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Top Forums Shell Programming and Scripting perl/shell need help to remove duplicate lines from files Post 302483206 by DGPickett on Friday 24th of December 2010 10:47:16 AM
Old 12-24-2010
OK, A. the key is not the whole line, and B. duplicates across files are bad, two complications. Reporting the duplicate means a definition of the original, expecially for non-key data.
  • If the lines have identical keys and not identical payload (fields not keys), then will file name order and order in file pick a winner?
  • We need to survey all files for duplicate keys, then extract the unique and winners to load, and the losers to report. Think of them as two important products, not picking favorites. While most days there may be no duplicates, if one day there are tons, you still want it to blast through.
  • There are two approaches to dealing with duplicate filtering. You can save every key in an associative array (magic box that recalls by value, but may not be robust in speed and stability with huge volume) or you can sort in key, priority order (more traditional and quite robust if you have the disk space. Store just the last key, process the first of every key and log the others. Worked great on tape in 1960 with 16K or RAM! :-)
  • Tagging the duplicates by original file means adding the file name to every record, possible but a bit of a luxury if not needed.
 

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sort(1) 						      General Commands Manual							   sort(1)

Name
       sort - sort file data

Syntax
       sort [options] [-k keydef] [+pos1[-pos2]] [file...]

Description
       The  command  sorts  lines  of  all the named files together and writes the result on the standard output.  The name `-' means the standard
       input.  If no input files are named, the standard input is sorted.

Options
       The default sort key is an entire line.	Default ordering is lexicographic by  bytes  in  machine  collating  sequence.	 The  ordering	is
       affected globally by the following options, one or more of which may appear.

       -b	   Ignores leading blanks (spaces and tabs) in field comparisons.

       -d	   Sorts data according to dictionary ordering:  letters, digits, and blanks only.

       -f	   Folds uppercase to lowercase while sorting.

       -i	   Ignore characters outside the ASCII range 040-0176 in nonnumeric comparisons.

       -k keydef   The	keydefargument	is  a key field definition. The format is field_start, [field_end] [type], where field_start and field_end
		   are the definition of the restricted search key, and type is a modifier from the option list [bdfinr]. These modifiers have the
		   functionality, for this key only, that their command line counter-parts have for the entire record.

       -n	   Sorts fields with numbers numerically.  An initial numeric string, consisting of optional blanks, optional minus sign, and zero
		   or more digits with optional decimal point, is sorted by arithmetic value.  (Note that -0 is taken to be equal to 0.)  Option n
		   implies option b.

       -r	   Reverses the sense of comparisons.

       -tx	   Uses specified character as field separator.

       The  notation  +pos1 -pos2 restricts a sort key to a field beginning at pos1 and ending just before pos2.  Pos1 and pos2 each have the form
       m.n, optionally followed by one or more of the options bdfinr, where m tells a number of fields to skip from the beginning of the line  and
       n tells a number of characters to skip further.	If any options are present they override all the global ordering options for this key.	If
       the b option is in effect n is counted from the first nonblank in the field; b is attached independently to pos2.  A missing .n means .0; a
       missing	-pos2  means the end of the line.  Under the -tx option, fields are strings separated by x; otherwise fields are nonempty nonblank
       strings separated by blanks.

       When there are multiple sort keys, later keys are compared only after all earlier keys compare equal.  Lines that otherwise  compare  equal
       are ordered with all bytes significant.

       These are additional options:

       -c	   Checks sorting order and displays output only if out of order.

       -m	   Merges previously sorted data.

       -o name	   Uses specified file as output file.	This file may be the same as one of the inputs.

       -T dir	   Uses specified directory to build temporary files.

       -u	   Suppresses all duplicate entries.  Ignored bytes and bytes outside keys do not participate in this comparison.

Examples
       Print in alphabetical order all the unique spellings in a list of words.  Capitalized words differ from uncapitalized.
	       sort -u +0f +0 list

       Print the password file, sorted by user id number (the 3rd colon-separated field).
	       sort -t: +2n /etc/passwd

       Print the first instance of each month in an already sorted file of (month day) entries.  The options -um with just one input file make the
       choice of a unique representative from a set of equal lines predictable.
	       sort -um +0 -1 dates

Restrictions
       Very long lines are silently truncated.

Diagnostics
       Comments and exits with nonzero status for various trouble conditions and for disorder discovered under option c.

Files
       /usr/tmp/stm*, /tmp/*	first and second tries for temporary files

See Also
       comm(1), join(1), rev(1), uniq(1)

																	   sort(1)
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