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Rewriting GNU uniq in awk

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Top Forums Shell Programming and Scripting Rewriting GNU uniq in awk
# 8  
Old 10-23-2012
Quote:
Originally Posted by alister
What does the data look like? Does it adhere to some format? Does it contain whitespace? Are certain characters guaranteed to appear? Are certain characters guaranteed to not appear? Knowing what we're dealing with might suggest alternative approaches.
Each line has a number, right aligned with leading spaces, which takes up the first 16 characters, a space, then an unquoted string of variable length that can include any characters. There is another version that is sometimes used which has a 32 character MD5 hash, followed again by a space then the string.

The data is sorted so a simple comparison with the previous line is enough to find a match. It could consist of any number of lines, from just a few to tens of thousands, similarly there could be any number with a duplicated first field. The initial number or hash is used to group different strings, which will always be unique. The lines in a duplicated group are then piped into a "while read" loop for processing.
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LEARN ABOUT OSX

uniq

UNIQ(1) 						    BSD General Commands Manual 						   UNIQ(1)

NAME

     uniq -- report or filter out repeated lines in a file

SYNOPSIS

     uniq [-c | -d | -u] [-i] [-f num] [-s chars] [input_file [output_file]]

DESCRIPTION

     The uniq utility reads the specified input_file comparing adjacent lines, and writes a copy of each unique input line to the output_file.	If
     input_file is a single dash ('-') or absent, the standard input is read.  If output_file is absent, standard output is used for output.  The
     second and succeeding copies of identical adjacent input lines are not written.  Repeated lines in the input will not be detected if they are
     not adjacent, so it may be necessary to sort the files first.

     The following options are available:

     -c      Precede each output line with the count of the number of times the line occurred in the input, followed by a single space.

     -d      Only output lines that are repeated in the input.

     -f num  Ignore the first num fields in each input line when doing comparisons.  A field is a string of non-blank characters separated from
	     adjacent fields by blanks.  Field numbers are one based, i.e., the first field is field one.

     -s chars
	     Ignore the first chars characters in each input line when doing comparisons.  If specified in conjunction with the -f option, the
	     first chars characters after the first num fields will be ignored.  Character numbers are one based, i.e., the first character is
	     character one.

     -u      Only output lines that are not repeated in the input.

     -i      Case insensitive comparison of lines.

ENVIRONMENT

     The LANG, LC_ALL, LC_COLLATE and LC_CTYPE environment variables affect the execution of uniq as described in environ(7).

EXIT STATUS

     The uniq utility exits 0 on success, and >0 if an error occurs.

COMPATIBILITY

     The historic +number and -number options have been deprecated but are still supported in this implementation.

SEE ALSO

     sort(1)

STANDARDS

     The uniq utility conforms to IEEE Std 1003.1-2001 (``POSIX.1'') as amended by Cor. 1-2002.

HISTORY

     A uniq command appeared in Version 3 AT&T UNIX.

BSD
								   July 3, 2004 							       BSD