How to compare columns of one line in same file?

Question

This is my input file :

A B B A  
A A A   
B A B A  
B B  
A A  
A B

If all columns are same, I want to print only the first column.
Otherwise, I want to print multi.

Desired output :

multi  
A  
multi  
B  
A  
multi

Can anyone help me? (I prefer awk or sed.)

Answer 1

With AWK:

awk '{ for (i = 2; i <= NF; i++) { if ($i != $1) { print "multi"; next } }; print $1 }'

This processes each line as follows:

• starting from the second field, compare each field to the first;
• if a difference is found, print "multi" and move to the next line;
• if no difference is found (the loop finishes, or is skipped entirely, e.g. for a line containing no or one field only), print the first field (and move to the next line).

Answer 2

awk/perl are the better tools for this job but you can do it with sed too:

sed -E 's/^([^[:blank:]]*)([[:blank:]]+\1)*$/\1/;t;s/.*/multi/' infile

Answer 3

$ awk '{b=$1; gsub($1,""); if (/^\s*$/) {print b} else {print "multi"}}' file         
multi
A
multi
B
A
multi