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gawk: Readfile Function

 10.2.8 Reading a Whole File at Once
 Often, it is convenient to have the entire contents of a file available
 in memory as a single string.  A straightforward but naive way to do
 that might be as follows:
      function readfile1(file,    tmp, contents)
          if ((getline tmp < file) < 0)
          contents = tmp RT
          while ((getline tmp < file) > 0)
              contents = contents tmp RT
          return contents
    This function reads from 'file' one record at a time, building up the
 full contents of the file in the local variable 'contents'.  It works,
 but is not necessarily efficient.
    The following function, based on a suggestion by Denis Shirokov,
 reads the entire contents of the named file in one shot:
      # readfile.awk --- read an entire file at once
      function readfile(file,     tmp, save_rs)
          save_rs = RS
          RS = "^$"
          getline tmp < file
          RS = save_rs
          return tmp
    It works by setting 'RS' to '^$', a regular expression that will
 never match if the file has contents.  'gawk' reads data from the file
 into 'tmp', attempting to match 'RS'.  The match fails after each read,
 but fails quickly, such that 'gawk' fills 'tmp' with the entire contents
 of the file.  (⇒Records for information on 'RT' and 'RS'.)
    In the case that 'file' is empty, the return value is the null
 string.  Thus, calling code may use something like:
      contents = readfile("/some/path")
      if (length(contents) == 0)
          # file was empty ...
    This tests the result to see if it is empty or not.  An equivalent
 test would be 'contents == ""'.
    ⇒Extension Sample Readfile for an extension function that also
 reads an entire file into memory.
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