One simple way:

• Get the first line from a file with head -n 1 cdj.tsv (You already know that) or from multiple files by name like this head -q -n 1 cdj.tsv file2.tsv file3.tsv the -q will suppress printing extra headers / file names so that only the lines from the files are printed. You can use globbing * with input file names as well like this head -q -n 1 *.tsv to process all files in the current directory with .tsv extension as input.

  
  



• Then, pipe | that to tr -s ' ' '
' to process the words each on a new line i.e. one at a time ... (notice: many alternate tools can be used to do the same thing in this step even the much less efficient xargs -n 1 and the answer by @Peter Cordes in this regard is worth reading.)

  
  



• Then, pipe that to sort -u to sort and print only unique words.

  
  



• Then, to get both the words themselves and their count, pipe that to tee with wc -l in a process substitution syntax >(wc -l) and put both in a subshell syntax (...) to group the output like so:

  
  

  head -q -n 1 *.tsv | tr -s ' ' '
  
  ' | sort -u | (tee >(wc -l))
  
  

  
  



• The result from your example will look like this:

  
  

  China
  
  Country
  
  Denmark
  
  DenmarkDenmark
  
  4
  
  

  
  

Another faster way with awk or gawk:

• Start a word (field) counter, set its initial value to 1 like this i=1, limit its maximum value to the available number of fields like this i<=NF and increment it by 1 with each new field like this i++ and put all that in an awk for control statement syntax like this for ( i=1; i<=NF; i++ ).

  
  



• Then, for each field, check if the line being processed is the first line in the file like this NR==1 and if that is true check if the current field (word) hasn't occurred before and if true add its reference to an array like this !seen[$i]++ and print it with print $i and put all that in an awk if control statement syntax in an action group {...} like this { if ( NR==1 && !seen[$i]++ ) print $i }.

  
  



• Then, print the total number of unique words (fields) with print length(seen) and put it in a separate action group after the awk conditional pattern element END like this END { print length(seen) }.

  
  



• Then, Use it on a single input file like so:

  
  

  awk '{ for ( i=1; i<=NF; i++ ) { if ( NR==1 && !seen[$i]++ ) print $i }} END { print length(seen) }' cdj.tsv
  
  

  
  



• Or use it on multiple input files with FNR==1 instead of NR==1 like so:

  
  

  awk '{ for ( i=1; i<=NF; i++ ) { if ( FNR==1 && !seen[$i]++ ) print $i }} END { print length(seen) }' *.tsv
  
  

  
  



• Or use it on multiple input files with <(head -q -n 1 *.tsv) and without NR==1 or FNR==1 like so:

  
  

  awk '{ for ( i=1; i<=NF; i++ ) { if ( !seen[$i]++ ) print $i }} END { print length(seen) }' <(head -q -n 1 *.tsv)