> For the complete documentation index, see [llms.txt](https://openai.gitbook.io/code-cheatsheets/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://openai.gitbook.io/code-cheatsheets/all/bash/io.md).

# IO in Bash

Each open file gets assigned a file descriptor. [\[2\]](https://www.tldp.org/LDP/abs/html/io-redirection.html#FTN.AEN17894) The file descriptors for `stdin`, `stdout`, and `stderr` are 0, 1, and 2, respectively.

## Basics

| Command                           | do                                               |                                |
| --------------------------------- | ------------------------------------------------ | ------------------------------ |
| \[cmd] > \[filename]              | Redirects stdout to file creating or overwriting | echo "hi" > test.txt           |
| \[cmd] >> \[filename]             | Appends stdout to file if it exists, or creates  | echo "Thank you" >> test.txt   |
| 1>\[filename]                     | redirect stdout to file                          | echo "Dream better" 1>$LOGFILE |
| 2>\[filename]                     | redirect stdeer                                  | bad\_command1 2>$ERRORFILE     |
| &>\[filename]  ORR  >&\[filename] | redirect both stdout and stderr                  |                                |
| 0< FILENAME                       | accept input from a file                         |                                |

### Pipes

General purpose comman chaining

cat \*.txt | sort | uniq > test.txt

## Advanced Stupid Stuff

| Cmd             | do                          | Ex           |
| --------------- | --------------------------- | ------------ |
| : > \[filename] | make file empty             | : > test.txt |
| 2>&1            | Redirects stderr to stdout. |              |