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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 SUSE

uniq

UNIQ(1) 							   User Commands							   UNIQ(1)

NAME

       uniq - report or omit repeated lines

SYNOPSIS

       uniq [OPTION]... [INPUT [OUTPUT]]

DESCRIPTION

       Discard all but one of successive identical lines from INPUT (or standard input), writing to OUTPUT (or standard output).

       Mandatory arguments to long options are mandatory for short options too.

       -c, --count
	      prefix lines by the number of occurrences

       -d, --repeated
	      only print duplicate lines

       -D, --all-repeated[=delimit-method]
	      print all duplicate lines delimit-method={none(default),prepend,separate} Delimiting is done with blank lines.

       -f, --skip-fields=N
	      avoid comparing the first N fields

       -i, --ignore-case
	      ignore differences in case when comparing

       -s, --skip-chars=N
	      avoid comparing the first N characters

       -u, --unique
	      only print unique lines

       -z, --zero-terminated
	      end lines with 0 byte, not newline

       -w, --check-chars=N
	      compare no more than N characters in lines

       --help display this help and exit

       --version
	      output version information and exit

       A field is a run of blanks (usually spaces and/or TABs), then non-blank characters.  Fields are skipped before chars.

       Note:  'uniq'  does  not  detect  repeated  lines unless they are adjacent.  You may want to sort the input first, or use `sort -u' without
       `uniq'.

AUTHOR

       Written by Richard M. Stallman and David MacKenzie.

REPORTING BUGS

       Report uniq bugs to bug-coreutils@gnu.org
       GNU coreutils home page: <http://www.gnu.org/software/coreutils/>
       General help using GNU software: <http://www.gnu.org/gethelp/>

COPYRIGHT

       Copyright (C) 2009 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
       This is free software: you are free to change and redistribute it.  There is NO WARRANTY, to the extent permitted by law.

SEE ALSO

       The full documentation for uniq is maintained as a Texinfo manual.  If the info and uniq programs are properly installed at your site,  the
       command

	      info coreutils 'uniq invocation'

       should give you access to the complete manual.

GNU coreutils 7.1						     July 2010								   UNIQ(1)