'`
1) If people are using bash with `set -u` (enable unset variable
checking), then they will get an error if they run `pyenv` in the
CLI under the current setup. To avoid any errors when no positional
arguments, we use ${1:-} instead of $1.
2) We find that the script looks better when using:
```bash
echo \
'pyenv() {
local command=${1:-}'
```
As opposed to:
```
echo 'pyenv() {
local command=${1:-}'
```
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