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Bad interpreter or CRLF script error

Inspect the shebang and line endings before rewriting scripts or changing execute permissions.

Safest first command

head -1 script.sh | cat -v

Before you run this

Expected output: A shebang line; CRLF line endings may show a trailing ^M at the end of the interpreter path.

When not to use it: Do not rewrite line endings on vendor, generated, or signed files until you know the file owner and deployment source.

Expected output example

#!/bin/bash^M

How to read the result

A `^M` at the end of the shebang means the kernel may look for `/bin/bash `, causing bad interpreter errors.

What to check next

Shebang ends with ^M

Means: The script likely has Windows CRLF line endings.

Next step: Confirm file type and CRLF locations before conversion.

Show Hidden CRLF in a Script Shebang

file reports CRLF terminators

Means: Line endings are probably the cause.

Next step: Inspect scope before converting.

Detect Script Line Endings with file

No CRLF found

Means: The interpreter path, executable bit, or mount options may be wrong instead.

Next step: Check permissions and interpreter path.

Find CRLF Lines in a Script

Bad interpreter decision tree

Read the first line, confirm line endings, then decide whether conversion is safe. A chmod fix will not repair a shebang that points at an interpreter name with a hidden carriage return.

  1. head -1 script.sh | cat -v
  2. file script.sh
  3. grep -n $'\r' script.sh | head

Bad fixes to avoid

Do not chmod recursively. Do not rewrite every script in a repository without checking generated files, vendored files, and version-control state.

Common causes

  • CRLF line endings copied from Windows
  • Wrong interpreter path
  • Script not executable
  • Mounted filesystem blocks execution

What not to change yet

  • Do not run dos2unix across a tree without review.
  • Do not chmod -R to fix one script.
  • Do not edit package-managed scripts in place before checking the package owner.

Stop and escalate if

  • The next step could interrupt users, remove data, or lock out access.
  • The output includes secrets, customer data, or private infrastructure details.
  • You cannot explain the blast radius of the repair command.

supporting commands

Command path

Guides and drills