[SOLVED] sed: replace immediate next word coming after a particular keyword

Issue

In GitHub actions, when merging a push request to main, I would like to replace the branch name occurrence in a notebook by main.

For instance, given the below line: git clone --branch fork1 https://somrepo.git

Using the below regex, all values till the end of the line are replaced, however, my intention is to simply replace fork1 by main:

sed -i 's/\(--branch\)\(.*\)/\1 main/'

Another example, given the below line: "https://colab.research.google.com/github/user/repo/blob/fork2/notebook.ipynb"

Using the below regex, all values till the end of the line are replaced, however, my intention is to simply replace fork2/ by main/:

sed -i 's/\(blob\/\)\(.*\)/\1 main\//'

EDIT:

To clarify my question, my github action use case is to replace the branch name by main in several files after merging a PR..And no, GITHUB_REF_NAME would not work in this case since the ref_name would point to the merge branch and not the initial branch where PR was created.

name: Update Branch Name

    on:
      push:
        branches:
          - main
    
    jobs:
      restore_main_branch_name:
        runs-on: ubuntu-latest
        
        steps:
        - name: Checkout code
          uses: actions/checkout@v4
          
        - name: Update .ipynb files
          run: |
            sed -i "s|${{ github.ref_name }}|main|g" colabLaunchScript.ipynb
    
            
        - name: Commit changes
          run: |
            git config --local user.email "[email protected]"
            git config --local user.name "GitHub Actions"
            git commit -am "Restore main branch name in .ipynb file"
            git push -u origin main

Solution

To replace the next non-space token after --branch, match --branch followed by one or more spaces, followed by the longest sequence of non-space characters.

sed 's/\(--branch  *\)[^ ]*/\1main/'

(If you have sed -E this can be simplified to

sed -E 's/(--branch +)[^ ]*/\1main/'

but this is a non-POSIX extension.)

Your attempt had .* which simply matches all characters up until the end of the line (i.e. any character . repeated as many times as possible *).

To match the next non-space, non-slash token after /blob/, match non-space, non-slash characters [^ /] as many as possible *; and probably use a different delimiter than slash to simplify things for yourself;

sed 's%\(/blob/\)[^ /]*%\1main%'

If you need the replacement string to come from a shell variable, you need to use double quotes instead of singne ones; this then requires you to use more backslashes in places where the shell will eat some of them. A simple workaround is to use a single-quoted string next to a double-quoted string so you don't need to add a boatload of backslashes;

sed 's%\(/blob/\)[^ /]*%\1'"$branch%"

The Stack Overflow regex tag info page has answers to common beginner questions and links to learning materials.

Answered By - tripleee

Answer Checked By - Dawn Plyler (WPSolving Volunteer)