echo-eval

This library simply prints a bash command with a shell prompt in front of it and then runs that command using eval. This pattern makes your shell scripts easier to debug because you can see which commands are being run and what the output is in a way that is familiar and approachable to you and your customers.

Index

1. Background
2. Installation
   1. bpkg - package manager
   2. make
   3. Manual Installation
3. Usage
   1. Security
4. Development
   1. Lint
   2. Test
   3. CI
5. See Also

Background

The name comes from a syntax I have used in BASH scripts to print significant or complex commands before running them to provide insight into what a script is doing for more technical users and customers, or for debugging.

echo "$ ls -la"
eval "ls -la"

The commands are displayed in the terminal in a way that looks like shell history, as if a human had sat at the terminal, typed the command, and run it.

$ ls -la
total 60
drwxrwxr-x 4 zach zach  4096 Feb  6 10:42 .
drwxrwxr-x 6 zach zach  4096 Feb  1 18:55 ..
-rw-rw-r-- 1 zach zach   563 Feb  6 01:31 bpkg.json
-rwxrwxr-x 1 zach zach   303 Feb  6 10:59 ee.sh
-rwxrwxr-x 1 zach zach 11824 Feb  6 10:44 ee.test.bats
drwxrwxr-x 8 zach zach  4096 Feb  6 10:59 .git
drwxrwxr-x 3 zach zach  4096 Feb  6 01:31 .github
-rw-rw-r-- 1 zach zach   358 Feb  5 21:05 .gitignore
-rw-rw-r-- 1 zach zach  1068 Feb  1 18:55 LICENSE
-rw-rw-r-- 1 zach zach   455 Feb  6 01:34 Makefile
-rw-rw-r-- 1 zach zach  8647 Feb  6 11:23 README.md

I find this is much more approachable to newer developers than something like set -x, which displays a bunch of nonsense in addition to the commands being run on most systems.

The logical next step was to de-duplicate the command so what is printed could never be different than what is being run.

DOCKER_RUN='docker run -it ubuntu:20:04'
echo "$ $DOCKER_RUN"
eval "$DOCKER_RUN"

This is a pain to type for all the major commands a script is doing and makes the source file thrice as many lines long.

The solution to this toil was to de-duplicate the pattern itself using a BASH function so that commands only take one line each again.

ee 'docker run -it ubuntu:20:04'

Finally, the function has been packaged as a module that can be installed on a system or imported by BASH scripts using a package manager.

Installation

You can install this script using a package manager (recommended), install manually and source it from somewhere, or invoke it directly without installing. This tool has no dependencies by design.

bpkg

This is the recommended installation method. Install bpkg if you have not already. Then, you have three installation options.

1. Install as a dependency for your BASH script. From the root of your project repo:

   bpkg install kj4ezj/echo-eval

   This will create a deps/ folder in the current directory with the following structure.

   deps
   ├── bin
   │   └── ee -> /deps/echo-eval/ee.sh
   └── echo-eval
       ├── bpkg.json
       └── ee.sh
   

   You can source one or more dependencies in your script from ./deps/bin/.
   • Be sure to add deps to your .gitignore.
   • If you package your project, be sure to declare this as a dependency in your bpkg.json file.
2. Install globally for the current user.

   bpkg install -g kj4ezj/echo-eval

3. Install globally for all users on the current system.

   sudo bpkg install -g kj4ezj/echo-eval

Note

At the time of writing, bpkg does not have a global uninstall. You can uninstall by deleting the relevant executable.

EE_PATH="$(which ee || ee 'echo "${BASH_SOURCE[0]}"' | tail -1)"
rm -f "$EE_PATH" 2>/dev/null || sudo rm -f "$EE_PATH"

make

Clone this repo locally using your preferred method. Navigate to the root of the repo in your terminal and install.

sudo make install

This will install ee for all users. If you do not wish to use sudo or otherwise install using root permissions, please install using bpkg.

Do the reverse to uninstall. From the root of this repo in your terminal:

sudo make uninstall

Manual Installation

You can also source this script in your ~/.bashrc or similar.

source ~/github/kj4ezj/echo-eval/ee.sh

Just remove that line to "uninstall."

Usage

This library takes the input you give it, prints or echoes it to the terminal with a fake shell prompt in front of it, then tries to run it as a command. For example, the output of this...

ee uname

...looks like this on Linux.

$ uname
Linux

You can invoke ee as a function...

echo-eval$ ee echo test
$ echo test
test

...or as a file.

echo-eval$ ./ee.sh echo test
$ echo test
test

Some commands may need to be encased in quotes to work the way you intend. For example, dc is sensitive to whitespace.

echo-eval$ ./ee.sh dc -e '1 2 + p'
$ dc -e 1 2 + p
dc: Could not open file 2
dc: Could not open file +
dc: Could not open file p
echo-eval$ ./ee.sh "dc -e '1 2 + p'"
$ dc -e '1 2 + p'
3

In this example, we want the input to ee to include the pipe (|).

echo-eval$ export EXAMPLE='yeet'
echo-eval$ ee printf "$EXAMPLE" | wc -c
18

BASH evaluated "$EXAMPLE", invoked ee with the input printf yeet, ee returned this...

$ printf yeet
yeet

...then BASH piped both those lines to wc -c, giving eighteen characters. Instead, we want to put quotes around the entire command.

echo-eval$ ./ee.sh 'printf "$EXAMPLE" | wc -c'
$ printf "$EXAMPLE" | wc -c
4

Here, "$EXAMPLE" is evaluated at runtime inside the library and we get the correct output of four characters.

Security

When you evoke echo-eval (ee) from a script or program, it:

1. Inherits the privileges of your script or program.
2. Runs in the context of your script or program.
3. Takes the input as a string and parses it, looking for commands to run.

This means you need to be wary of command injection, variable manipulation, and privilege escalation. Never, ever pass unsanitized user input to echo-eval, even if it is inside a print statement or in single quotes! All attack vectors associated with the eval command apply, known and unknown. You have been warned.

Development

Contributors need these tools installed.

• act
  • Requires docker.
• bashate
• bats
• bpkg
  • git
  • make
• dc
• git
• shellcheck

Please sign your commits.

Lint

This project uses bashate and shellcheck for linting. You can run the lint script directly...

./lint.sh

...or run the linters with bpkg.

bpkg run lint

They both do the same thing.

Test

This project uses the BASH Automated Testing System (BATS). Various issues currently prevent bpkg from installing BATS as a dependency, so you need to install it on your system for now.

This project has two types of tests:

• ee.test.bats - small and medium tests
• large-test.bats - large tests

The small tests can be invoked directly...

./ee.test.bats

...or you can run them with bpkg.

bpkg run test

The bpkg alias calls test.sh, which runs the small tests every time and will run the large tests if it detects a cloud-based CI environment. The large tests try to install the current commit from GitHub using bpkg, so you won't ever run them locally.

CI

This repo contains the following GitHub Actions workflow(s) for CI:

• echo-eval CI - initialize, lint, and test the echo-eval project.
  • Pipeline
  • Documentation

You can run the GitHub Actions workflow(s) locally using act.

act --artifact-server-path .github/artifacts

This, too, has a bpkg alias so nobody has to memorize it.

bpkg run act

Please make sure pipeline changes do not break act compatibility.

See Also

• bpkg
  • echo-eval on bpkg
  • GitHub > listing

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