Git squash extension. Put this file on /usr/local/share/git-squash/git-squash on most unix distribs

git-squash

#!/bin/bash
# Author: Joel Nothman
# Optimized by Pierstoval
# Under BSD-2 license
# See https://github.com/jnothman/git-squash
# See https://github.com/Pierstoval/git-squash

usage() {
    echo ""
    echo Usage: git squash '[-m <commit msg>] [-a|--append] [-f|--full] <base>'
    echo "  -m <commit msg>   Used to provide a new message for the squashed commit"
    echo "  -a                If specified, the commit msg will be followed by all squashed commits informations"
    echo "  -f|--full         If '-a|--append' is specified, all the messages will contain more informations (author, date...)"
    exit 1
}

unset base
unset message
unset append

full=false
base=""
append=false
appendMessage=""
commitsCount=0
message=""

while [ -n "$1" ]
do
    case "$1" in
        -h)
            usage
            ;;
        -m)
            shift
            if [ -z "$1" ]
            then
                echo '-m requires an argument' >&2
                usage
            fi

            if [ -n "$message" ]
            then
                message+=$'\n\n'"$1"
            else
                message="$1"
            fi
            ;;
        -f|--full)
            full=true
            ;;
        -a|--append-message)
            append=true
            ;;
        *)
            if [ -z "$base" ]
            then
                base="$1"
            else
                echo 'Multiple bases specified' >&2
                usage
            fi
    esac
    shift
done
if [ -z "$base" ]
then
    echo 'No base ref provided' >&2
    usage
fi

if [ "$append" = true ]
then
    nl=$'\n'
    commitsCount=`git rev-list ${base}..HEAD --count`
    if [ "$commitsCount" -eq "0" ]
    then
        echo "No commit for base '$base'."
        exit 1
    fi
    appendMessage+=$'\n'
    appendMessage+=$'\n'
    if [ "$full" = true ]
    then
        appendMessage+=`git log --pretty=format:"[%h] %ad - %cn <%ce>$nl%s$nl%b" -n${commitsCount}`
    else
        appendMessage+=`git log --pretty=format:"[%h] %s %b" -n${commitsCount}`
    fi
fi

seq_ed="$(mktemp -t squash_edXXXXXX)" &&
echo '#!'$(which bash)'
    echo Squashing... >&2
    tmp="$(mktemp -t squash_outXXXXXX)"
    awk '"'"'NR != 1 { sub(/^pick/, "squash") } {print}'"'"' "$1" > "$tmp"
    mv "$tmp" "$1"
' > $seq_ed &&
chmod +x "$seq_ed" &&

echo 'Warning: Forgetting local history. To revert, use:
  $ git reset --hard' $(git rev-parse --short HEAD) >&2

if [ -n "$message" ]
then
    GIT_SEQUENCE_EDITOR=$seq_ed GIT_EDITOR=touch git rebase -i $base
else
    GIT_SEQUENCE_EDITOR=$seq_ed git rebase -i $base
fi
if [ -n "$message" ]
then
    echo 'Updating commit message' >&2
    git commit --amend -m "$message$appendMessage" | head -n1
fi
rm -r "$seq_ed"