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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)
              return
 
          contents = tmp RT
          while ((getline tmp < file) > 0)
              contents = contents tmp RT
 
          close(file)
          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
          close(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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