Avoid duplication of code

[Yasuhiro KIMURA <yasu@xxxxxxxxxxx>]

Hello All,

It may not directly be related to zsh but please help me improve my
code. There is following function definition in my .zshrc.

----------------------------------------------------------------------
01: update_ssh_auth_sock () {
02:    if [ -z "${TMUX}" ]
03:    then
04:        echo "This function must be called inside tmux session."
05:        return -1
06:    fi
07:    newval=$(tmux show-environment SSH_AUTH_SOCK | sed -n 's/^SSH_AUTH_SOCK=\(.*\)/\1/p')
08:    if [ -n "${SSH_AUTH_SOCK}" ]
09:    then
10:        if [ -z "${newval}" ]
11:        then
12:            unset SSH_AUTH_SOCK
13:            echo "SSH_AUTH_SOCK is cleared."
14:        elif [ "${SSH_AUTH_SOCK}" != "${newval}" ]
15:        then
16:            export SSH_AUTH_SOCK=${newval}
17:            echo "SSH_AUTH_SOCK is updated."
18:        else
19:            echo "SSH_AUTH_SOCK is unchanged."
20:        fi
21:    elif [ -n "${newval}" ]
22:    then
23:        export SSH_AUTH_SOCK=${newval}
24:        echo "SSH_AUTH_SOCK is set now."
25:    else
26:        echo "SSH_AUTH_SOCK stays unset."
27:    fi
28:    return 0
29: }
----------------------------------------------------------------------

I use this function to update environment variables related to
ssh-agent when I attaches tmux session that already exists before
login. Currently this function only update SSH_AUTH_SOCK but I would
like to change it so it also updates SSH_AGENT_PID. The easiest way is
to copy lines from 7 to 27, paste them after line 27 and replace
SSH_AUTH_SOCK with SSH_AGENT_PID. But if possible I would like to
avoid duplication of code. At first following 2 idea hit upon me.

1. Define function that updates single environment variable and pass
   variable name as argument of it.
2. Use 'for name in word; do list done' such as following.

      for valname in SSH_AUTH_SOCK SSH_AGENT_PID
      do
        (update value of environment variable named ${valname})
      done

But it seems that both require nested variable expansion and that it
is impossible. Then is there any other way to avoid code duplication?

Best Regards.

---
Yasuhiro KIMURA