Shell Programming and Scripting

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$ cat -n mylog_1.txt
     1  01/05/2017 10:23:41 [ABCD-22357$0]: file.log.38: database error, MODE=SINGLE, LEVEL=critical, STATE: 01170255 (mode main
     2  something else
     3  over here
     4  01/05/2017 10:23:41 [ABCD-22357$0]: file.log.38: database error, MODE=SINGLE, LEVEL=critical, BLAH: 12345678 (mode main
     5  some other stuff
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$ cat -n process_log.pl
     1  #!/usr/bin/perl -w
     2  # ------------------------------------------------------------------------------
     3  # Name : process_log.pl
     4  # Desc : A short and quick Perl program to process log files. It performs
     5  #        rudimentary input validation and error handling.
     6  # Usage: perl process_log.pl <log_file>
     7  # ------------------------------------------------------------------------------
     8  use strict;
     9
    10  # Print usage and quit if incorrect number of parameters were passed.
    11  if ($#ARGV != 0) {
    12      print "Usage: perl process_log.pl <log_file>\n";
    13      exit 1;
    14  }
    15
    16  # Set the file name. Hopefully it can be opened!
    17  my $file = $ARGV[0];
    18
    19  # Open file, loop through each line and process, close file
    20  open(FH, "<", $file) or die "Can't open $file: $!";
    21  while (<FH>) {
    22      # Remove the end of line character
    23      chomp;
    24      if (/(STATE|BLAH):\s+(\d+)/) {
    25          print $2, "\n";
    26      }
    27  }
    28  close(FH) or die "Can't close $file: $!";
    29
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$ # Test with no parameters
$ perl process_log.pl
Usage: perl process_log.pl <log_file>
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$ # Test with a file name that cannot be found or opened
$ perl process_log.pl does_not_exist.txt
Can't open does_not_exist.txt: No such file or directory at process_log.pl line 20.
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$ # Test with the correct file
$ perl process_log.pl mylog_1.txt
01170255
12345678
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