Feat: Implement action to run a RegEx on a file with grep

Signed-off-by: Matthew Watkins <[email protected]>

.github/actions/file-grep-regex-action/README.md

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+<!--
+[comment]: # SPDX-License-Identifier: Apache-2.0
+[comment]: # SPDX-FileCopyrightText: 2024 The Linux Foundation
+-->
+
+# 📦 Action to run RegEx against a file using GREP
+
+Returns values from a text file using the command-line tool, grep.
+
+## file-grep-regex-action
+
+## Usage Example
+
+Call as a step in a larger composite action or workflow.
+
+<!-- markdownlint-disable MD013 -->
+
+```yaml
+steps:
+    - uses: lfit/releng-reusable-workflows/.github/actions/file-grep-regex-action@main # v1.0.0
+      id: grep-file
+      with:
+          # https://regex101.com/r/axPzef/1
+          flags: "-oP -m1"
+          regex: '(?<=^\[testenv:docs\])*basepython = python\K(.*)'
+          filename: "docs/tox.ini"
+          no_fail: "true"
+```
+
+<!-- markdownlint-enable MD013 -->
+
+## Inputs
+
+<!-- markdownlint-disable MD013 -->
+
+| Variable Name | Required | Default | Description                                           |
+| ------------- | -------- | ------- | ----------------------------------------------------- |
+| REGEX         | True     | N/A     | The regular expression to use                         |
+| FILENAME      | True     | N/A     | The text file to search with GNU grep                 |
+| FLAGS         | True     | N/A     | The flags passed to grep on the command line          |
+| NO_FAIL       | False    | False   | Do not exit (if file not found or no string returned) |
+
+<!-- markdownlint-enable MD013 -->
+
+## Outputs
+
+<!-- markdownlint-disable MD013 -->
+
+| Variable Name    | Mandatory | Description                                    |
+| ---------------- | --------- | ---------------------------------------------- |
+| EXTRACTED_STRING | No        | The string extracted by the regular expression |
+
+<!-- markdownlint-enable MD013 -->

.github/actions/file-grep-regex-action/action.yaml

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+---
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: 2024 The Linux Foundation
+
+name: "Extract string from file using GREP"
+description: "Uses grep and a regular expression to extract text from files"
+
+inputs:
+  # Mandatory
+  FLAGS:
+    description: "Flags to use with grep command"
+    required: false
+    default: "-E"
+  REGEX:
+    description: "Regular expression used to extract string"
+    required: true
+  FILENAME:
+    description: "File containing text to extract"
+    required: true
+  # Optional
+  NO_FAIL:
+    description: "Override errors if file not found or no value returned"
+    required: false
+    default: "false"
+
+outputs:
+  EXTRACTED_STRING:
+    description: "The string extracted by the regular expression"
+    value: ${{ steps.grep.outputs.extracted_string }}
+
+runs:
+  using: "composite"
+  steps:
+    - name: "Extract text/string from file"
+      id: grep
+      shell: bash
+      run: |
+        # Extract text/string from file
+
+        set -o pipefail
+
+        set -o noglob
+        FLAGS="${{ inputs.FLAGS }}"
+        REGEX='${{ inputs.REGEX }}'
+        FILENAME="${{ inputs.FILENAME }}"
+        set +o noglob
+
+        if [ ! -f "$FILENAME" ]; then
+          echo "Error: file not found [$FILENAME]"
+          if [ "${{ inputs.NO_FAIL }}" = "true" ]; then
+            exit 0
+          else
+            exit 1
+          fi
+        fi
+
+        set -o noglob
+        echo "Flags to grep command: $FLAGS"
+        echo "Regular expression to use: $REGEX"
+        echo "File to search: $FILENAME"
+        # Extract the string using grep and regex
+        STRING=$(grep $FLAGS '${{ inputs.REGEX }}' $FILENAME)
+        set +o noglob
+
+        if [ -z "$STRING" ]; then
+          echo "String extraction failed; no matching value found ❌"
+          if [ "${{ inputs.NO_FAIL }}" = "true" ]; then
+            exit 0
+          else
+            exit 1
+          fi
+        else
+          # Make string available as action output
+          echo "extracted_string=$STRING" >> "$GITHUB_OUTPUT"
+          echo "Extracted string: $STRING ✅"
+        fi