Bash Script to Read INI File with Section and Key Parsing

Use a Bash script that reads the INI file line by line, skips comments and empty lines, detects sections with \[section\], and extracts key-value pairs with key=value syntax using while read and case statements.

Examples

Input[general] name=John age=30

OutputSection: general name=John age=30

Input[user] username=alice password=secret [server] ip=192.168.1.1 port=8080

OutputSection: user username=alice password=secret Section: server ip=192.168.1.1 port=8080

Input# comment line [empty] key=value [another] key2=val2

OutputSection: empty key=value Section: another key2=val2

How to Think About It

To read an INI file in Bash, treat it like a text file. Read it line by line. Ignore empty lines and comments starting with # or ;. When you see a line with square brackets, that marks a section. Save that section name. For lines with an equals sign, split into key and value. Print or store them with the current section. This way, you parse the file logically.

Algorithm

1

Open the INI file for reading line by line.

2

For each line, skip if it is empty or a comment.

3

If the line matches a section header [section], save the section name.

4

If the line contains key=value, extract key and value.

5

Print or store the section, key, and value.

6

Repeat until the end of the file.

Code

bash

#!/bin/bash
ini_file="$1"
current_section=""

shopt -s extglob
while IFS= read -r line || [[ -n "$line" ]]; do
  # Remove leading/trailing whitespace
  line="${line##+([[:space:]])}"
  line="${line%%+([[:space:]])}"

  # Skip empty lines and comments
  [[ -z "$line" || "$line" =~ ^[;#] ]] && continue

  # Check for section
  if [[ "$line" =~ ^\[(.*)\]$ ]]; then
    current_section="${BASH_REMATCH[1]}"
    echo "Section: $current_section"
  elif [[ "$line" =~ ^([^=]+)=(.*)$ ]]; then
    key="${BASH_REMATCH[1]}"
    value="${BASH_REMATCH[2]}"
    echo "$key=$value"
  fi
 done < "$ini_file"

Output

Section: general
name=John
age=30

Dry Run

Let's trace reading a simple INI file with a section and two keys.

1

Read first line

Line is '[general]', matches section pattern, current_section set to 'general', prints 'Section: general'

2

Read second line

Line is 'name=John', matches key=value pattern, prints 'name=John'

3

Read third line

Line is 'age=30', matches key=value pattern, prints 'age=30'

Step	Line	Action	Output
1	[general]	Set current_section='general'	Section: general
2	name=John	Extract key='name', value='John'	name=John
3	age=30	Extract key='age', value='30'	age=30

Why This Works

Step 1: Skip empty and comment lines

The script ignores lines that are empty or start with # or ; to avoid processing irrelevant data.

Step 2: Detect section headers

Lines matching \[section\] set the current section name, so keys can be grouped logically.

Step 3: Extract key-value pairs

Lines with key=value format are split into key and value using regex, then printed or stored.

Alternative Approaches

Using awk to parse INI

bash

awk '/^\[/{section=substr($0,2,length($0)-2)} /^[^#;].*=/{split($0,a,"="); print section ":" a[1] "=" a[2]}' file.ini

Awk is concise and fast but less readable for beginners.

Using source with sanitized INI

bash

sed -e 's/;.*//' -e 's/#.*//' -e '/^$/d' -e 's/\[\([^]]*\)\]/[\"\1\"]/g' file.ini > temp.sh
source temp.sh

Transforms INI to shell variables but requires careful sanitizing to avoid code injection.

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

Time Complexity

The script reads the file line by line once, so time grows linearly with file size.

Space Complexity

Uses constant extra space for variables; no large data structures stored.

Which Approach is Fastest?

The Bash while-read loop is simple and efficient for small to medium files; awk is faster for large files but less beginner-friendly.

Approach	Time	Space	Best For
Bash while-read loop	O(n)	O(1)	Simple scripts, beginners
Awk one-liner	O(n)	O(1)	Performance and concise parsing
Source sanitized INI	O(n)	O(1)	When INI can be safely converted to shell variables