Delete all the git branches but "master", "main", current branch, and every branch name you provide as argument.

git_branch_delete_all_but.sh

#!/bin/sh

function git_branch_delete_all_but() {
    branch_names_to_keep=("$@")
    branch_names_to_keep+=("master") # do not delete master
    branch_names_to_keep+=("main") # do not delete main
    branch_names_to_keep+=$(git symbolic-ref --short -q HEAD) # do not delete current branch

    branch_names_to_delete=()

    for branch_name in $(git for-each-ref --format='%(refname:short)' refs/heads/); do
        if [[ ! " ${branch_names_to_keep[*]} " =~ " ${branch_name} " ]]; then
            branch_names_to_delete+=$branch_name
        fi
    done

    for branchName in "${branch_names_to_delete[@]}"
    do
        git branch -D $branchName
    done
}