Bash Script to Sort Lines in a File Easily

Use the Bash command sort filename to sort lines in a file alphabetically, or write a script with sort inputfile -o outputfile to save sorted lines.

Examples

Inputbanana apple cherry

Outputapple banana cherry

Inputdog cat bird ant

Outputant bird cat dog

Input

Output

How to Think About It

To sort lines in a file, think of reading each line and arranging them in order from A to Z. The Bash sort command does this automatically by comparing lines and putting them in sequence.

Algorithm

1

Get the filename as input.

2

Read all lines from the file.

3

Compare lines alphabetically.

4

Arrange lines in ascending order.

5

Output the sorted lines to the screen or save to a file.

Code

bash

#!/bin/bash
# Script to sort lines in a file
input_file="$1"
output_file="$2"

if [[ ! -f "$input_file" ]]; then
  echo "File not found: $input_file"
  exit 1
fi

sort "$input_file" -o "$output_file"
echo "Sorted lines saved to $output_file"

Output

Sorted lines saved to sorted.txt

Dry Run

Let's trace sorting the file with lines: dog, cat, bird, ant

1

Check if input file exists

Input file 'animals.txt' exists.

2

Sort lines

Lines before sort: dog, cat, bird, ant Lines after sort: ant, bird, cat, dog

3

Save output

Sorted lines saved to 'sorted.txt'

Original Line	Sorted Position
dog	4
cat	3
bird	2
ant	1

Why This Works

Step 1: Using the sort command

The sort command reads all lines and compares them alphabetically.

Step 2: Saving sorted output

Using -o outputfile writes the sorted lines back to a file instead of printing to screen.

Alternative Approaches

Sort and print to screen

bash

#!/bin/bash
input_file="$1"
if [[ ! -f "$input_file" ]]; then
  echo "File not found"
  exit 1
fi
sort "$input_file"

This prints sorted lines to the terminal without saving.

Sort with unique lines

bash

#!/bin/bash
input_file="$1"
if [[ ! -f "$input_file" ]]; then
  echo "File not found"
  exit 1
fi
sort -u "$input_file" -o "$input_file"

Sorts and removes duplicate lines, saving back to the same file.

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

Time Complexity

Sorting lines requires comparing them, which takes O(n log n) time where n is the number of lines.

Space Complexity

The sort command may use extra memory proportional to the number of lines to hold them during sorting.

Which Approach is Fastest?

Using the built-in sort command is fastest and most efficient compared to manual sorting in scripts.

Approach	Time	Space	Best For
sort command with -o	O(n log n)	O(n)	Saving sorted lines to a file
sort command printing to screen	O(n log n)	O(n)	Quick sorting without saving
sort -u for unique lines	O(n log n)	O(n)	Sorting and removing duplicates