freq - print histogram of character frequencies

Freq  reads  the given files (default standard input) and prints histograms of the character frequencies.
       By default, freq counts each byte as a character; under the -r option it instead  counts  UTF  sequences,
       that is, runes.

       Each  non-zero  entry  of  the  table  is printed preceded by the byte value, in decimal, octal, hex, and
       Unicode character (if printable).  If any options are given, the -d, -x, -o, -c flags specify a subset of
       value formats: decimal, hex, octal, and character, respectively.

       freq - print histogram of character frequencies

utf(7), wc(1)

                                                                                                    FREQ(1plan9)

/src/cmd/freq.c

freq [ -dxocr ] [ file...  ]