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I have the following data:

ID Affection rs3117294 rs2747453 rs2747454 rs2747457 rs3131888
D0024949 0 C_C A_G A_G A_A A_G
D0024302 0 A_C A_A A_G A_A A_A
D0023151 0 C_C A_G A_A A_A G_G
D0022042 0 A_C A_A G_G A_A A_A
D0021275 0 C_C A_G A_G A_A A_G
D0021163 0 A_A A_A G_G A_A A_A
D0020795 0 A_A A_A G_G A_C A_G
D0020691 0 A_A A_A G_G A_C A_G
D0019121 0 A_A A_A G_G C_C G_G

I want to make the underscore a space, so that C_C to be C C.

How can I do that? Please make the code general to apply it to the whole data I have.

I got the following from someone "not my code" sed '1d' plink.raw | sed 's/_/ /g' > plinkv2.raw, but it gave me empty cells the data is not complete.

GNU sed:

sed -itmp 's/(w)_(w)/1 2/g' file

This will overwrite file and save a backup of original to file.tmp.

POSIX sed:

sed 's/([[:alpha:]])_([[:alpha:]])/1 2/g' file > file2

You have to redirect to another file. Copy file2 to the original if that's what you want.

Both use the concept of "back-references". Surrounding text with (..) in the pattern makes it available in the substitution with 1, 2, etc.

Please find the below command and output

it replaces _ with spaces through out the file

awk 'gsub("_"," ",$0);print $0' j.txt 
D0024949 0 C C A G A G A A A G
D0024302 0 A C A A A G A A A A
D0023151 0 C C A G A A A A G G
D0022042 0 A C A A G G A A A A
D0021275 0 C C A G A G A A A G
D0021163 0 A A A A G G A A A A
D0020795 0 A A A A G G A C A G
D0020691 0 A A A A G G A C A G
D0019121 0 A A A A G G C C G G

IF want it to be replace only first match

sed "s/_/ /1" inputfile

Let us know for any clarification kindly provide the proper input and output