/usr/bin/env: 'python': No such file or directory

Quick fix

Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.

# Is there a python3 but no python?
command -v python3 python

# Check for CRLF line endings too (shows ^M at the end of the first line)
head -1 script.py | cat -A
sed -i "s/\r$//" script.py

# Best fix: make the shebang ask for what exists
sed -i '1s|^#!.*python$|#!/usr/bin/env python3|' script.py

# Or, on Debian and Ubuntu, provide the alias system-wide
sudo apt install python-is-python3

# Inside a virtualenv, python exists once it is activated
source .venv/bin/activate && python --version

How to diagnose Shell errors

Shell errors are usually about PATH, permissions, or quoting and expansion. The quoting class is the most damaging because it fails silently: an unquoted variable containing a space becomes two arguments, and an empty one disappears entirely. Running shellcheck over any script longer than a few lines catches most of these before they run.

If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.

1. Trace execution with bash -x script.sh to see each command after expansion. This makes quoting bugs immediately visible.
2. Start every script with set -euo pipefail so failures stop the script instead of cascading.
3. Quote every variable expansion: "$var", "${arr[@]}". This single habit prevents the majority of shell bugs.
4. Use command -v foo to check whether something is on PATH, and echo "$PATH" to see what the shell is actually searching.
5. In Makefiles, recipe lines must begin with a real tab character. "missing separator" always means spaces were used instead.

Tools worth reaching for

• shellcheck
• bash -x
• set -euo pipefail
• command -v
• cat -A (to reveal tabs)

Authoritative references

Primary documentation for this error, worth reading before applying any fix in production.

📖 peps.python.org 📖 man7.org

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