Why sh -c "cd dir && pwd" Prints the Wrong Directory

The Problem

While working in a Linux environment, I ran into a puzzling behavior. My home directory is /home/user, and there is a backend/ subdirectory under it. I expected the following command to print /home/user/backend:

sh -c "cd backend/ && pwd"

But it printed /home/user instead — as if cd never happened.

Ruling Out Common Mistakes

1. Is && Being Parsed by the Parent Shell?

A classic mistake is accidentally closing the quotes before &&:

# WRONG — pwd runs in the parent shell
sh -c "cd backend/" && pwd       # prints /home/user

# CORRECT — both commands run inside the child shell
sh -c "cd backend/ && pwd"       # should print /home/user/backend

I double-checked: my quotes were correct. Both cd and pwd were inside the quoted string passed to sh -c.

2. Does the Directory Exist?

Yes. ls backend/ worked fine, and cd backend/ alone produced no errors.

The Clue

After some experimentation, I discovered that adding any external command before cd && pwd fixed the output:

sh -c 'ls backend && cd backend/ && pwd'
# Correctly prints /home/user/backend

Simply prepending ls (an external binary at /bin/ls) made pwd report the right directory. This pointed to something deeper than a typo.

Root Cause: dash Builtin Optimization

On many Linux distributions (Debian, Ubuntu, etc.), /bin/sh is symlinked to dash, a lightweight POSIX shell. You can verify this:

ls -la /bin/sh
# lrwxrwxrwx 1 root root 4 ... /bin/sh -> dash

dash has an optimization for commands passed via sh -c: when the entire command chain consists of only shell builtins (cd and pwd are both builtins), dash takes a fast path that avoids forking a full subshell process. Unfortunately, this optimization path has a known issue where cd does not properly update the internal state that pwd reads from.

When an external command like ls is present in the chain, dash is forced to take the normal execution path, which correctly updates the working directory state after cd.

Workarounds

Any of the following will produce the correct output:

# 1. Use bash instead of sh
bash -c 'cd backend/ && pwd'

# 2. Use the external pwd binary instead of the builtin
sh -c 'cd backend/ && /bin/pwd'

# 3. Insert any external command to break the all-builtin optimization
sh -c 'true && cd backend/ && pwd'   # if true is external
sh -c 'ls backend && cd backend/ && pwd'

Takeaway

  • On systems where /bin/sh is dash, be aware that sh -c with pure-builtin command chains may behave unexpectedly.
  • When in doubt, use bash -c or call /bin/pwd explicitly.
  • This is a subtle difference between bash and dash that can silently produce wrong results in scripts and CI pipelines.