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Many scientists write code as part of their research.  Just as experiments are logged in laboratory notebooks, it is important to document the code you use for analysis.  However, a few key problems can arise when iteratively developing code that make it difficult to document and track which code version  was used to create each result. First, you often need to experiment with new ideas, such as adding new features to a script or increasing the speed of a slow step, but you do not want to risk breaking the currently working code.  The simplest solution is to make a copy the script before making new edits.  However, this can quickly become a problem because it clutters your filesystem with uniformative filenames, e.g. \verb|analysis.sh|, \verb|analysis_02.sh|, \verb|analysis_03.sh|, etc.