How can I use GitHub Actions to concatenate a multiline file?

You can concatenate a multiline file using GitHub Actions by utilizing shell commands within a workflow. The core idea involves reading the file line by line and merging them into a single string.

Here is how you can achieve this, using different methods:

Method 1: Using 'cat' command and direct echo to a variable

The cat command displays the file and can redirect its output to create or overwrite a variable which contains all the content of the file in one line, then with additional worklow actions this content can be redirected to other steps or another variable:

Here's an example workflow snippet: name: Concatenate Multiline File
on:
  push:
    branches: [ main ]
jobs:
  concatenate_file:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v3

      - name: Concatenate file into one variable
        run: |
          CONCATENATED_CONTENT=$(cat your-multiline-file.txt | tr '\n' ' ')
          echo "CONCATENATED_CONTENT=$CONCATENATED_CONTENT" >> $GITHUB_ENV
      - name: Example of the variable
        run: echo "$CONCATENATED_CONTENT"


Here, the key part is cat your-multiline-file.txt | tr '\n' ' ':

• cat your-multiline-file.txt displays the content of the target file.
• tr '\n' ' ' converts all newline characters (\n) to spaces (' '). This is an efficient method if spaces as separator will be enough.
• The output is then captured into a bash variable CONCATENATED_CONTENT and finally assigned to GITHUB_ENV so it is acessible by later workflow steps
• A further example show how can we echo out the content of this variable, to ensure that is the result that we want to obtain

Method 2: Using a multi-line string in environment variable and other string based techniques
If you need something more elaborate, you could achieve similar effect creating variables directly and processing their contents as needed

Here's a snippet which can act as starting point : name: Concatenate Multiline File with MultiLine String
on:
  push:
    branches: [ main ]
jobs:
  concatenate_file:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v3

      - name: Read Multiline file as Variable
        run: |
          FILE_CONTENT="$(< your-multiline-file.txt )"
          echo "FILE_CONTENT=$FILE_CONTENT" >> $GITHUB_ENV

      - name: Clean up file with replace in string
        run: |
          CLEANED_CONTENT="${{ env.FILE_CONTENT }}"
          CLEANED_CONTENT="${CLEANED_CONTENT//$'\n'/ }"
          echo "CLEANED_CONTENT=$CLEANED_CONTENT" >> $GITHUB_ENV

      - name: Output Final Result
        run: echo "Final Result: ${{ env.CLEANED_CONTENT }}"


This example uses bash syntax:

• $(< your-multiline-file.txt ): reads file content into bash variable FILE_CONTENT
• We then create new workflow variable CLEANED_CONTENT from existing content with substitution of \n characters
• In a subsequent step, the result will be echoed using github actions specific sintax, accessing environmental variables with the specific expression ${{env.VAR}}.
• This process is more complex but shows alternative, using other kind of shell commands which are supported also from run: | execution environment

Ensure that your-multiline-file.txt exists in the repository in the location which your worklfow can acces. Adjust this command based on your actual use cases like file locations.

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