Shell Environment Configuration

To identify the currently active command interpreter, query the SHELL environment varible:

echo "$SHELL"

A comprehensive list of interpreters installed on the system can be retrieved via:

cat /etc/shells
# Alternatively: chsh --list

Modifying the default login shell requires appropriate user permissions using the chsh utility:

chsh -s /bin/zsh  # Set Zsh as default
chsh -s /bin/bash # Set Bash as default

Background and Foreground Job Management

Executing long-running tasks in the terminal often requires shifting them between active and suspended states.

• Pause foreground process: Press Ctrl + Z to suspend the currently running command and return control to the prompt.
• List suspended/runing jobs: Execute jobs to view all background tasks associated with the current terminal session.
• Resume in background: Use bg to continue a paused job without occupying the terminal interface.
• Return to foreground: Invoke fg to bring a background task back to active interaction.
• Detach from terminal: Prefix commands with nohup to prevent termination when the session ends:

  nohup ./data_processing.sh > execution.log 2>&1 &
  

• Filter processes by working directory: Locate all active processes originating from a specific path:

  ps aux | grep "$(pwd)"
  

Storage Monitoring

Inspect available and utilized filesystem volumes with human-readable formatting:

df -h

Network Port Analysis

Identify open TCP listening sockets on the local machine. The following pipeline isolates ports containing a specific numeric sequence:

netstat -tlnp | grep ":8080"

Standard I/O Stream Redirection

Understanding file descriptors is critical for managing command output:

• 0: Standard Input (stdin)
• 1: Standard Output (stdout)
• 2: Standard Error (stderr)

Key redirection operators:

• command 2>&1: Merges error output with standard output, directing both to the same stream or destination.
• command 2> error_only.txt: Routes error messages exclusively to error_only.txt, leaving standard output visible on the terminal.
• command 2>&1 > combined.log: Redirects standard error to the terminal while sending standard output to a file (order matters in bash).
• command 2> '&1': Treats &1 as a literal filename rather than a stream reference, creating a file named exactly &1.

Text Processing Utilities

Pattern Matching with Extended Regex Filter lines containing multiple distinct patterns from a target file:

grep -E "timeout|connection_refused|fatal" system.log

Data Deduplication Remove duplicate entries from a dataset by combining sorting and filtering:

sort inventory_list.csv | uniq > deduplicated_results.csv

Alternatively, achieve identical results using the built-in unique flag for streamlined execution:

sort -u inventory_list.csv > deduplicated_results.csv