# Introduction

**Miller is a command-line tool for querying, shaping, and reformatting data files in various formats, including CSV, TSV, JSON, and JSON Lines.**

**The big picture:** Even well into the 21st century, our world is full of text-formatted data such as CSV. Google _CSV memes_, for example. We need tooling to _thrive in this world_, nimbly manipulating data which is in CSVs. And we need tooling to _move beyond CSV_, to be able to pull data out and into other storage and processing systems. Miller is designed for both of these goals.

In several senses, Miller is more than one tool:

**Format conversion:** You can convert CSV files to JSON, or vice versa, or
pretty-print your data horizontally or vertically to make it easier to read.

**Data manipulation:** With a few keystrokes, you can remove columns you don't care about -- or make new ones.

**Pre-processing/post-processing vs standalone use:** You can use Miller to clean data files and put them into standard formats, perhaps in preparation for loading them into a database or a hands-off data-processing pipeline. Or you can use it post-process and summarize database-query output. As well, you can use Miller to explore and analyze your data interactively.

**Compact verbs vs programming language:** For low-keystroking, you can do things like

GENMD-SHOW-COMMAND
mlr --csv sort -f name input.csv
GENMD-EOF

GENMD-SHOW-COMMAND
mlr --json head -n 1 myfile.json
GENMD-EOF

The `sort`, `head`, etc., are called *verbs*. They're analogs of familiar command-line tools like `sort`, `head`, and so on -- but they're aware of name-indexed, multi-line file formats like CSV, TSV, and JSON. In addition, though, using Miller's `put` verb, you can use programming-language statements for expressions like

GENMD-SHOW-COMMAND
mlr --csv put '$rate = $units / $seconds' input.csv
GENMD-EOF

which allow you to express your own logic succinctly.

**Multiple domains:** People use Miller for data analysis, data science, software engineering, devops/system-administration, journalism, scientific research, and more.

In the following, you can see how CSV, TSV, tabular, JSON, and other **file formats** share a common theme which is **lists of key-value-pairs**. Miller embraces this common theme.

![coverart/cover-combined.png](coverart/cover-combined.png)
