rebase-atop

#!/bin/bash

# $1: reference branchname to rebase the current branch's commit's atop

die() { printf %s "${@+$@$'\n'}" 1>&2 ; exit 1 ; }
see() ( { set -x; } 2>/dev/null ; "$@" )

name_eq_notional_master() { test "$1" = 'master' || test "$1" = 'main' ; }
local_branch_exists()  { git show-ref --verify --quiet "refs/heads/$1"; }
remote_branch_exists() { git show-ref --verify --quiet "refs/remotes/origin/$1"; }
tag_exists()           { git show-ref --verify --quiet "refs/tags/$1"; }

set -e  # Exit immediately if a command exits with a non-zero status.

git rev-parse --is-inside-work-tree >/dev/null 2>&1 || die "Error: Not in a Git repository"

current_branch="$(git branch --show-current)" ; test "$current_branch" || die "Error: no current branch in a Git repository???"
src_br="$current_branch"            # branch assumed to have my recent changes
dst_br="$1" ;     test "$dst_br" || die "missing only param, dest shared branch name"
test "$dst_br" != "$src_br" || die "ref & src branches cannot be the same!"

remote_branch_exists "$dst_br" || die "#2 param, dest shared branchname, has not remote"  # might be irrelevant

# Update "$dst_br" main
see git checkout "$dst_br"    || die "switching to $dst_br FAILED???"
see git pull origin "$dst_br" || die "pulling latest $dst_br from remote FAILED???"

# Before rebase:
# A---B---C (main/"$dst_br")
#      \
#       D---E (dev/"$src_br")
#

see git checkout "$src_br" || die "switching to $src_br FAILED???"
see git rebase "$dst_br"   || die "rebasing $src_br commits atop $dst_br FAILED!!!"

# After rebase:
# A---B---C (main/"$dst_br")
#          \
#           D'---E' (dev/"$src_br")