> For the complete documentation index, see [llms.txt](https://julienbeaulieu.gitbook.io/wiki/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://julienbeaulieu.gitbook.io/wiki/sciences/programming/command-line.md).

# Command Line

#### Select columns from a file

```
cut -f 2-5,8 -d , values.csv
```

"select columns 2 through 5 and columns 8, using comma as the separator". `cut` uses `-f` (meaning "fields") to specify columns and `-d` (meaning "delimiter") to specify the separator.

#### History

`history` will print a list of commands you have run recently. Each one is preceded by a serial number to make it easy to re-run particular commands: just type `!55` to re-run the 55th command in your history (if you have that many). You can also re-run a command by typing an exclamation mark followed by the command's name, such as `!head` or `!cut`, which will re-run the most recent use of that command.

#### Grep

**How can I select lines containing specific values?**

`head` and `tail` select rows, `cut` selects columns, and `grep` selects lines according to what they contain. In its simplest form, `grep` takes a piece of text followed by one or more filenames and prints all of the lines in those files that contain that text. For example, `grep bicuspid seasonal/winter.csv` prints lines from `winter.csv` that contain "bicuspid".

`grep` can search for patterns as well; we will explore those in the next course. What's more important right now is some of `grep`'s more common flags:

* `-c`: print a count of matching lines rather than the lines themselves
* `-h`: do *not* print the names of files when searching multiple files
* `-i`: ignore case (e.g., treat "Regression" and "regression" as matches)
* `-l`: print the names of files that contain matches, not the matches
* `-n`: print line numbers for matching lines
* `-v`: invert the match, i.e., only show lines that *don't* match