A script to easily "docker exec" into a running Docker container

docker-shell

#!/bin/bash
# easily "docker exec" into a running Docker container
# latest version: https://gist.github.com/ljm42/2b3bfd8ff886015bbce8

# for unRAID, place this script on your flash drive as /boot/custom/docker-shell
# then add this to your go script (without the leading pound sign):
# cp /boot/custom/docker-shell /usr/local/bin

CONTAINERS=`docker ps | awk 'NR==1 {offset=index($0,"NAMES")};NR>1{print substr($0,offset)}' | sort -f | tr "\n" " "`

echo
echo "Choose a Docker container:"
i=1
for container in $CONTAINERS
do
 echo "$((i++)) : $container"
done

read MYCHOICE
CHOSEN=`echo $CONTAINERS | cut -d' ' -f$MYCHOICE 2>/dev/null`

if [ "$CHOSEN" = "" ]; then
  echo Invalid option
  exit
fi

# try running bash, if exit code 126 then try running sh
for SHELL in bash sh
do
  clear
  echo " "
  echo -e '\E[30;42m'"\033[5m    $CHOSEN - $SHELL   \033[0m"
  echo  " "
  tput sgr0
  docker exec -it $CHOSEN $SHELL
  if [ $? -ne 126 ]; then
    break
  fi
done

Maybe I'am wrong, but if the container has only sh and not additionally bash, this script wont work.
I get an error and the execution ist stopped.

Is is an "php:8.4.18-fpm-alpine3.23" image and alpine does not have bash (without explicit installation). (only sh)

docker-playground-php-fpm-1 - bash

OCI runtime exec failed: exec failed: unable to start container process: exec: "bash": executable file not found in $PATH
# 

Is there a way to safely detect available shell in container?

I fixed this and since you're having the the same issue here is my fix. There are also some formatting changes so feel free to not incorporate those if you prefer the previous style.

I also added an automatic PUID and PGID detector so it doesn't just open a shell as root anymore.

#!/bin/bash
# easily "docker exec" into a running Docker container

# for unRAID, place this script on your flash drive as /boot/custom/docker-shell
# then add this to your go script (without the leading pound sign):
# cp /boot/custom/docker-shell /usr/local/bin

# Use Docker's built-in formatting to get container names cleanly
CONTAINERS=$(docker ps --format '{{.Names}}' | sort -f)

if [ -z "$CONTAINERS" ]; then
  echo "No running Docker containers found."
  exit 1
fi

echo "Choose a Docker container:"
# Use the bash 'select' built-in to safely handle numbered menus
PS3="Enter a number: "
select CHOSEN in $CONTAINERS; do
  if [ -n "$CHOSEN" ]; then
    break
  else
    echo "Invalid option. Please try again."
  fi
done

# try running bash; if exit code 126 or 127 then try running sh
for SHELL in bash sh; do
  clear
  echo " "
  echo -e '\E[30;42m'"\033[5m    $CHOSEN - $SHELL   \033[0m"
  echo " "
  tput sgr0

  # Many unRAID containers drop privileges to PUID/PGID (LinuxServer)
  # or USER_ID/GROUP_ID (jlesage), so files created in the shell
  # are root-owned unless we do the same!
  ENV_VARS=$(docker inspect --format '{{range .Config.Env}}{{println .}}{{end}}' "$CHOSEN")
  PUID=$(echo "$ENV_VARS" | grep -E '^PUID=' | cut -d= -f2)
  PGID=$(echo "$ENV_VARS" | grep -E '^PGID=' | cut -d= -f2)

  # Fallback for jlesage containers (like MKVToolNix) which use USER_ID / GROUP_ID
  if [ -z "$PUID" ]; then
    PUID=$(echo "$ENV_VARS" | grep -E '^USER_ID=' | cut -d= -f2)
  fi
  if [ -z "$PGID" ]; then
    PGID=$(echo "$ENV_VARS" | grep -E '^GROUP_ID=' | cut -d= -f2)
  fi

  USER_ARG=""
  if [ -n "$PUID" ]; then
    if [ -n "$PGID" ]; then
      USER_ARG="-u $PUID:$PGID"
    else
      USER_ARG="-u $PUID"
    fi
    echo -e "  \E[32mSwitching to user $PUID${PGID:+:$PGID}\033[0m"
    echo " "
  fi

  # Note: $USER_ARG is intentionally unquoted here so it expands to either nothing or the -u flag
  docker exec $USER_ARG -it "$CHOSEN" "$SHELL"

  # You MUST save $? to a variable before checking multiple conditions!
  # Otherwise, the first [ ... ] check overwrites $? for the second check.
  EXIT_CODE=$?

  # 126 = Command invoked cannot execute
  # 127 = Command not found
  if [ $EXIT_CODE -ne 126 ] && [ $EXIT_CODE -ne 127 ]; then
    break
  fi
done