Bash Script to Read YAML File Easily

Use a Bash script with grep and sed to extract values from a YAML file, for example: value=$(grep '^key:' file.yaml | sed 's/^key:[[:space:]]*//') reads the value of 'key'.

Examples

Inputfile.yaml content: name: Alice

OutputAlice

Inputfile.yaml content: user: bob age: 30

Outputbob

Inputfile.yaml content: empty_key:

Output

How to Think About It

To read a YAML file in Bash, think of it as a text file where each line has a key and a value separated by a colon. You can find the line starting with the key you want using grep, then remove the key and colon to get the value using sed or similar tools.

Algorithm

1

Get the YAML file path and the key to read.

2

Search the file for the line starting with the key followed by a colon.

3

Extract the part after the colon, trimming spaces.

4

Return or print the extracted value.

Code

bash

#!/bin/bash

file="file.yaml"
key="name"

value=$(grep "^$key:" "$file" | sed -e "s/^$key:[[:space:]]*//")
echo "$value"

Output

Alice

Dry Run

Let's trace reading the key 'name' from file.yaml containing 'name: Alice'.

1

Search for key line

grep '^name:' file.yaml returns 'name: Alice'

2

Extract value

sed removes 'name: ' leaving 'Alice'

3

Print value

echo prints 'Alice'

Step	Command Output
grep '^name:' file.yaml	name: Alice
sed 's/^name:[[:space:]]*//'	Alice
echo	Alice

Why This Works

Step 1: Find the key line

The grep command looks for the line starting with the key and a colon to isolate the correct line.

Step 2: Remove the key and colon

The sed command deletes the key and colon, leaving only the value part.

Step 3: Output the value

The script prints the extracted value so you can use it in your Bash script.

Alternative Approaches

Using yq command-line tool

bash

value=$(yq e '.name' file.yaml)
echo "$value"

Requires installing yq but handles complex YAML safely and easily.

Using awk to parse YAML

bash

value=$(awk -F": " '/^name:/ {print $2}' file.yaml)
echo "$value"

Simple and fast for flat YAML but less flexible for nested structures.

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?

Using grep and sed is fast for simple YAML; yq is slower but safer for complex files.

Approach	Time	Space	Best For
grep + sed	O(n)	O(1)	Simple flat YAML
yq tool	O(n)	O(1)	Complex or nested YAML
awk	O(n)	O(1)	Simple key-value extraction