[Bug] Claude Code overrides user default SHELL environment variable

[smartwatermelon]

Bug Description
Claude Code overrides user default SHELL

Environment Info

• Platform: darwin
• Terminal: iTerm.app
• Version: 2.1.37
• Feedback ID: 09397305-34ef-462a-9b70-204f85b7b9bd

Claude Code Shell Investigation

Problem

Claude Code sessions were using /bin/zsh despite the developer machine being configured entirely for bash.

Environment

• Login shell (dscl): /opt/homebrew/bin/bash (GNU Bash 5.3.9)
• /etc/shells: /opt/homebrew/bin/bash is listed
• User's actual shell usage: Always bash, never zsh
• Claude Code session shell: /bin/zsh (5.9)

Root Cause

Claude Code has its own shell detection logic that does not simply read the user's login shell from dscl or honor $SHELL as set by the login process. Its automatic detection was resolving to /bin/zsh — likely because macOS defaults to zsh since Catalina, and Claude Code's detection logic may prioritize the system default over the user's configured login shell.

Fix

Added CLAUDE_CODE_SHELL to ~/.claude/settings.json:

{
  "env": {
    "CLAUDE_CODE_SHELL": "/opt/homebrew/bin/bash"
  }
}

This environment variable explicitly tells Claude Code which shell to use for all Bash tool invocations, overriding the automatic detection.

Implications

• The current session (at time of fix) continues using zsh — restart required
• All future sessions will use /opt/homebrew/bin/bash
• Shell-specific syntax differences (e.g., shopt in bash vs setopt in zsh, array indexing, BASH_SOURCE vs ZSH_EVAL_CONTEXT) may have caused subtle issues in prior sessions
• The BASH_ENV setting in settings.json (pointing to ~/.config/bash/functions.sh) was likely not being sourced correctly under zsh, since BASH_ENV is a bash-specific variable

Related Settings

Variable	Purpose
CLAUDE_CODE_SHELL	Override shell binary for Bash tool
CLAUDE_CODE_SHELL_PREFIX	Wrap all bash commands with a prefix
CLAUDE_BASH_MAINTAIN_PROJECT_WORKING_DIR	Return to project dir after each command

[github-actions]

Found 3 possible duplicate issues:

1. Bash tool does not respect user's default shell (uses zsh instead of fish) #11475
2. [FEATURE] Allow users to configure which shell the Bash tool uses or inherit initial shell #7490
3. Bash tool misleadingly executes in user's default shell instead of actual bash #2444

This issue will be automatically closed as a duplicate in 3 days.

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🤖 Generated with Claude Code

[smartwatermelon]

Not a duplicate, though related.

[github-actions]

Closing for now — inactive for too long. Please open a new issue if this is still relevant.

[github-actions]

This issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.