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find . -type f | perl -ne 'print $1 if m/\.([^.\/]+)$/' | sort -u
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find "$directory" -type f -name "*.in"
# Example: To find all csv files in the current directory and its sub-directories, use:
find . -type f -name '*.csv'
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find . -type f | rev | cut -d. -f1 | rev | tr '[:upper:]' '[:lower:]' | sort | uniq --count | sort -rn