$
$ # The Perl program to modify multi-line text in multiple files
$
$ cat -n modify_multiline.pl
     1  #!/usr/bin/perl -w
     2  use strict;
     3  my @files = qw (file1 file2 file3);   # file list to modify
     4  my $text = <<"EOF";                   # multi-line static text
     5  My multi-line
     6  static text
     7  over here
     8  EOF
     9  foreach my $old (@files) {
    10    my $new = "$old.new";
    11    open(OLD, "<", $old) or die "Can't open $old: $!";
    12    open(NEW, ">", $new) or die "Can't open $new: $!";
    13    my $on = 1;                         # set printing on at the outset
    14    while (<OLD>) {
    15      if (/^---\+\+ Details/) {         # matched pattern starts
    16        print NEW $_;                   # print this line
    17        $on = 0;                        # set printing off
    18      } elsif (/^---\+\+ More info/) {  # matched pattern ends
    19        print NEW $text;                # print static text
    20        $on = 1;                        # set printing on
    21      }
    22      print NEW $_ if $on;              # print if printing on
    23    }
    24    close(OLD) or die "Can't close $old: $!";
    25    close(NEW) or die "Can't close $new: $!";
    26    rename($old, "$old.bak") or die "Can't rename $old to $old.bak: $!";
    27    rename($new, $old) or die "Can't rename $new to $old: $!";
    28  }
$
$ # Original files before modification
$
$ cat -n file1
     1  ---++ Title
     2  FILE1
     3
     4  ---++ Summary
     5  blah
     6
     7  ---++ Details
     8  Here is the multiline
     9  block
    10  of text I
    11  wish
    12  to
    13  replace that will
    14  be different
    15  in
    16  every file
    17
    18  ---++ More info
    19  blah
$
$ cat -n file2
     1  ---++ Title
     2  FILE2
     3
     4  ---++ Summary
     5  blah
     6
     7  ---++ Details
     8  Here is the multiline
     9  block
    10  of text I
    11  wish
    12  to
    13  replace that will
    14  be different
    15  in
    16  every file
    17
    18  ---++ More info
    19  blah
$
$ cat -n file3
     1  ---++ Title
     2  FILE3
     3
     4  ---++ Summary
     5  blah
     6
     7  ---++ Details
     8  Here is the multiline
     9  block
    10  of text I
    11  wish
    12  to
    13  replace that will
    14  be different
    15  in
    16  every file
    17
    18  ---++ More info
    19  blah
$
$ # Now run the Perl program
$
$ perl modify_multiline.pl
$
$ # Check modified files
$
$ cat -n file1
     1  ---++ Title
     2  FILE1
     3
     4  ---++ Summary
     5  blah
     6
     7  ---++ Details
     8  My multi-line
     9  static text
    10  over here
    11  ---++ More info
    12  blah
$
$ cat -n file2
     1  ---++ Title
     2  FILE2
     3
     4  ---++ Summary
     5  blah
     6
     7  ---++ Details
     8  My multi-line
     9  static text
    10  over here
    11  ---++ More info
    12  blah
$
$ cat -n file3
     1  ---++ Title
     2  FILE3
     3
     4  ---++ Summary
     5  blah
     6
     7  ---++ Details
     8  My multi-line
     9  static text
    10  over here
    11  ---++ More info
    12  blah
$
$ # Check backup files
$
$ cat -n file1.bak
     1  ---++ Title
     2  FILE1
     3
     4  ---++ Summary
     5  blah
     6
     7  ---++ Details
     8  Here is the multiline
     9  block
    10  of text I
    11  wish
    12  to
    13  replace that will
    14  be different
    15  in
    16  every file
    17
    18  ---++ More info
    19  blah
$
$ cat -n file2.bak
     1  ---++ Title
     2  FILE2
     3
     4  ---++ Summary
     5  blah
     6
     7  ---++ Details
     8  Here is the multiline
     9  block
    10  of text I
    11  wish
    12  to
    13  replace that will
    14  be different
    15  in
    16  every file
    17
    18  ---++ More info
    19  blah
$
$ cat -n file3.bak
     1  ---++ Title
     2  FILE3
     3
     4  ---++ Summary
     5  blah
     6
     7  ---++ Details
     8  Here is the multiline
     9  block
    10  of text I
    11  wish
    12  to
    13  replace that will
    14  be different
    15  in
    16  every file
    17
    18  ---++ More info
    19  blah
$
$