Add Set Environment Variables When Creating Session as a tmux til

tmux/set-environment-variables-when-creating-session.md

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+# Set Environment Variables When Creating Session
+
+In [Set Session-Specific Environment
+Variables](set-session-specific-environment-variables.md), I showed how env
+vars that are scoped to a tmux session can be set in an existing session.
+
+It is also possible to set any number of environment variables when creating a
+session. This is particularly handy if you are scripting the setup of various
+tmux environments.
+
+A base command to start a tmux session might look like this:
+
+```bash
+$ tmux new -s my-project
+```
+
+To set environment variables on that session, use one or more `-e` flags
+followed by the name and value.
+
+```bash
+$ tmux new -s my-project -e EDITOR=code -e PG_VERSION=13.4
+```
+
+See `man tmux` for more details.