Bash tool: environment variables and command substitution break when piping

Description

Environment variables ($USER, $PWD, $HOME) and command substitution ($(whoami), backticks) become empty/fail when the bash command includes a pipe (|).

Reproduction

Works (no pipe):

echo "user is $USER"
# Output: user is myusername

echo "pwd is $(pwd)"
# Output: pwd is /home/myusername

Broken (with pipe):

echo "user is $USER" | head -1
# Output: user is
# (variable is empty!)

echo "user is $(whoami)" | head -1
# Output: (completely empty)

ls -la $(pwd) | head -5
# Output: (empty)

Workaround:

bash -c 'echo "user is $USER" | head -1'
# Output: user is myusername
# (works when wrapped in bash -c with single quotes)

Impact

This affects any piped command that uses variables or command substitution, e.g.:

• squeue -u $USER | head -10
• ps aux | grep $(whoami)
• find $HOME -name "*.txt" | head

Environment

• Claude Code version: 2.1.29
• OS: Ubuntu 22.04 (Linux 6.8.0-60-generic x86_64)
• Bash version: 5.1.16(1)-release

🤖 Generated with Claude Code