Shell Programming and Scripting

File Format

U	A	45	B
N	A	78	M	
M 	A	98	O

U	A	45	B	45
N	A	78	M	78
M 	A	98	O	98

awk '{if($2=="A")print $1" " $2" " $3" " $4" " $3;else print $1" " $2" " $3" " $4}' filename

awk '{for(i=1;i<=NF;++i)if($i=="A")print $0"\t"$(i+1)}' inputfile
U    A    45    B    45
N    A    78    M    78
M    A    98    O    98

awk '{for(i=1;i<=NF;++i)if($i=="A")print $0,$(i+1)}' inputfile

awk '{sub($0,$0 FS $3)}1' file

awk '{for(i=1;i<=NF;++i)if($i=="A")print $0,$(i+1)}' inputfile

for(i=1;i<=NF;++i)--> The "for loop" goes through all the columns/fields (NF=last column number, in this case NF=4) for every line. 

if($i=="A") --> Within the "for loop" is present the condition that says, when I pass for column i, and is found that column i has 
a value ="A" ($i="A"),

print $0,$(i+1) --> then, inmediately print the whole line ($0), followed by an space "," and the value after column i =$(i+1)

awk '{for(i=1;i<=NF;++i)if($i=="A")print "string A, was found in column " i}' inputfile