Systems & CLI · Beginner
cut: Build a Column Extractor
Build a command-line tool that extracts selected fields or columns from delimited text using -f and -d flags, just like Unix cut.
This project recreates the Unix cut utility, which pulls specific columns out of delimited text such as CSV or TSV files. You implement the -f flag to choose one or more fields and the -d flag to set the delimiter, reading from a file or from standard input so it slots into a pipeline. It is worth building because it teaches line-oriented stream processing, field splitting, and the discipline of matching an existing tool's behavior precisely, including how cut handles lines that lack the delimiter. It pairs naturally with a wc clone to build intuition for how the small Unix text tools chain together into data pipelines.
What you build
- Extracts a single field by number with the -f flag
- Extracts multiple fields specified as a list like -f 1,3,5
- Sets a custom delimiter with the -d flag, defaulting to tab
- Reads from a named file or from standard input for piping
- Preserves field order as requested and joins output with the delimiter
- Handles lines that do not contain the delimiter gracefully
- Streams input line by line so it works on large files
What it teaches
- Line-oriented stream processing
- Splitting strings on a configurable delimiter
- Parsing flag arguments including comma-separated lists
- Reading from files and standard input interchangeably
- Matching a reference tool's exact behavior and edge cases
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Take it further
- Support field ranges such as -f 2-4 and open-ended ranges like -f 3-.
- Add a -c flag that cuts by character position instead of by field.
- Add an option to treat repeated delimiters as a single separator.
