sh: apt-get: not found is what the Alpine Linux container printed in the test when given an Ubuntu install command. Alpine installs packages with apk, not apt-get: replace apt-get update && apt-get install -y curl with apk add --no-cache curl and the install works.

Package names can differ from Ubuntu's too (Ubuntu's ping package is iputils-ping, Alpine's is iputils), so check them with apk search -x before you translate a whole list.

The error

docker run --rm alpine sh -c 'apt-get update'
sh: apt-get: not found

In a running Alpine container the exit code was 127:

docker exec fix10-lc-al2 sh -c 'apt-get install -y curl 2>&1; echo exit=$?'
sh: apt-get: not found
exit=127

Why it happens

The alpine image is Alpine Linux 3.24.2 here. Its sh is BusyBox, its package tool is apk, and there is no apt-get and no bash: 

docker exec fix10-lc-al2 sh -c 'cat /etc/alpine-release; ls -l /bin/sh; command -v apk apt-get bash; echo exit=$?'
3.24.2
lrwxrwxrwx    1 root     root            12 Sep 17 17:32 /bin/sh -> /bin/busybox
/sbin/apk
exit=0

command -v printed a path only for apk. An apt-get line copied from Ubuntu instructions therefore has nothing to run in this image.

The fix

docker exec fix10-lc-al2 sh -c 'apk add --no-cache curl 2>&1; echo apk-exit=$?; curl --version | head -1'
(1/9) Installing brotli-libs (1.2.1-r0)
...
(9/9) Installing curl (8.23.0-r0)
Executing busybox-1.37.0-r31.trigger
OK: 13.1 MiB in 25 packages
apk-exit=0
curl 8.23.0 (x86_64-alpine-linux-musl) libcurl/8.23.0 OpenSSL/3.5.8 zlib/1.3.2 brotli/1.2.1 zstd/1.5.7 c-ares/1.34.9 libidn2/2.3.8 libpsl/0.21.5 nghttp2/1.70.0

apk add --no-cache installed curl and its eight libraries without a separate update step. apk search -x confirmed the Alpine names of two network packages: 

docker exec fix10-lc-al2 sh -c 'apk search -x net-tools; apk search -x iputils'
net-tools-2.10-r3
iputils-20250605-r2

If a script you copy into the container starts with #!/bin/bash, bash has to be installed first, because the image has only BusyBox sh. One more apk add did it: 

docker exec fix10-lc-al2 sh -c 'apk add --no-cache bash 2>&1; echo apk-exit=$?; bash --version | head -1'
...
(4/4) Installing bash (5.3.9-r1)
...
apk-exit=0
GNU bash, version 5.3.9(1)-release (x86_64-alpine-linux-musl)

The mirror mistake

The opposite happens when an Alpine instruction meets an Ubuntu container: bash has no apk there. 

docker exec fix10-lc-u3 bash -c 'apk add curl 2>&1; echo exit=$?'
bash: line 1: apk: command not found
exit=127

Use apt-get update and apt-get install -y there. The line 1: part appears because the command ran through bash -c.

How it was reproduced

The captures used the cached alpine image (Alpine 3.24.2) and ubuntu:24.04 on Docker Engine 29.9.3: one docker run --rm alpine, a container started with docker run -d --name fix10-lc-al2 alpine sleep 3600 and one started with docker run -d --name fix10-lc-u3 ubuntu:24.04 sleep infinity. Every command was sent from Windows PowerShell 5.1 exactly as shown, with the sh -c and bash -c text in single quotes so it reached the container unchanged. The container names are the test's own.

Frequently asked

How do I install packages in an Alpine container?
Use apk add --no-cache followed by the package name. In the test apk add --no-cache curl returned 0 and curl --version worked.
Why is apt-get not found in my Docker container?
In the test the image was Alpine Linux, which has apk instead. command -v found /sbin/apk and no apt-get or bash.
Does Alpine have bash?
Not in the tested image; sh is BusyBox. In the test apk add --no-cache bash installed GNU bash 5.3.9.

More decoded errors in the Fixes category. For a missing tool in an Ubuntu container, see bash: ping: command not found.