When And Why To Use Interactive Vs Non-Interactive Shells

What are Interactive and Non-Interactive Shells?

An interactive shell allows a user to directly execute commands and view output in real-time. Common examples include bash, zsh, and other Linux/UNIX shells accessed via a terminal or command line interface. Users can explore data, prototype code, and convenient everyday tasks through immediate feedback.

A non-interactive shell executes a pre-determined set of commands without ongoing human interaction. Common examples include shell scripts, cron jobs, and other types of batch execution. These are used to automate repetitive tasks, schedule background jobs, and run complex multi-step procedures.

Key Differences

Interactive shells provide live user I/O, non-interactive shells run automated commands
Interactive shells offer flexibility for exploration, non-interactive shells provide consistency for automation
Interactive shells allow trial-and-error discovery, non-interactive shells execute defined instructions

Examples of Common Interactive Shells

Bash – Default shell in most Linux distributions, powerful and flexible
Zsh – Advanced interactive shell with additional features and customization
Fish – User-friendly shell aimed at simplicity and usability
Powershell – Default interactive shell in Windows, for access to system functions

Examples of Common Non-Interactive Shells

Bash scripts – Files with .sh extension containing bash commands to be executed
Cron jobs – Background tasks scheduled by a cron daemon to run scripts or programs
Docker containers – Isolated environments based on images defining non-interactive behavior
Makefiles – Declarative build automation using target rules for compilation and tasks

Advantages of Interactive Shells

Interactive shells provide important benefits centered around direct human involvement and real-time usage:

Live Feedback and Ability to Try Commands

The interactive loop allows trying out commands and instantly seeing results, errors, output, etc. This supports an exploratory style workflow with hands-on discovery of available tools and components. The tight feedback loop enables organic growth of knowledge through experimentation.

Exploratory Data Analysis and Prototyping

Data scientists and developers often leverage interactive shells for querying data in ad hoc ways, testing statistical models, creating quick scripts, debugging in real time, and similar activities requiring evaluation and adjustment. Interactive shells facilitate these pretty fluid tasks.

Convenient for Everyday Tasks

For daily administrative work and common tasks, an interactive shell avoids the overhead of writing separate scripts – especially for one-off or disorganized work. Productivity thrives in interactive shells due to their responsiveness and human touch.

Advantages of Non-Interactive Shells

Non-interactive shells excel when it comes to predefined automation, scheduling, and uninterrupted batch processing:

Automating Repetitive Tasks

Any task needing to be run repetitively can be automated as a shell script or cron job. This eliminates human redundancy and manual overhead for recurring work that follows a fixed pattern.

Scheduling Jobs and Tasks

Background cron jobs allow scheduling shell scripts, programs, and other tasks to trigger at fixed intervals or designated times. Scheduling removes the need for manual triggering or memory of when to execute tasks.

Executing Complex Multi-Step Procedures

Lengthy workflows requiring orchestration across tools, phases, conditional logic, error handling, and callbacks can be codified into a non-interactive script for reliability and control.

Determining Which Shell Type to Use

Certain key considerations should guide whether an interactive or non-interactive shell makes more sense:

Consider Need for Human Interaction vs Automation

If ad hoc analysis or frequent changes are likely required, an interactive shell enables easier tweaks over rewriting scripts. But defined or productionized procedures often benefit more from non-interactive automation.

Balance Flexibility and Repeatability

Non-interactive approaches sacrifice flexibility but enforce repeatability, while interactive shells provide freedom at the cost of discipline. Balance is needed across a workflow lifecycle evolving from experimentation to hardened execution.

Security Tradeoffs of Interactivity vs Non-interactivity

Allowing human interaction creates more surface area for errors and malicious actions than with predefined scripts. But auditing automation also has unique challenges regarding permissions, access controls and more.

Example Code Snippets

Some basic examples contrast styles and usage:

Starting an interactive bash session

  
  $ bash 
  [user@host ~]$ ls
  [user@host ~]$ cd /home
  [user@host home]$ pwd
  /home

Writing a simple shell script

  
  #!/bin/bash
  echo "Running script to backup files..." 
  rsync -avh /source/dir /backups/destination  
  echo "Backup completed successfully"

Setting up a cron job

  
  # Run at 10pm (22:00) every day
  00 22 * * * /path/to/script.sh

Key Takeways and Recommendations

To utilize both interactive and non-interactive shells most effectively:

Use interactive shells for experimentation, analysis, and development workflows
Use non-interactive shells for hardened automation, production jobs, scheduling
Start with interactive exploration then optimize repeatable procedures
Balance flexibility demands with stability needs across lifecycle
Audit scripts and cron jobs for security just like interactive access

The two approaches can scale from individuals to teams when roles, responsibilities and integration points are clearly defined.