Jinjagen 🌀

A CLI tool for generating files using Jinja2 templates with smart delimiters and dynamic data.

Features ✨

• Auto-detects delimiters for code/file types (e.g., # for Python/Shell, /*% for C/JS).
• Supports JSON/YAML data inputs for dynamic templates.
• Lightweight CLI with stdin/stdout support.

☕ Support

If you find this project helpful, consider supporting me:

Usage 🛠️

Basic Example

Generate a file from a template and JSON data:

python -m jinjagen template.txt.j2 output.txt -d data.json

Real-World Use Case: Bash Script Generation

1. Template (backup.sh.j2):

#!/bin/bash
#jinjagen: -D#
BACKUP_PATHS=(#% for path in backup_paths %# "#{ path }#" #% endfor %#)

#% if notify.enabled %#
EMAIL="#{ notify.email }#"
#% endif %#

2. Data (config.json):

{
  "backup_paths": ["/home/user/docs", "/etc/nginx"],
  "notify": { "enabled": true, "email": "admin@example.com" }
}

3. Generate Script:

python -m jinjagen backup.sh.j2 backup.sh -d config.json

Output (backup.sh):

#!/bin/bash
BACKUP_PATHS=( "/home/user/docs"  "/etc/nginx" )
EMAIL="admin@example.com"

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Advanced Options ⚙️

Flag	Description	Example
-d/--data FILE	Load variables from JSON/YAML.	-d config.yml
-D/--delimiters	Force delimiters (#, /, or .).	-D# (for Bash/Python)
-t/--templates	Specify template directory.	-t ./templates
INPUT - OUTPUT	Use - for stdin/stdout.	template.j2 - -d data.json

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Delimiters Explained 🔠

Jinjagen automatically adapts Jinja2 delimiters to avoid conflicts with different file types. You can also override this behavior manually.

Default Behavior (Auto-Detection)

The tool guesses delimiters based on file extensions:

File Type	Example Extensions	Delimiters
C/JS/Java	.c, .js, .java	/*% %*/ (blocks) /*{ }*/ (variables)
Python/Shell	.py, .sh, .yaml	#% %# (blocks) #{ }# (variables)
Generic/Other	.txt, .html	{% %} (blocks) {{ }} (variables)

Example: For a .c file, Jinjagen uses /_% if x %_/instead of{% if x %}.

Manual Override

Force specific delimiters with -D/--delimiters:

# Use #-style (for Python/Shell)
python -m jinjagen template.txt output.txt -D#

# Use /-style (for C/JS)
python -m jinjagen template.c output.c -D/

# Use default Jinja2 delimiters (.)
python -m jinjagen template.html output.html -D.

Custom Delimiter Logic

The delimiter system handles these cases:

1. Conflict Prevention:
   Avoids syntax clashes (e.g., {{ }} in Vue.js or {% %} in Django).
2. Comment Safety:
   Respects language comment styles (e.g., # in Bash won’t break #% blocks).
3. Edge Cases:
   If no extension matches (or for .txt), falls back to standard Jinja2 delimiters.

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Practical Usage 🛠️

Jinjagen shines in generating configs, scripts, and code files. Here are common scenarios:

1. Generate Config Files

Scenario: Create an nginx.conf with dynamic ports and SSL settings.
Template (nginx.conf.j2):

#jinjagen: -D#
server {
  listen #{ port }#;
  server_name #{ domain }#;

  #% if ssl_enabled %#
  ssl_certificate #{ ssl_cert }#;
  ssl_certificate_key #{ ssl_key }#;
  #% endif %#
}

Data (deploy.yml):

port: 443
domain: "example.com"
ssl_enabled: true
ssl_cert: "/etc/ssl/certs/example.crt"
ssl_key: "/etc/ssl/private/example.key"

Command:

python -m jinjagen nginx.conf.j2 nginx.conf -d deploy.yml

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2. Dynamic Script Generation

Scenario: Create a backup script with conditional email alerts.
Template (backup.sh.j2):

#!/bin/bash
#jinjagen: -D#
BACKUP_DIRS=(#% for dir in backup_dirs %# "#{ dir }#" #% endfor %#)

#% if notify %#
echo "Backup done" | mail -s "Backup Log" #{ email }#
#% endif %#

Data (config.json):

{
  "backup_dirs": ["/home", "/etc"],
  "notify": true,
  "email": "admin@example.com"
}

Command:

python -m jinjagen backup.sh.j2 backup.sh -d config.json -D#

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3. CI/CD Pipeline Integration

Scenario: Generate environment-specific .env files during deployment.
Template (.env.j2):

#jinjagen: -D.
DB_HOST=#{ db_host }#
DB_USER=#{ db_user }#
#% if env == "prod" %#
DB_PASSWORD=#{ "vault.get('db_prod_pass')" }#
#% else %#
DB_PASSWORD=devpass
#% endif %#

Command (using environment variables):

python -m jinjagen .env.j2 .env -D# -d <(echo '{"env":"prod","db_host":"10.0.0.1","db_user":"admin"}')

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4. Code Generation

Scenario: Generate a Python class from a template.
Template (model.py.j2):

#jinjagen: -D#
class #{ class_name }#:
    def __init__(self):
        #% for field in fields %#
        self.#{ field }# = None
        #% endfor %#

Data (model.json):

{
  "class_name": "UserModel",
  "fields": ["id", "name", "email"]
}

Command:

python -m jinjagen model.py.j2 UserModel.py -d model.json

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Pro Tips 💡

• Use - for stdin/stdout: Pipe templates/data between tools.

  echo "Hello #{ name }#" | python -m jinjagen -D# - -d <(echo '{"name":"World"}')
  

• Override delimiters when auto-detection fails:

  python -m jinjagen template.sql output.sql -D/  # Force /*% style for SQL
  

• Template directories: Use -t ./templates to enable {% include %}.

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