Otago Study Group SYSKA

tr or “translate or delete characters” is a super useful program on the command line.

My most common usage is to convert delimiters in files, such as tab separated to comma separated:

tr "\t" "," < tab_separated_file.tsv

or to work out how many columns I have by taking the first line of a file and converting the delimiters to new lines and then counting the number of lines:

echo -e "col1\tcol2\tcol3" > file.tsv
head -n 1 file.tsv | tr "\t" "\n" | wc -l

## 3

Or if you want to remove whitespace padding from a fixed width output:

echo 'some      fixed   width   text' | tr -s ' ' 

## some fixed width text

One super useful feature for the genetically inclined is mapping characters to be changed, for instance creating the complement for strand of DNA:

echo ACGTGGTAACT | tr ACGT TGCA

## TGCACCATTGA

tr takes the characters by index in the first argument and will translate them to the same indexed character in the second argument.