Bash Script to Find Word Frequency in File

Use tr -cs '[:alnum:]' '\n' | sort | uniq -c | sort -nr in Bash to find and display word frequency in a file.

Examples

Inputhello world hello

Output2 hello 1 world

Inputapple banana apple orange banana apple

Output3 apple 2 banana 1 orange

Input

Output

How to Think About It

To find word frequency, first split the text into words by replacing non-alphanumeric characters with new lines. Then sort the words so duplicates come together. Count each unique word's occurrences and finally sort the counts in descending order to show the most frequent words first.

Algorithm

1

Read the file content.

2

Replace all non-alphanumeric characters with new lines to isolate words.

3

Sort the list of words alphabetically.

4

Count the occurrences of each unique word.

5

Sort the counted words by frequency in descending order.

6

Display the word counts.

Code

bash

#!/bin/bash

if [ $# -ne 1 ]; then
  echo "Usage: $0 filename"
  exit 1
fi

tr -cs '[:alnum:]' '\n' < "$1" | sort | uniq -c | sort -nr | awk '{print $1, $2}'

Output

2 hello
1 world

Dry Run

Let's trace the input 'hello world hello' through the code

1

Replace non-alphanumeric with new lines

Input: 'hello world hello' -> Output: 'hello\nworld\nhello'

2

Sort words

Words: ['hello', 'hello', 'world'] sorted -> ['hello', 'hello', 'world']

3

Count unique words

'hello' appears 2 times, 'world' appears 1 time

Word	Count
hello	2
world	1

Why This Works

Step 1: Splitting words

The tr -cs '[:alnum:]' '\n' command replaces all characters except letters and numbers with new lines, isolating each word on its own line.

Step 2: Sorting words

Sorting groups identical words together so uniq -c can count consecutive duplicates.

Step 3: Counting and sorting frequency

uniq -c counts occurrences, and sort -nr sorts the counts in descending order to show the most frequent words first.

Alternative Approaches

awk script

bash

awk '{for(i=1;i<=NF;i++) freq[$i]++} END {for(word in freq) print freq[word], word}' filename | sort -nr

Uses awk to count words directly without multiple commands; simpler but less portable for complex word splitting.

grep and sort

bash

grep -oE '\w+' filename | sort | uniq -c | sort -nr

Uses grep to extract words; simpler but depends on grep supporting -o and -E options.

Complexity: O(n log n) time, O(n) space

Time Complexity

Sorting the words dominates time at O(n log n), where n is the number of words.

Space Complexity

Extra space is needed to store all words and counts, so O(n) space is used.

Which Approach is Fastest?

The tr | sort | uniq pipeline is efficient and simple; awk can be faster for very large files but may be less precise in splitting.

Approach	Time	Space	Best For
tr + sort + uniq	O(n log n)	O(n)	General use, reliable word splitting
awk counting	O(n)	O(n)	Direct counting, simpler code
grep + sort + uniq	O(n log n)	O(n)	Quick extraction if grep supports options