Shell Programming and Scripting

Line1`abc$bn`$$

Line1: 2 "`" and 3 "$"

BEGIN {
  # if the variable 'var' has not been assigned to, assign a default value of
  # '%$`' to it.
  # The variable 'var' contains a list of characters to frequency usage for.
  if (pat=="")
    pat="%$`"

  # substitute every single character in 'var' with ' [char] ' string:
  # '%' -> ' [%] '; '$' -> ' [$] ' etc...
  gsub(/./, " [&] ", pat)

  # split string in 'pat' by ' ' and store results in array 'patA' (parN - holds the number of entries the patA array):
  # patA[1]='[%]'; patA[2]='[$]' etc....
  patN=split(pat, patA, " ")
}
{
  # print the line number - NF holds the current line number 
  printf("Line %d:", FNR)

  # iterate through ALL the entries ( 1 ---> patN) in patA array
  # for every entry in the array, substitute (gsub) the current entry if found in the current line ($0) with 
  # the empty string "" (nothing). The substitution/gsub returns the NUMBER of the successful substitutions
  # This is the number a particular character/string/regex appears in a given string ($0 - your record/line).
  for(i=1; i <= patN; i++)
     printf(" %d '%s' %s", gsub(patA[i], "", $0), patA[i], (i==patN) ? "\n" : "")
}