Avoid duplication of code

Avoid duplication of code

[Yasuhiro KIMURA]

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

Re: Avoid duplication of code

[Jun. T]

> 2020/05/25 18:02, Yasuhiro KIMURA <yasu@utahime.org> wrote:
> 
> 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?

Suppose a parameter, say valname, contains a name of another parameter;

valname=SSH_AUTH_SOCK

Then you can GET the current value of SSH_AUTH_SOCK by

if [[ -n ${(P)valname} ]]; then ...

You can SET a new value to SSH_AUTH_SOCK in a couple of ways.
In your case, probably

export $valname='new value'

would be the simplest. If you don't want to export the variable, then,

: ${(P)valname::=new value}

Re: Avoid duplication of code

[Yasuhiro KIMURA]

Hello Jun,

Thank you for reply.

From: "Jun. T" <takimoto-j@kba.biglobe.ne.jp>
Subject: Re: Avoid duplication of code
Date: Mon, 25 May 2020 23:22:39 +0900

> Suppose a parameter, say valname, contains a name of another parameter;
> 
> valname=SSH_AUTH_SOCK
> 
> Then you can GET the current value of SSH_AUTH_SOCK by
> 
> if [[ -n ${(P)valname} ]]; then ...
> 
> You can SET a new value to SSH_AUTH_SOCK in a couple of ways.
> In your case, probably
> 
> export $valname='new value'
> 
> would be the simplest. If you don't want to export the variable, then,
> 
> : ${(P)valname::=new value}

I changed function definition as following.

----------------------------------------------------------------------
update_tmux_ssh_agent_environments () {
    if [ -z "${TMUX}" ]
    then
        echo "This function must be called inside tmux session."
        return -1
    fi
    for varname in SSH_AGENT_PID SSH_AUTH_SOCK
    do
        newvalue=$(tmux show-environment "${varname}" | sed -n "s/^${varname}=\(.*\)/\1/p")
        if [ -n "${(P)varname}" ]
        then
            if [ -z "${newvalue}" ]
            then
                unset "${varname}"
                echo "${varname} is cleared."
            elif [ "${(P)varname}" != "${newvalue}" ]
            then
                export "${varname}"="${newvalue}"
                echo "${varname} is updated."
            else
                echo "${varname} is unchanged."
            fi
        elif [ -n "${newvalue}" ]
        then
            export "${varname}"="${newvalue}"
            echo "${varname} is set now."
        else
            echo "${varname} stays unset."
        fi
    done
    return 0
}
----------------------------------------------------------------------

And now I can successfully update both SSH_AGENT_PID and
SSH_AUTH_SOCK.

---
Yasuhiro KIMURA

Re: Avoid duplication of code

[Daniel Shahaf]

Yasuhiro KIMURA wrote on Thu, 28 May 2020 17:05 +0900:
> ----------------------------------------------------------------------
> update_tmux_ssh_agent_environments () {
>     if [ -z "${TMUX}" ]
>     then
>         echo "This function must be called inside tmux session."
>         return -1
>     fi

You might want to add «local varname» here.

>     for varname in SSH_AGENT_PID SSH_AUTH_SOCK
> }  
> ----------------------------------------------------------------------

Cheers,

Daniel

Re: Avoid duplication of code

[Yasuhiro KIMURA]

From: Daniel Shahaf <d.s@daniel.shahaf.name>
Subject: Re: Avoid duplication of code
Date: Thu, 28 May 2020 08:53:18 +0000

>> ----------------------------------------------------------------------
>> update_tmux_ssh_agent_environments () {
>>     if [ -z "${TMUX}" ]
>>     then
>>         echo "This function must be called inside tmux session."
>>         return -1
>>     fi
> 
> You might want to add «local varname» here.
> 
>>     for varname in SSH_AGENT_PID SSH_AUTH_SOCK
>> }  
>> ----------------------------------------------------------------------
> 
> Cheers,

Thank you for pointing out. I added 'local newvalue varname' at the
top of function definition.

---
Yasuhiro KIMURA