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Top Forums Shell Programming and Scripting Removing duplicates except the last occurrence Post 302923941 by MadeInGermany on Wednesday 5th of November 2014 10:21:37 AM
Old 11-05-2014
The suggested solutions remove the sequent duplicates, keeping the first instance.
The requirement, keeping the last instance, is far more complex.
The most comprehensive solution is perl:
Code:
perl -ne '$s{$_}=++$i; if (eof()){print sort {$s{$a}<=>$s{$b}} keys %s}' file

Another one is awk | sort | cut:
Code:
awk '{ 
      x[$0] = NR
     }
 END {
      for ( l in x ) printf "%d\t%s\n", x[l], l
     }' file | sort -n | cut -f2-

Another less efficient solution would be tac | awk 'remove sequent duplicates' | tac:
Code:
tac file | awk '!($0 in S) {print; S[$0]}' | tac

This User Gave Thanks to MadeInGermany For This Post:
 

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TAC(1)									FSF								    TAC(1)

NAME
tac - concatenate and print files in reverse SYNOPSIS
tac [OPTION]... [FILE]... DESCRIPTION
Write each FILE to standard output, last line first. With no FILE, or when FILE is -, read standard input. Mandatory arguments to long options are mandatory for short options too. -b, --before attach the separator before instead of after -r, --regex interpret the separator as a regular expression -s, --separator=STRING use STRING as the separator instead of newline --help display this help and exit --version output version information and exit AUTHOR
Written by Jay Lepreau and David MacKenzie. REPORTING BUGS
Report bugs to <bug-coreutils@gnu.org>. COPYRIGHT
Copyright (C) 2002 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICU- LAR PURPOSE. SEE ALSO
The full documentation for tac is maintained as a Texinfo manual. If the info and tac programs are properly installed at your site, the command info tac should give you access to the complete manual. tac (coreutils) 4.5.3 February 2003 TAC(1)
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