Checkout master, pull, checkout previous current branch, merge master into it.

git-merge-master.sh

#!/bin/bash

# Save the current branch name
current_branch=$(git rev-parse --abbrev-ref HEAD)
if [ $? -ne 0 ]; then
    echo "Error: Failed to get the current branch name."
    exit 1
fi

# Set target branch to 'master' or the provided argument
target_branch=${1:-master}

# Checkout the target branch
git checkout "$target_branch"
if [ $? -ne 0 ]; then
    echo "Error: Failed to checkout $target_branch."
    exit 1
fi

# Pull the latest changes
git pull
if [ $? -ne 0 ]; then
    echo "Error: Failed to pull the latest changes on $target_branch."
    git checkout "$current_branch"
    exit 1
fi

# Checkout the original branch
git checkout "$current_branch"
if [ $? -ne 0 ]; then
    echo "Error: Failed to checkout $current_branch."
    exit 1
fi

# Merge the target branch into the current branch
git merge "$target_branch" --no-edit
if [ $? -ne 0 ]; then
    echo "Error: Failed to merge $target_branch into $current_branch."
    exit 1
fi

echo "Merge of $target_branch into $current_branch completed successfully."