title: Find missing files by their number?
body: <p>I have a big list of ordered files with names like this</p>
  
  <pre><code>file_1.txt
  file_2.txt
  file_3.txt
  file_6.txt
  file_7.txt
  file_8.txt
  file_10.txt
  </code></pre>
  
  <p>In this case it is easy to see that files: <code>file_4.txt</code>,<code>file_5.txt</code> and <code>file_9.txt</code> are missing, but if i have a big list how can i find the missing files? i am just learning bash so i just know some simple examples. like this</p>
  
  <pre><code>for i in $(seq 1 1000) ;
  
  do  
    if [i not in *.txt];  then                                                                                                     
    echo $i;
  
  done
  </code></pre>
  
  <p>But this doesnt even work unless i erase the <code>if [i not in *.txt];then</code> line
  so it just writes all the numbers between 1 and 1000.
  I hope you can help me.
  Thanks in advance.</p>