---
title: env_append
description: Append an item to a list-like environment variable.
---

# `env_append`

`env_append` returns a dependency that adds one item to the end of an environment variable. Items are joined with the host path-list separator, making the function suitable for `PATH` and similar variables.

## Arguments

| Argument | Required | Description |
| --- | --- | --- |
| `key` | Yes | Environment variable name to change. |
| `value` | Yes | String item to append. |
| `unique` | No | Keep the existing value when an equivalent item is already present. Defaults to `False`. |

Uniqueness uses exact string comparison on Linux and macOS. On Windows, `PATH` entries are compared case-insensitively; other variables use exact comparison.

## Examples

### Append one search path

```python
load("@os@1", "env_append", "run")

run(
    ("project-linter", "check"),
    deps=[env_append("PATH", "tools/bin")],
)
```

### Avoid duplicate entries

```python
load("@os@1", "env_append", "run")

tool_paths = (
    env_append("PATH", "tools/bin", unique=True) +
    env_append("PATH", "vendor/bin", unique=True)
)

run(("project-linter", "check"), deps=[tool_paths])
```

<!--
Sitemap

URL: https://withxx.dev/index.md
Title: xx
Description: Practical, reproducible builds without build-system ceremony

URL: https://withxx.dev/examples/commands.md
Title: Command Examples
Description: General command, environment, and entrypoint patterns.

URL: https://withxx.dev/examples/go.md
Title: Go Examples
Description: Common Go build patterns with managed SDKs.

URL: https://withxx.dev/examples/nodejs.md
Title: Node.js Examples
Description: Common Node.js task patterns with a managed distribution.

URL: https://withxx.dev/examples/zig.md
Title: Zig Examples
Description: Direct Zig commands and Go CGO builds with a managed Zig distribution.

URL: https://withxx.dev/load.md
Title: Loading Files
Description: Split xx configuration into local Starlark modules.

URL: https://withxx.dev/packages/go/go.md
Title: go
Description: Activate a managed Go SDK for dependent tasks.

URL: https://withxx.dev/packages/go/go_binary.md
Title: go_binary
Description: Build a Go command with a managed SDK.

URL: https://withxx.dev/packages/go/go_install.md
Title: go_install
Description: Install a versioned Go command for dependent tasks.

URL: https://withxx.dev/packages/go/go_run.md
Title: go_run
Description: Run a versioned Go command with a managed SDK.

URL: https://withxx.dev/packages/go/go_test.md
Title: go_test
Description: Test Go packages with a managed SDK.

URL: https://withxx.dev/packages/nodejs/nodejs.md
Title: nodejs
Description: Activate managed Node.js for dependent tasks.

URL: https://withxx.dev/packages/nodejs/npm_install.md
Title: npm_install
Description: Install project dependencies with managed npm.

URL: https://withxx.dev/packages/nodejs/npm_run.md
Title: npm_run
Description: Run a project package script with managed npm.

URL: https://withxx.dev/packages/nodejs/npx_run.md
Title: npx_run
Description: Run a versioned npm package command with managed npx.

URL: https://withxx.dev/packages/os/env_append.md
Title: env_append
Description: Append an item to a list-like environment variable.

URL: https://withxx.dev/packages/os/env_get.md
Title: env_get
Description: Read a value from a task environment while evaluating Starlark.

URL: https://withxx.dev/packages/os/env_prepend.md
Title: env_prepend
Description: Prepend an item to a list-like environment variable.

URL: https://withxx.dev/packages/os/env_set.md
Title: env_set
Description: Set an environment variable for dependent tasks.

URL: https://withxx.dev/packages/os/env_unset.md
Title: env_unset
Description: Remove an environment variable from dependent tasks.

URL: https://withxx.dev/packages/os/run.md
Title: run
Description: Run a command from the project root.

URL: https://withxx.dev/packages/zig/zig.md
Title: zig
Description: Activate managed Zig for dependent tasks.

URL: https://withxx.dev/packages/zig/zig_cc.md
Title: zig_cc
Description: Configure managed Zig as a C and C++ compiler.

URL: https://withxx.dev/packages.md
Title: Built-in Packages
Description: Versioned toolchains, commands, and task environment helpers provided by xx.
-->