[BUG] Inconsistent Grep Results Between Direct Execution and Script Execution

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude Code's Bash tool produces different results when executing the same grep command directly versus through a shell script, and local bash.

What Should Happen?

Direct execution should return the same results as shell script execution and local bash.

Error Messages/Logs

No error messages - silent incorrect behavior.

Steps to Reproduce

1. Create a test file as follow.

implementation("line1")
implementation("line2")
implementation("line3")
testImplementation("line4")
testImplementation("line5")
runtimeOnly("line6")
compileOnly("line7")
developmentOnly("line8")
implementation("line9")
testImplementation("line10")

1. Execute test command by claude code (Direct execution)

grep -E "implementation|testImplementation|testRuntimeOnly|runtimeOnly|compileOnly|developmentOnly" simple_test.txt

• return (incorrect)

runtimeOnly("line6")
compileOnly("line7")
developmentOnly("line8")

1. Create a test shell script file as follow (test.sh)

#!/bin/bash
grep -E "implementation|testImplementation|testRuntimeOnly|runtimeOnly|compileOnly|developmentOnly" simple_test.txt

1. Execut test shell script file by claude code (Shell script execution)

Bash(./test.sh)

• return (correct)

 implementation("line1")
 implementation("line2")
 implementation("line3")
 testImplementation("line4")
 testImplementation("line5")
 runtimeOnly("line6")
 compileOnly("line7")
 developmentOnly("line8")
 implementation("line9")
 testImplementation("line10"

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

Unknown

Claude Code Version

2.0.9

Platform

Other

Operating System

Ubuntu/Debian Linux

Terminal/Shell

WSL (Windows Subsystem for Linux)

Additional Information

About claude code version :
First, I faced this problem on claude code 1.0.58. And upgrade to 2.0.9 but not fixed.

Workaround :
Execute complex grep commands through shell scripts rather than direct Bash tool execution:

# Instead of direct execution, create a script:
echo 'grep -E "pattern" file.txt' > temp_script.sh
chmod +x temp_script.sh
./temp_script.sh

More informatiln :

• Bug report generated by claude code : claude_code_bash_bug_report.md
• Test file generated by claude code : simple_test.txt simple_core_test.sh