title: p4 tag lots of files from command line
body: <p>Is there a way to tag with perforce a sizable number of files?</p>
  
  <p>Our depot (more precisely, the part of my company's shared depot where our code resides) has over 20k files, and our build process needs to tag a subset, say in the 3k to 7k files range.</p>
  
  <p>There is no changelist with the files to tag, just a plain text list.  We cannot feed the whole list to the CLI p4, as the command line would be too long. We currently tag directory by directory, but this involves a lot of p4 invocations and is a bit slow.</p>
  
  <p>Is there a way to tell p4 to tag all files listed "in this file"?  Note that to create a changelist I would be faced with the same problem.</p>