diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 1a0010c..7aae71c 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -90,6 +90,39 @@ jobs:
         env:
           GH_TOKEN: ${{ secrets.GH_PAT }}
 
+  tests-file:
+    name: test updates w/ file
+    runs-on: "ubuntu-latest"
+    if: github.event.pull_request.title != 'relock w/ conda-lock'
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: make a copy of lock file
+        shell: bash -leo pipefail {0}
+        run: |
+          cp conda-lock.yml old-conda-lock.yml
+
+      - name: relock
+        id: relock
+        uses: ./
+        with:
+          environment-file: test-env.yml
+          lock-file: conda-lock.yml
+          ignored-packages: ''
+          relock-all-packages: false
+          github-token: ${{ secrets.GH_PAT }}
+          action: file
+
+      - name: did it relock?
+        if: steps.relock.outputs.relocked != 'true'
+        run: exit 1
+
+      - name: test that lock file is different
+        if: steps.relock.outputs.relocked == 'true'
+        shell: bash
+        run: |
+          diff conda-lock.yml old-conda-lock.yml && exit 0 || exit 1
+
   tests-no-lock:
     name: test no update
     runs-on: "ubuntu-latest"
diff --git a/README.md b/README.md
index 7af0c9f..f54d04d 100644
--- a/README.md
+++ b/README.md
@@ -26,32 +26,40 @@ jobs:
           github-token: ${{ secrets.GITHUB_PAT }}
 
           # files to relock w/ conda-lock
-          # environment-file: environment.yml  # default
-          # lock-file: conda-lock.yml  # default
+          environment-file: environment.yml  # default
+          lock-file: conda-lock.yml  # default
 
           # optional list of packages whose changes are ignore when relocking
+          ignored-packages: ""  # default
           # ignored-packages: "numpy,scipy"
 
           # use only these packages to determine if a relock is needed
+          include-only-packages: ""  # default
           # include-only-packages: "numpy,scipy"
 
           # whether to relock on an update to any package in the environment,
           # not just those in the environment file
-          # relock-all-packages: false  # default
+          relock-all-packages: false  # default
 
+          # action to take if we relock
+          # one of 'pr' (make a PR) or 'file' (leave new lock file in CWD)
+          action: 'pr'  # default
+
+          # these options apply only if we are making PRs
           # automerge the PR - you need to have GitHub automerge enabled
-          # automerge: false  # default
+          automerge: false  # default
 
           # use this setting to fix issues with the base branch not
           # being inferred correctly
           # See https://github.com/peter-evans/create-pull-request/blob/main/docs/concepts-guidelines.md#events-which-checkout-a-commit
+          base-branch: ""  # default
           # base-branch: blah
 
           # the head branch for PRs
-          # head-branch: relock-conda  # default
+          head-branch: relock-conda  # default
 
           # whether to skip relocking if a PR already exists
-          # skip-if-pr-exists: false  # default
+          skip-if-pr-exists: false  # default
 ```
 
 See the [action.yml](action.yml) for details on possible inputs and options.
diff --git a/action.yml b/action.yml
index d3187a7..fd535c8 100644
--- a/action.yml
+++ b/action.yml
@@ -31,6 +31,12 @@ inputs:
   github-token:
     description: 'GitHub personal access token to use for making PRs'
     required: true
+  action:
+    description: >
+      the action to take if the lock file is updated: `pr` will make a PR; `file` will leave the updated lock file
+      in the current working directory
+    required: true
+    default: 'pr'
   automerge:
     description: 'whether to automatically merge the PR'
     required: true
@@ -63,6 +69,7 @@ runs:
     # https://stackoverflow.com/a/73828715/1745538
     - name: skip if PR already exists
       id: check
+      if: inputs.action == 'pr'
       shell: bash -leo pipefail {0}
       run: |
         prs=$(gh pr list \
@@ -79,6 +86,13 @@ runs:
         GH_TOKEN: ${{ inputs.github-token }}
         SKIP_IF_PR_EXISTS: ${{ inputs.skip-if-pr-exists }}
 
+    - name: do not skip for non-PR actions
+      id: check
+      if: inputs.action != 'pr'
+      shell: bash -leo pipefail {0}
+      run: |
+        echo "skip=false" >> "$GITHUB_OUTPUT"
+
     - name: setup conda-lock
       if: ${{ steps.check.outputs.skip != 'true' }}
       uses: mamba-org/setup-micromamba@f8b8a1e23a26f60a44c853292711bacfd3eac822 # v1
@@ -117,7 +131,10 @@ runs:
 
     - name: open PR
       id: pr
-      if: steps.check.outputs.skip != 'true' && steps.relock.outputs.env_relocked == 'true'
+      if: >-
+        steps.check.outputs.skip != 'true'
+        && steps.relock.outputs.env_relocked == 'true'
+        && inputs.action == 'pr'
       uses: peter-evans/create-pull-request@c5a7806660adbe173f04e3e038b0ccdcd758773c # v6
       with:
         commit-message: relock w/ conda-lock
@@ -133,7 +150,12 @@ runs:
         base: ${{ inputs.base-branch }}
 
     - name: automerge
-      if: steps.check.outputs.skip != 'true' && inputs.automerge == 'true' && steps.relock.outputs.env_relocked == 'true' && steps.pr.outputs.pull-request-number != ''
+      if: >-
+        steps.check.outputs.skip != 'true'
+        && inputs.automerge == 'true'
+        && steps.relock.outputs.env_relocked == 'true'
+        && steps.pr.outputs.pull-request-number != ''
+        && inputs.action == 'pr'
       shell: bash -leo pipefail {0}
       run: gh pr merge --merge --auto "${{ steps.pr.outputs.pull-request-number }}"
       env:
@@ -144,10 +166,27 @@ runs:
       if: always()
       shell: bash -leo pipefail {0}
       run: |
+        # if we skipped, we did not relock
         if [[ '${{ steps.check.outputs.skip }}' == 'true' ]]; then
           echo "relocked=false" >> "$GITHUB_OUTPUT"
-        elif [[ '${{ steps.relock.outputs.env_relocked }}' == 'true' && '${{ steps.pr.outputs.pull-request-number }}' != '' ]]; then
+          exit 0
+        fi
+
+        if [[ '${{ steps.relock.outputs.env_relocked }}' == 'true' ]]; then
+          # for a PR, we need to know if it was opened
+          if [[ '${{ inputs.action }}' == 'pr' ]]; then
+            if [[ '${{ steps.pr.outputs.pull-request-number }}' != '' ]]; then
+              echo "relocked=true" >> "$GITHUB_OUTPUT"
+            else
+              echo "relocked=false" >> "$GITHUB_OUTPUT"
+            fi
+            exit 0
+          fi
+
+          # for a file, we know it was relocked
           echo "relocked=true" >> "$GITHUB_OUTPUT"
-        else
-          echo "relocked=false" >> "$GITHUB_OUTPUT"
+          exit 0
         fi
+
+        # if we get here then it did not relock
+        echo "relocked=false" >> "$GITHUB_OUTPUT"