title: Tcl. Replace string in file
body: <p>There is a command in tcl which allows to create new string on the basis of existing by replacement :</p>
  
  <pre><code>string map ?-nocase? mapping string
  </code></pre>
  
  <p>Whether there is in tcl a command allowing to change the existing string?
  For example:</p>
  
  <pre><code>set string1 abcabcabc
  </code></pre>
  
  <p>By using some command replace a letter "a" by "0" to get string1 with value 0bc0bc0bc</p>