Bash – find files with non-zero size in shell

do {
  local $^I='.bak'; # see perlvar(1)
  local @ARGV=("file");
  while(<>){
    s/<value>/<value>/ig;
    print;
  }
};

Beware though: $^I like perl's -i isn't crashproof.

This will put your text into your variable without needing to escape the quotes. It will also handle unbalanced quotes (apostrophes, i.e. '). Putting quotes around the sentinel (EOF) prevents the text from undergoing parameter expansion. The -d'' causes it to read multiple lines (ignore newlines). read is a Bash built-in so it doesn't require calling an external command such as cat.

IFS='' read -r -d '' String <<"EOF"
<?xml version="1.0" encoding='UTF-8'?>
 <painting>
   <img src="madonna.jpg" alt='Foligno Madonna, by Raphael'/>
   <caption>This is Raphael's "Foligno" Madonna, painted in
   <date>1511</date>-<date>1512</date>.</caption>
 </painting>
EOF