Read filter expression from file

The filter expression can be read from file. E.g.: 

  1. # cat filter
  2. port 80

“-F file“ option can be used to read filter from file instead of command line: 

  1. # tcpdump -F filter
  2. tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
  3. listening on enp0s3, link-type EN10MB (Ethernet), capture size 262144 bytes
  4. ......

The code is here: 

  1. ......
  2. if (infile)
  3.     cmdbuf = read_infile(infile);
  4. else
  5.     cmdbuf = copy_argv(&argv[optind]);
  6. ......