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I would like to replace "CC" with "C" and "AA" with A" in a particular column of Tab delimited file (using awk probably).

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2 Answers

awk -F'\t' -vOFS='\t' '{ gsub("CC", "C", $1) ; gsub("AA", "A", $1) ; print }'

Replace $1 with the column that you wish to modify.

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In case the delimiter has to be kept, a -vOFS='\t' option may be added. –  manatwork Jun 14 '12 at 10:18
    
@manatwork Good point, added. –  Chris Down Jun 14 '12 at 10:20
    
fantastic! works as per usual!!! –  alex Jun 14 '12 at 10:51
    
Some versions of awk don't have a gsub function. How would you do it then? Can sed be used instead? –  rahmu Jun 14 '12 at 13:33
    
@rahmu - gsub() has been defined by POSIX for over 20 years, so my suggestion would be to get a version of awk that isn't downright awful ;-) –  Chris Down Jun 14 '12 at 13:40
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If you didn't have access to gsub(), but you do have access to split(), you could just create the equivalent thusly:

Given the input

AA      AA      CC      CC      AA      CC

the following awk script

BEGIN {
    OFS = "\t";
    split("1 3 5", Fields);
    split("A C", Replacements);
}
{
    for (i in Fields) {
        for (j in Replacements) {
            Replace = Replacements[j];
            sub(Replace Replace, Replace, $Fields[i]);
        }
    }
    print;
}

would produce the desired results for fields 1, 3, and 5:

A       AA      C       CC      A       CC

Even without split() it's possible if you want to hard-code the Fields and Replacements arrays in the BEGIN block.

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