bug-detective

Start by collecting the full error message, stack trace, and reproduction steps. Classify the error type (TypeError, KeyError, IndexError, etc.), then use binary search, logging, or pdb breakpoints to locate the source before forming and verifying a hypothesis about the cause.

Run the script with bash -x to trace each command, and add set -euo pipefail at the top so errors, undefined variables, and pipe failures stop execution immediately. ShellCheck can statically detect common mistakes like unquoted variables before runtime.

Frequent patterns include mutable default arguments, modifying a list while iterating over it, closure variable binding in loops, using is for value comparison, and accessing None object attributes. Each has a standard fix such as using None defaults or list comprehensions.

Piping into a while loop creates a subshell, so variable changes do not persist outside it. Replace the pipe with input redirection or process substitution, for example while read line; do ... done < file.txt, to keep the loop in the current shell.

Use git bisect when a bug appeared at an unknown point in history and you have a known-good commit. It binary-searches commits between good and bad states to identify the exact commit that introduced the regression.