Environments in Stata#

Search paths in Stata#

In Stata, we typically do not talk about environments, but the same basic structure applies: Stata searches along a set order for its commands. Some commands are built into the executable (the software that is opened when you click on the Stata icon), but most other internal, and all external commands, are found in a search path. This is typically the ado directory in the Stata installation directory, and one will find replication packages that contain instructions to copy files into that directory. Once we’ve shown how environments work in Stata, this will become a lot simpler!

The sysdir directories#

The default set of directories which can be searched, from a freshly installed Stata, can be queried with the sysdir command, and will look something like this:

sysdir

   STATA:  C:\Program Files\Stata18\
    BASE:  C:\Program Files\Stata18\ado\base\
    SITE:  C:\Program Files\Stata18\ado\site\
    PLUS:  C:\Users\lv39\ado\plus\
PERSONAL:  C:\Users\lv39\ado\personal\
OLDPLACE:  c:\ado\

The adopath search order#

The search paths where Stata looks for commands is queried by adopath, and looks similar, but now has an order assigned to each entry:

adopath

  [1]  (BASE)      "C:\Program Files\Stata18\ado\base/"
  [2]  (SITE)      "C:\Program Files\Stata18\ado\site/"
  [3]              "."
  [4]  (PERSONAL)  "C:\Users\lv39\ado\personal/"
  [5]  (PLUS)      "C:\Users\lv39\ado\plus/"
  [6]  (OLDPLACE)  "c:\ado/"

To look for a command, say reghdfe, Stata will look in the first directory, then the second, and so on, until it finds it. If it does not find it, it will return an error. We can query the location of reghdfe explicitly with which:

which reghdfe

command reghdfe not found as either built-in or ado-file
r(111);

Where are packages installed?#

When we install a package, using one of the various package installation commands (net install, ssc install)[1], only one of the (sysdir) paths is relevant: PLUS. So if we install reghdfe with ssc install reghdfe, it will be installed in the PLUS directory, and we can see that with which:

ssc install reghdfe
which reghdfe

. ssc install reghdfe
checking reghdfe consistency and verifying not already installed...
installing into C:\Users\lv39\ado\plus\...
installation complete.

. which reghdfe
C:\Users\lv39\ado\plus\r\reghdfe.ado
*! version 6.12.3 08aug2023

Important

It is important here to recognize that it is the value of the special sysdir directory PLUS that determines where Stata installs commands, but the separate list of adopath locations where it looks for commands. It is possible to install a command in a location that Stata does not look for commands!

Using environments in Stata#

But the (PLUS) directory can be manipulated, and that creates the opportunity to create an “environment”.

* Set the root directory

global rootdir : pwd

* Define a location where we will hold all packages in THIS project (the "environment")

global adodir "$rootdir/ado"

* make sure it exists, if not create it.

cap mkdir "$adodir"

* Now let's simplify the adopath
* - remove the OLDPLACE and PERSONAL paths
* - NEVER REMOVE THE SYSTEM-WIDE PATHS - bad things will happen!

adopath - OLDPLACE
adopath - PERSONAL

* modify the PLUS path to point to our new location, and move it up in the order

sysdir set PLUS "$adodir"
adopath ++ PLUS

* verify the path

adopath

which should show something like this:

. adopath
  [1]  (PLUS)      "C:\Users\lv39\Documents/PROJECT123/ado/"
  [2]  (BASE)      "C:\Program Files\Stata18\ado\base/"
  [3]  (SITE)      "C:\Program Files\Stata18\ado\site/"
  [4]              "."

Let’s verify again where the reghdfe package is:

which reghdfe

. which reghdfe
command reghdfe not found as either built-in or ado-file
r(111);

So it is no longer found. Why? Because we have removed the previous location (the old PLUS path) from the search sequence. It’s as if it didn’t exist.

Installing packages when an environment is active#

When we now install reghdfe again:

. ssc install reghdfe
checking reghdfe consistency and verifying not already installed...
installing into C:\Users\lv39\Documents\PROJECT123\ado\plus\...
installation complete.

. which reghdfe
C:\Users\lv39\Documents\PROJECT123\ado\plus\r\reghdfe.ado
*! version 6.12.3 08aug2023

We now see it in the project-specific directory, which we can distribute with the whole project (more on that later).

Installing precise versions of packages#

Let’s imagine we need an older version of reghdfe. In general, it is not possible in Stata to install an older version of a package in a straightforward fashion. You may have success with the Wayback Machine archive of SSC, which in some cases goes back to 2000, by carefully reconstructing the necessary files.

Here, we will leverage the SSC Snapshot maintained by Lars Vilhuber on Github (labordynamicsinstitute/ssc-mirror), which has been capturing snapshots of SSC since late 2021 (details are for a different tutorial):

* define the date
global sscdate "2021-12-21"
net install reghdfe, from(https://raw.githubusercontent.com/labordynamicsinstitute/ssc-mirror/${sscdate}/fmwww.bc.edu/repec/bocode/r)

which gives us

. net install reghdfe, from(https://raw.githubusercontent.com/labordynamicsinsti
> tute/ssc-mirror/${sscdate}/fmwww.bc.edu/repec/bocode/r)
checking reghdfe consistency and verifying not already installed...
installing into C:\Users\lv39\Documents/ado\...
installation complete.

. which reghdfe
C:\Users\lv39\Documents/ado\r\reghdfe.ado
*! version 5.7.3 13nov2019

So we now have TWO different version of reghdfe installed:

  • Version 5.7.3 from Nov 2019 is installed at C:\Users\lv39\Documents/ado\r\reghdfe.ado

  • Version 6.12.3 from Aug 2023 is installed at C:\Users\lv39\ado\plus\r\reghdfe.ado

Stata can get confused about how to write paths…

Stata on Windows can understand two types of path syntax: the “Windows” syntax, with backslashes \, and the “Unix” syntax, with forward slashes ‘/’. It will usually report paths in the “Windows” syntax, but these will not work, if coded as such, on non-Windows platforms, which do not understand the backslash as a path separator. We have used platform-agnostic paths above, using forward slashes. This then generates the “weird” mixed notation:

C:\Users\lv39\Documents/ado\r\reghdfe.ado

Other software (e.g, R), will consistently use the forward slash, even on Windows, when paths are coded internally.

Only the former is used by the “environment” we just configured! Which is a good thing, since there are a few functional differences between these two packages. But for the life of this project, that functionality can now be relied upon - as long as we take care to use the same “environment” for all code run within this project. This can be achieved by using the main.do defined in one of the previous sections:

* main.do
* This is a simple example of a main file in Stata
* It runs all the other files in the correct order

* Set the root directory

global rootdir : pwd

* Define a location where we will hold all packages in THIS project (the "environment")

global adodir "$rootdir/ado"

* Enable project environment

cap mkdir "$adodir"
adopath - OLDPLACE
adopath - PERSONAL
sysdir set PLUS "$adodir"
adopath ++ PLUS
adopath

* Run the data preparation file
do $rootdir/01_data_prep.do

// etc. etc.

Warning

While we used interactive commands to install the various packages here, that was only for illustrative purposes. Always script the installation of packages in a setup.do file. We will address how and when to run that file in the next section.