Commands starting with "!" don’t always work

[christophberger]

Description

A Taskfile that worked fine for months is now failing when trying to evaluate an environment variable within a precondition.

This Taskfile works:

version: "3"

env:
  PORT: 1313

tasks:
  port:
    cmds:
      - echo $PORT

Output:

> task port
task: [port] echo $PORT
1313

This one fails:

version: "3"

env:
  PORT: 1313

tasks:
  noserverrunning:
    preconditions:
      - sh: "! nc -z localhost $PORT"
        msg: Port $PORT is not available.
  port:
    deps:
      - noserverrunning
    cmds:
      - echo $PORT

Output:

> task port
task: Port $PORT is not available.
task: precondition not met

Expected (if the precondition isn't met): Port 1313 is not available.

The Taskfile has been the same for months, but when I used it today, it started failing. Hence I assume it's a bug.

Version

3.44.1

Operating system

macOS Sequoia 15.5

Experiments Enabled

No response

Example Taskfile

version: "3"

env:
  PORT: 1313

tasks:
  noserverrunning:
    preconditions:
      - sh: "! nc -z localhost $PORT"
        msg: Port $PORT is not available.
  port:
    deps:
      - noserverrunning
    cmds:
      - echo $PORT

[vmaerten]

Hello !
You need to use the go templating system :

version: "3"

env:
  PORT: 1313

tasks:
  noserverrunning:
    preconditions:
      - sh: "! nc -z localhost {{.PORT}}"
        msg: Port {{.PORT}} is not available.
  port:
    deps:
      - noserverrunning
    cmds:
      - echo {{.PORT}}

[christophberger]

Thanks @vmaerten, I'll try this, but can you tell my why my version worked fine until just recently?

[christophberger]

Unfortunately, {{.PORT}} doesn't seem to work inside the sh command string (I tested the string with and without double quotes). I always get "Port 1313 is not available" even though no server listens on this port.

[christophberger]

As per the docs, using $VAR syntax is valid for environment variables:

version: '3'

env:
  GREETING: Hey, there!

tasks:
  greet:
    cmds:
      - echo $GREETING

[christophberger]

As I cannot reopen this issue, I created #2356. The issue is replicable with an example from the docs.

[vmaerten]

First of all, there are two separate topics here:

• Variable substitution in sh, and
• Variable substitution in msg.

Regarding msg, as far as I know, variables are only replaced through the templating system. I checked back to version 3.40 to confirm this (see attached screenshot):

As for sh, there is indeed a bug, but it’s not related to variable substitution. Since we upgraded the library that runs shell commands from version 3.11 to 3.12, the syntax using ! ... has stopped working.
I need to confirm with them if it's a bug or not. It seems the ! is not taken into account anymore
(See PR: #2319)

You can stay on 3.44.0 meanwhile

[vmaerten]

@andreynering / @pd93, do you think ! nc -z localhost {{.PORT}} should be supported by mvdan/sh ?

[christophberger]

@vmaerten Thanks for the feedback. Curious: Why does msg handle env variable substitution differently than the rest?

 ~/T/taskfile> task --version
3.44.1
 ~/T/taskfile> cat Taskfile.yaml
version: "3"

env:
  FOO: 'foo'
tasks:
  nosubst:
    preconditions:
      - sh: false
        msg: foo is $FOO
  subst:
    cmds:
      - echo foo is $FOO
 ~/T/taskfile> task subst
task: [subst] echo foo is $FOO
foo is foo
 ~/T/taskfile> task nosubst
task: foo is $FOO
task: precondition not met

This is inconsistent and surprising, even more so as my unchanged Taskfile worked fine for a long time.

[vmaerten]

cmd and cmds are different from other fields in Task.
They (along with precondition.sh) are executed through mvdan/sh, which means:

• Shell syntax is parsed and executed.
• Environment variables (like $FOO) are interpolated.

All other fields (like vars, env, preconditions.msg, etc.) are processed using Task’s templating system ({{ .FOO }}), not shell parsing.
So:

• Anything run by mvdan/sh can interpolate environment variables.
• Anything else should use the templating system.

My recommendation: use the templating system ({{ .VAR }}) whenever possible. It's more predictable and portable. Use environment variables only if you specifically need shell behavior.

This is inconsistent and surprising, even more so as my unchanged Taskfile worked fine for a long time.

In which version (excluding the bug with mvdan/sh in v3.41) it worked fine with your taskfile?

I've created an issue in mvdan/sh