First, let’s cover some setup hooks that are part of Nixpkgs default `stdenv`. This means that they are run for every package built using `stdenv.mkDerivation`, even with custom builders. Some of these are platform specific, so they may run on Linux but not Darwin or vice-versa.

### `move-docs.sh` {#move-docs.sh}

This setup hook moves any installed documentation to the `/share` subdirectory directory. This includes the man, doc and info directories. This is needed for legacy programs that do not know how to use the `share` subdirectory.

### `compress-man-pages.sh` {#compress-man-pages.sh}

This setup hook compresses any man pages that have been installed. The compression is done using the gzip program. This helps to reduce the installed size of packages.

### `strip.sh` {#strip.sh}

This runs the strip command on installed binaries and libraries. This removes unnecessary information like debug symbols when they are not needed. This also helps to reduce the installed size of packages.

### `patch-shebangs.sh` {#patch-shebangs.sh}

This setup hook patches installed scripts to add Nix store paths to their shebang interpreter as found in the build environment. The [shebang](https://en.wikipedia.org/wiki/Shebang_(Unix)) line tells a Unix-like operating system which interpreter to use to execute the script's contents.

::: {.note}
The [generic builder][generic-builder] populates `PATH` from inputs of the derivation.
:::


#### Invocation {#patch-shebangs.sh-invocation}

Multiple paths can be specified.

```
patchShebangs [--build | --host] PATH...
```

##### Flags {#patch-shebangs.sh-invocation-flags}

`--build`
: Look up commands available at build time

`--host`
: Look up commands available at run time

##### Examples {#patch-shebangs.sh-invocation-examples}

```sh
patchShebangs --host /nix/store/<hash>-hello-1.0/bin
```

```sh
patchShebangs --build configure
```

`#!/bin/sh` will be rewritten to `#!/nix/store/<hash>-some-bash/bin/sh`.

`#!/usr/bin/env` gets special treatment: `#!/usr/bin/env python` is rewritten to `/nix/store/<hash>/bin/python`.

Interpreter paths that point to a valid Nix store location are not changed.

::: {.note}
A script file must be marked as executable, otherwise it will not be
considered.
:::

This mechanism ensures that the interpreter for a given script is always found and is exactly the one specified by the build.

It can be disabled by setting [`dontPatchShebangs`](#var-stdenv-dontPatchShebangs):

```nix
stdenv.mkDerivation {
  # ...
  dontPatchShebangs = true;
  # ...
}
```

The file [`patch-shebangs.sh`][patch-shebangs.sh] defines the [`patchShebangs`][patchShebangs] function. It is used to implement [`patchShebangsAuto`][patchShebangsAuto], the [setup hook](#ssec-setup-hooks) that is registered to run during the [fixup phase](#ssec-fixup-phase) by default.

If you need to run `patchShebangs` at build time, it must be called explicitly within [one of the build phases](#sec-stdenv-phases).


### `audit-tmpdir.sh` {#audit-tmpdir.sh}

This verifies that no references are left from the install binaries to the directory used to build those binaries. This ensures that the binaries do not need things outside the Nix store. This is currently supported in Linux only.

### `multiple-outputs.sh` {#multiple-outputs.sh}

This setup hook adds configure flags that tell packages to install files into any one of the proper outputs listed in `outputs`. This behavior can be turned off by setting `setOutputFlags` to false in the derivation environment. See [](#chap-multiple-output) for more information.

### `move-sbin.sh` {#move-sbin.sh}

This setup hook moves any binaries installed in the `sbin/` subdirectory into `bin/`. In addition, a link is provided from `sbin/` to `bin/` for compatibility.

### `move-lib64.sh` {#move-lib64.sh}

This setup hook moves any libraries installed in the `lib64/` subdirectory into `lib/`. In addition, a link is provided from `lib64/` to `lib/` for compatibility.

### `move-systemd-user-units.sh` {#move-systemd-user-units.sh}