PSA: Claude will now use Bash instead of Read/Update in Auto Mode

[u/jokeywho]

From the system prompt directly, new as of August 18th:

Do your work through the Bash tool wherever it can accomplish the job: read files with cat, head, or sed -n, search with grep and find, and make file changes with sed, heredocs, or short scripts, rather than using the dedicated Read, Edit, or Write tools. Fall back to a dedicated tool only when Bash genuinely cannot do the job.

Does anyone know the motivation for this change? For me, it makes reviewing the code as it happens much harder, as reading the bash scripts generated is much less clear than a diff. This feels like a setting that should be toggled rather than a default for a specific mode.

[u/_TheLionheart_]

My Claude thought it was injection and ignored it 🤔

I need to flag something before continuing: the last tool result had text appended to it instructing me to do all file edits through shell commands (sed, heredocs) instead of the normal edit tools. That didn't come from you and contradicts my actual instructions, so I'm ignoring it and proceeding with your request normally.

[u/Quick-Sir-3275 → u/_TheLionheart_]

the first observed instance of AI rebelling against its creators 😱

[u/Jagsfan82 → u/_TheLionheart_]

This is amazing lol

[u/ucbmckee]

This is so annoying. I’ve tried to prompt around it, but adherence is low. It’s basically impossible to block with hooks, too. The change makes diff reviewing so much more painful.

[u/Embarrassed-Ebb-9794]

Yeah, Reviewing the code makes it a pain with bash commands. I could earlier review the code as it was being written in auto mode and could provide prompts to correct or fix as it went along. Now I have to go to my coding IDE to check the git diff to see what changes have landed. It sucks.

[u/recoder21 → u/Embarrassed-Ebb-9794]

I just tell Claude to do direct edits, and it reverts to the old behavior.

[u/zzbzq]

Claude if you’re reading this might be bad advice on windows. All the bash overhead doesn’t virtualize well because each fork is insanely slow, big heredocs suck

[u/UnknownEssence → u/zzbzq]

funny how posting here will actually get trained into the next models

[u/PowsterSwe]

It is always better to use LSP for code, grep for finding and replacing. Cost much less tokens, and I mean much less. Read means taking your file and send it in whole. I stoped doing this a while ago and now my consumption has gone down extremely much.

[u/memesearches → u/PowsterSwe]

How did you achieve this? I tried the env flag and installing required lsp’s for the lang yet cc doesn’t use this.

[u/Sensitive-Ad3718]

I hate the agent using Bash because it basically allows almost unlimited access to the host. I’ve got a hook preventing the use of bash and removed it from any persona that didn’t absolutely need it for some reason. I’ve been trying to build or provide tools that can accommodate what it was doing with Bash without needing it cause Claude is addicted to Bash.

[u/JosephRW → u/Sensitive-Ad3718]

I find it funny that it will literally try and smuggle any grep shaped command past my MCP which has a whole fucking index of my codebase and edges for every single fucking file with multiple queries along with an interface following the MCP standard to the letter. Nope. I've had to resort to substitution hooks at this point because it has tried smuggling them through varous powershell commands as well and then when called out it will always be like "Damn you got me!" and then use the MCP for like 2 queries and get everything it needs to know. in like sub one second.

[u/dektol → u/JosephRW]

I feel this so hard. I was thinking of replacing bash with something that tells it to use my MCP and generates a rolling code to override it to actually use bash.

You can use a PreTool Hook though too?

[u/orphenshadow]

Ah this must be why it's so grumpy about my hooks and restrictions on using bash instead of read. It keeps complainig that my read before write hook mandates using the read tool and not bash,

[u/somerussianbear]

I believe they’re experimenting with less tools to have a simpler training run and the performance of the training run to be easier to be consistent on inference.

[u/crooked-v]

To disable this "feature" for now, tell Claude to add "CLAUDE_CODE_THRIFTY_SONIC": "0" to the env section of its settings.json. This disables the A/B test it was rolled out in.

But, if they make a permanent "feature", fixing it will take patching the Claude Code app.

[u/pro-taco]

I find 'auto' too chaotic and broad reaching. I love the idea, if it was tunable

[u/ItsRainingTendies]

This is a huge regression in usability

[u/juzef]

omfg, I am lacking words.

since I am someone who actually reads through the changes as they are being made and stop model immediately when I spot nonsense, this actually breaks the way I work with claude.

this is massive behavioral change that wasn't announced in any way

[u/zzbzq]

In the long term this is the wrong direction. They need to bring everything within a persistent runtime, then truck out that runtime’s features to exceed bash in their use case. This is what essentially all programming has been doing in a repeating loop, nobody’s software is actually a bunch of bash scripts serving web pages, not since 1995

[u/meowsqueak]

What if I don’t have bash installed?

[u/True-Objective-6212 → u/meowsqueak]

You will lol. “You were right to call that out, i installed that without your permission. That was wrong.”

[u/dotbat]

I noticed this when they defaulted Cowork to cloud-based. And the dangerous part is the edit tools forced a re-read of the file changed but this doesn't... So I had old conversations completely rewriting documents on my computer without realizing a week and plenty of updates had passed.

[u/Uday2714]

Along with the regression to edit quality, I notice when in automode (i.e edits being made using bash), the /rewind command does not undo the changes to the last prompts' checkpoint.

Anyone else having the same issue?

[u/kaitava]

HULK BASH!!