937820§L§2016-12-19§000000002§2018-02-01§2050-12-01§00395§M§146713.57§00005.05000§762.59§00395§M§301223.0528§1165§2017-03-31 20:34:25
0.556abc§def§0005.0500§ghi§jkl§123.45§678§mn§opq§5678.90123§rs§tuvw§0.1234§xyz§6.55
$ 
$ perl replace_occurrences.pl data.txt 2
1007937820§L§2016-12-19§000000002§2018-02-01§2050-12-01§00395§M§146713.57§00005.05000§762.59§00395§M§301223.05§28§1165§2017-03-31 20:34:25
0.556abc§def§0005.05§00§ghi§jkl§123.45§678§mn§opq§5678.90123§rs§tuvw§0.1234§xyz§6.55
$ 
$ perl replace_occurrences.pl data.txt 1,2,4
1007937820§L§2016-12-19§000000002§2018-02-01§2050-12-01§00395§M§146713.57§00005.05§000§762.59§00395§M§301223.05§28§1165§2017-03-31 20:34:25
0.55§6abc§def§0005.05§00§ghi§jkl§123.45§678§mn§opq§5678.90123§rs§tuvw§0.12§34§xyz§6.55
$ 
$ perl replace_occurrences.pl data.txt 1-3
1007937820§L§2016-12-19§000000002§2018-02-01§2050-12-01§00395§M§146713.57§00005.05§000§762.59§00395§M§301223.05§28§1165§2017-03-31 20:34:25
0.55§6abc§def§0005.05§00§ghi§jkl§123.45§678§mn§opq§5678.90§123§rs§tuvw§0.1234§xyz§6.55
$ 
$ perl replace_occurrences.pl data.txt 2-
1007937820§L§2016-12-19§000000002§2018-02-01§2050-12-01§00395§M§146713.57§00005.05000§762.59§00395§M§301223.05§28§1165§2017-03-31 20:34:25
0.556abc§def§0005.05§00§ghi§jkl§123.45§678§mn§opq§5678.90§123§rs§tuvw§0.12§34§xyz§6.55
$ 
$ perl replace_occurrences.pl data.txt
1007937820§L§2016-12-19§000000002§2018-02-01§2050-12-01§00395§M§146713.57§00005.05§000§762.59§00395§M§301223.05§28§1165§2017-03-31 20:34:25
0.55§6abc§def§0005.05§00§ghi§jkl§123.45§678§mn§opq§5678.90§123§rs§tuvw§0.12§34§xyz§6.55
$

$ 
$ cat data.txt
1007937820§L§2016-12-19§000000002§2018-02-01§2050-12-01§00395§M§146713.57§00005.05000§762.59§00395§M§301223.0528§1165§2017-03-31 20:34:25
0.556abc§def§0005.0500§ghi§jkl§123.45§678§mn§opq§5678.90123§rs§tuvw§0.1234§xyz§6.55
$ 
$ perl -plne '$i=1; s/(\.\d\d)(?!§)/$i++ == 2 ? $1."§" : $1/eg' data.txt
1007937820§L§2016-12-19§000000002§2018-02-01§2050-12-01§00395§M§146713.57§00005.05000§762.59§00395§M§301223.05§28§1165§2017-03-31 20:34:25
0.556abc§def§0005.05§00§ghi§jkl§123.45§678§mn§opq§5678.90123§rs§tuvw§0.1234§xyz§6.55
$ 
$