I should write a shell script able to parse a comma separated string.
An examle:
x,x,x,x,x
The problem is that the number of different 'x' is not known so how can I get avery separated x string ?
Then I should write each x on a different line of a text file.
Does a unique command exist or a script is necessary ?
 

You could parse it with awk.
echo "x,x,x,x,x" | awk -F"," '{ print NF }'
 

If the field count is unimportant but you just want to deal with the values of each field, the tr command could be used to translate commas to carriage returns.
cat comma.txt
File Server = pippo,pluto,paperino
File Server = bob,mary,bart,jim,buford

awk '{ print $NF }' comma.txt | tr "," "\012"
pippo
pluto
paperino
bob
mary
bart
jim
buford

Redirect stdout to append to a file if you want to save the results. You can process many files in a for loop.

for file in *.log ; do
awk '{ print $NF }' $file | tr "," "\012" >> outfile
done
 

Looks homeworky to me. If instructor required "pure shell" (no awk,sed ,tr ) and file contains
pippo,pluto,paperino
bob,mary,bart,jim,buford
you could submit:
Script < file
where Script is:

IFS=,
while read a
do
for f in $a
do
echo $f
done
done

for production, the above is the best way.

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