From b68ec4e9c108e0378787a289b78d20a531485dca Mon Sep 17 00:00:00 2001
From: Mike Peachey <mike.peachey@bjss.com>
Date: Fri, 24 Apr 2026 16:34:18 +0100
Subject: [PATCH] Support tfenv use - to switch to previous version

Similar to cd -, tfenv use - now switches back to the previously
active default version. The previous version is saved to
\$TFENV_CONFIG_DIR/version.prev each time tfenv use writes a new
default. Running tfenv use - again toggles between the two versions.

If no previous version exists, the command errors with a clear
message.

Also adds version.prev cleanup to the cleanup() helper in
lib/helpers.sh to prevent test pollution.

Fixes #378
---
 lib/helpers.sh        |  2 ++
 libexec/tfenv-use     | 24 ++++++++++++++++++++++
 test/test_use_dash.sh | 47 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 73 insertions(+)
 create mode 100755 test/test_use_dash.sh

diff --git a/lib/helpers.sh b/lib/helpers.sh
index 696f6b8c..ab38f4b0 100755
--- a/lib/helpers.sh
+++ b/lib/helpers.sh
@@ -154,6 +154,8 @@ function cleanup() {
   
   log 'debug' "Deleting ${TFENV_CONFIG_DIR}/version";
   rm -rf "${TFENV_CONFIG_DIR}/version";
+  log 'debug' "Deleting ${TFENV_CONFIG_DIR}/version.prev";
+  rm -rf "${TFENV_CONFIG_DIR}/version.prev";
   log 'debug' "Deleting ${TFENV_CONFIG_DIR}/versions";
   rm -rf "${TFENV_CONFIG_DIR}/versions";
   log 'debug' "Deleting ${pwd}/.terraform-version";
diff --git a/libexec/tfenv-use b/libexec/tfenv-use
index 24de91fa..4a932f6c 100755
--- a/libexec/tfenv-use
+++ b/libexec/tfenv-use
@@ -72,6 +72,18 @@ declare version_source_suffix="";
 declare requested="${requested_arg}";
 declare loaded_version_file="$(tfenv-version-file)";
 
+# Handle 'tfenv use -' to switch to previous version
+if [ "${requested_arg}" == '-' ]; then
+  declare prev_file="${TFENV_CONFIG_DIR}/version.prev";
+  [ -f "${prev_file}" ] \
+    || log 'error' 'No previous version to switch to. Use tfenv use <version> first.';
+  requested_arg="$(cat "${prev_file}" | tr -d '\r')";
+  [ -n "${requested_arg}" ] \
+    || log 'error' 'Previous version file is empty.';
+  requested="${requested_arg}";
+  log 'info' "Switching to previous version: ${requested_arg}";
+fi;
+
 if [ -z "${requested_arg}" -a -z "${TFENV_TERRAFORM_VERSION:-""}" ]; then
   version_source_suffix=" (set by ${loaded_version_file})";
 
@@ -154,6 +166,18 @@ log 'debug' "target_path is ${TFENV_CONFIG_DIR}/versions/${installed_version}";
 
 log 'info' "Switching default version to v${installed_version}";
 version_file="${TFENV_CONFIG_DIR}/version";
+
+# Save current version as previous before overwriting
+if [ -f "${version_file}" ]; then
+  declare current_version;
+  current_version="$(cat "${version_file}" | tr -d '\r')" || true;
+  if [ -n "${current_version}" ] && [ "${current_version}" != "${installed_version}" ]; then
+    log 'debug' "Saving previous version '${current_version}' to ${version_file}.prev";
+    echo "${current_version}" > "${version_file}.prev" \
+      || log 'warn' "Failed to save previous version to ${version_file}.prev";
+  fi;
+fi;
+
 log 'debug' "Writing \"${installed_version}\" to \"${version_file}\"";
 echo "${installed_version}" > "${version_file}" \
   || log 'error' "Switch to v${installed_version} failed";
diff --git a/test/test_use_dash.sh b/test/test_use_dash.sh
new file mode 100755
index 00000000..b0575614
--- /dev/null
+++ b/test/test_use_dash.sh
@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+
+# Source common test setup
+source "$(dirname "${0}")/test_common.sh";
+
+#####################
+# Begin Script Body #
+#####################
+
+declare -a errors=();
+
+log 'info' '### Test Suite: tfenv use -';
+cleanup || log 'error' 'Cleanup failed?!';
+
+log 'info' '## Test: tfenv use - switches to previous version';
+(
+  tfenv install 0.12.1 || exit 1;
+  tfenv install 0.12.2 || exit 1;
+
+  tfenv use 0.12.1 || exit 1;
+  check_active_version 0.12.1 || exit 1;
+
+  tfenv use 0.12.2 || exit 1;
+  check_active_version 0.12.2 || exit 1;
+
+  # Switch back to previous
+  tfenv use - || exit 1;
+  check_active_version 0.12.1 || exit 1;
+
+  # Switch back again
+  tfenv use - || exit 1;
+  check_active_version 0.12.2 || exit 1;
+) && log 'info' '## Test passed: tfenv use - switches to previous version' \
+  || error_and_proceed 'tfenv use - switches to previous version';
+
+log 'info' '## Test: tfenv use - fails with no previous version';
+cleanup || log 'error' 'Cleanup failed?!';
+(
+  tfenv install 0.12.1 || exit 1;
+  # No previous version set yet — use - should fail
+  tfenv use - 2>/dev/null && exit 1 || exit 0;
+) && log 'info' '## Test passed: tfenv use - fails with no previous version' \
+  || error_and_proceed 'tfenv use - fails with no previous version';
+
+finish_tests 'use-dash';
+exit 0;
+# vim: set ts=2 sw=2 et: