seek and replace

sed -i 's/prima/dopo/g' filewithsomethingtobereplaced

# delete ALL blank lines from a file (same as "grep '.' ")

sed '/^$/d' # method 1

sed '/./!d' # method 2

sed -n 'G; s/\n/&&/; /^\([ -~]*\n\).*\n\1/d; s/\n//; h; P'

# remove all non-consecutive duplicate lines

awk '!x[$0]++' new > newfile

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