Git has a nice feature called grep, when you want to get a commit for an old code, and it's a kind of search, but not enough for me !
I wrote a bash script to search for a "piece of code" inside a git project history whatever the branch and time.

It can :

Search a word and return the list of commits where the word was found.
Switch the project to the target commit, open the file at the specified line, for you, to copy your code, then restore yourself to your working branch !

If we save the file as ./gf.sh, we give execution rights chmod +x ./gf.sh and we add it in our .bashrc as an alias : alias gf=${HOME}/gf.sh.

We can wrote interesting command easily.

Example :

$ gf search 'vieux code'
$ gf open 'commit-id:fichier:ligne'

This is how the code looks :

#!/bin/bash
# by d4rk3r

# A smart way to search for a code
# inside your git history whatever the branch you're

# -- Setup :
# -- After getting the bash script

# chmod +x /path/to/gf.sh 
# -- to add the execute right to the script
# -- You can add it to your .bashrc env

# gf s 'pattern' -- to search for some code
# -- then after copy the line of the commit,

# gf o commit_id:line:file_name....
# -- gf will switch to that commit and open the line where the code is,
# -- after quitting, gf will restore your repo to the precedent branch where you were working

_git_search(){
    # a smart git command to get commit, file and line where
    # the string is available
    git rev-list --all | (
        while read revision; do
            git grep -n -F ${1} $revision
        done
    ) > ${HOME}/.gf-out
}

_search(){
    echo "[-] Searching for '${1}' in this repo..."
    sleep 2
    # We less in the list of results
    _git_search "${1}"
    cat ${HOME}/.gf-out | less
}

_open_code(){
    # getting your current branch
    branch=$(git branch | sed -n -e 's/^\* \(.*\)/\1/p')

    # A smart split from the incomming $1 parameter
    arr=($(echo "$1" | tr ':' '\n'))
    commit=${arr[0]}
    file=${arr[1]}
    line=${arr[2]}

    # some verbose
    echo "[-] Moving on commit : $commit"
    sleep 1
    echo "[-] Moving on file : $file"
    sleep 1
    echo "[-] Moving on line : $line"
    sleep 1

    # A checkout on the commit then a less on the line of the file
    git checkout "$commit"
    less +"$line" "$file"

    sleep 2
    echo "\n[-] Rolling back to your precedent branch..."
    # comming back to reality
    git checkout "$branch"
}

_help_commands(){
    echo "[-] gf help center:"
    echo "[-] gf s 'search-kwy-word'"
    echo "[-] gf o 'commit-id:line:file-name'"
}

main(){
    echo "[-] gf started..."

    if [ "$1" == "search" ] || [ "$1" == "s" ]; then
        _search $2
    elif [ "$1" == "open" ] || [ "$1" == "o" ]; then
        _open_code $2
    else
        echo "[x] Error: Bad parameter provided..."
        _help_commands
    fi
}

main $1 $2

Source code : Gist-Code

Have FUN !

git search for code whatever the branch, the time or the commit