Bash Script to Split File into Parts Easily

Use the Bash command split -l 100 filename prefix to split a file into parts each containing 100 lines, where filename is your file and prefix is the output file prefix.

Examples

Inputfile.txt with 250 lines, split into parts of 100 lines each

OutputCreates files prefixaa (lines 1-100), prefixab (lines 101-200), prefixac (lines 201-250)

Inputfile.txt with 50 lines, split into parts of 20 lines each

OutputCreates files prefixaa (lines 1-20), prefixab (lines 21-40), prefixac (lines 41-50)

Inputfile.txt with 10 lines, split into parts of 15 lines each

OutputCreates one file prefixaa with all 10 lines

How to Think About It

To split a file into parts, decide how many lines each part should have. Then use the split command with the -l option to divide the file into smaller files each containing that many lines. The command automatically names the output files with a prefix and suffix.

Algorithm

1

Get the input file name and desired number of lines per part.

2

Use the split command with the -l option and a prefix for output files.

3

The split command creates multiple files each with the specified number of lines.

4

Check the output files to confirm the split.

Code

bash

#!/bin/bash

input_file="file.txt"
lines_per_part=100
output_prefix="part_"

split -l "$lines_per_part" "$input_file" "$output_prefix"
echo "File split into parts with prefix '$output_prefix'"

Output

File split into parts with prefix 'part_'

Dry Run

Let's trace splitting a file with 250 lines into parts of 100 lines each.

1

Set variables

input_file = 'file.txt', lines_per_part = 100, output_prefix = 'part_'

2

Run split command

split -l 100 file.txt part_

3

Resulting files

part_aa (lines 1-100), part_ab (lines 101-200), part_ac (lines 201-250)

Output File	Lines Included
part_aa	1-100
part_ab	101-200
part_ac	201-250

Why This Works

Step 1: Using split command

The split command divides a file into smaller files based on line count or size.

Step 2: Option -l for lines

The -l option tells split how many lines each output file should contain.

Step 3: Output file naming

Split names output files by adding suffixes like 'aa', 'ab' to the given prefix.

Alternative Approaches

Split by byte size

bash

split -b 1M file.txt part_

Splits file into parts each 1 megabyte in size instead of line count; useful for binary files.

Using csplit for pattern-based splitting

bash

csplit file.txt '/pattern/' '{*}'

Splits file at lines matching a pattern; more flexible but complex.

Manual split with awk

bash

awk 'NR%100==1 {file=sprintf("part_%03d.txt", ++i)} {print > file}' file.txt

Splits file every 100 lines using awk; more control but longer code.

Complexity: O(n) time, O(1) space

Time Complexity

The split command reads the entire file once, so time grows linearly with file size.

Space Complexity

Split writes output files directly without loading the whole file into memory, so space is constant.

Which Approach is Fastest?

Using the built-in split command is fastest and simplest compared to manual scripting.

Approach	Time	Space	Best For
split -l	O(n)	O(1)	Simple line-based splitting
split -b	O(n)	O(1)	Splitting by file size
csplit	O(n)	O(1)	Pattern-based splitting
awk manual	O(n)	O(1)	Custom splitting logic