wc and uniq

Counting Lines, Words, and Characters

wc reports line, word, and byte counts. Passing -l, -w, or -c restricts the output to just that one count, which is easier to use in scripts than parsing the default three-column output.

Note: Redirecting the file with < instead of passing it as an argument avoids the filename being printed alongside the count.

Example: Counting Lines, Words, and Characters

#!/bin/bash
printf "one two\nthree\n" > sample.txt
echo "lines: $(wc -l < sample.txt)"
echo "words: $(wc -w < sample.txt)"
rm -f sample.txt

Removing Adjacent Duplicates

uniq collapses runs of identical consecutive lines into one. It does NOT remove duplicates scattered non-adjacently through the file, so input is usually sorted first to bring duplicates together.

Example: Removing Adjacent Duplicates

#!/bin/bash
printf "a\na\nb\na\nb\nb\n" > raw.txt
echo "uniq alone (misses non-adjacent duplicates):"
uniq raw.txt
echo "sort then uniq (all duplicates collapsed):"
sort raw.txt | uniq
rm -f raw.txt

Counting Occurrences

uniq -c prefixes each line of output with the number of consecutive times it appeared, turning a list of items into a frequency table.

Example: Counting Occurrences

#!/bin/bash
printf "apple\nbanana\napple\napple\nbanana\n" | sort | uniq -c

Finding the Most Frequent Items

Chaining sort | uniq -c | sort -n sorts items, counts consecutive duplicates, then sorts by that count numerically, producing a ranked frequency list, a very common one-liner.

Example: Finding the Most Frequent Items

#!/bin/bash
printf "a\nb\na\nc\na\nb\n" | sort | uniq -c | sort -n