Fix chpwd error when DIRSTACKSIZE is unset by Claude Code

[MSch]

Add null check for DIRSTACKSIZE variable before numeric comparison to prevent shell errors when Claude Code unsets the environment variable.

🤖 Generated with Claude Code

[zeha]

hi @MSch, just wondering: when does Claude Code unset DIRSTACKSIZE?

[msch-nutrient]

@zeha I wish I knew. I've been observing chpwd:2: bad math expression: operand expected at `<= 0 ' from time to time when it's invoking the Bash tool (which actually runs $SHELL) and haven't been able to track down why exactly it happens. You could argue that in the age of vibe coding it's easier to add more slop / defensive coding everywhere to make up for whatever the AI may or may not do.

> Is the DIRSTACKSIZE env var set?

⏺ Bash(echo $DIRSTACKSIZE)
  ⎿  (No content)

⏺ No, the DIRSTACKSIZE environment variable is not set (empty value).

> which env vars are set

⏺ I'll check the environment variables that are currently set.

⏺ Bash(env | sort)
  ⎿  ANDROID_HOME=/usr/local/opt/android-sdk    
     ANDROID_NDK_HOME=/usr/local/opt/android-ndk
     BUNDLER_EDITOR=subl -n
     … +50 lines (ctrl+r to expand)

⏺ The key environment variables set are:

  - CLAUDECODE=1 - Indicates Claude Code CLI is running
  - CLAUDE_CODE_ENTRYPOINT=cli - Entry point mode
  - PATH - Includes various development tools and binaries
  - HOMEBREW_NO_AUTO_UPDATE=1 - Prevents Homebrew auto-updates
  - PNPM_HOME - pnpm package manager location
  - ANDROID_HOME/ANDROID_NDK_HOME - Android development paths
  - GOPATH - Go development workspace
  - Standard shell variables (HOME, USER, SHELL, PWD, etc.)

And yet:

% echo $DIRSTACKSIZE
20