René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Preventing setting 'Ignore' as the $ErrorActionPreference value is poorly enforced on the command line, and not at all in scripts","articleBody":"\u003csup\u003eRelated: #1759\u003c/sup\u003e\r\n\r\nThe `Ignore` error-action value is meant to be used only with the `-ErrorAction` _common parameter_, not with the `$ErrorActionPreference` _preference variable_.\r\n\r\nAn explicit check to prevent the latter was clearly implemented (as evidenced by error message `The value Ignore is not supported for an ActionPreference variable. The provided value should be used only as a \r\nvalue for a preference parameter, and has been replaced by the default value.`), but it doesn't / doesn't properly take effect.\r\n\r\n* On the **command line**, `$ErrorActionPreference = 'Ignore'` is **accepted _at first_**. When the next error occurs, it is the error message about the invalid `$ErrorActionPreference` value that surfaces instead of the actual error's, and _only at that point_ is `$ErrorActionPreference` **reset to `Continue`**.\r\n\r\n* In a **script**, `$ErrorActionPreference = 'Ignore'` is **accepted _and_ takes effect**. A contributing factor is that **preference variables in child scopes are not type-constrained,** so I presume that no validation takes place at assignment time - see #3483\r\n\r\n\r\nSteps to reproduce\r\n------------------\r\n\r\n* On the command line:\r\n\r\n```powershell\r\n# On the command line: set to invalid value, reflect it, then trigger an error, then reflect it again.\r\n\u003e $ErrorActionPreference = 'Ignore'; $ErrorActionPreference; 1 / 0; $ErrorActionPreference\r\n```\r\n\r\n* In a script (place code in a `*.ps1` file):\r\n\r\n```powershell\r\n$ErrorActionPreference = 'Ignore'; $ErrorActionPreference; 1/0; $ErrorActionPreference\r\n```\r\n\r\nExpected behavior\r\n-----------------\r\n\r\n* Both on the command line and in a script:\r\n\r\n```none\r\nThe value Ignore is not supported for an ActionPreference variable. The provided value should be used only as a \r\nvalue for a preference parameter, and has been replaced by the default value.\r\n...\r\nContinue\r\nAttempted to divide by zero.\r\n...\r\nContinue\r\n```\r\n\r\nActual behavior\r\n---------------\r\n\r\n* On the command line:\r\n\r\n```none\r\nIgnore\r\n$ErrorActionPreference = 'Ignore'; $ErrorActionPreference; 1 / 0: The value Ignore is not supported for an ActionPreference variable. The provided value should be used \r\nonly as a value for a preference parameter, and has been replaced by the default value. For more information, see the Help topic, \"about_Preference_Variables.\"\r\n    + CategoryInfo          : NotSpecified: (:) [], NotSupportedException\r\n    + FullyQualifiedErrorId : System.NotSupportedException\r\nContinue\r\n```\r\n\r\nThe value was accepted at first and retained until the next error occurred. The next error's message is mistakenly replaced with the invalid-$ErrorActionPreference-value error message, and the value is reset to `Continue` at that point.\r\n\r\n* In a script:\r\n\r\n```none\r\nIgnore\r\nIgnore\r\n```\r\n\r\nThe value was accepted, stayed in effect, and suppressed the statement-terminating error.\r\n\r\nEnvironment data\r\n----------------\r\n\r\n```powershell\r\nPowerShell Core v6.0.0-beta.4 on macOS 10.12.5\r\nPowerShell Core v6.0.0-beta.4 on Ubuntu 16.04.2 LTS\r\nPowerShell Core v6.0.0-beta.4 on Microsoft Windows 10 Pro (64-bit; v10.0.15063)\r\nWindows PowerShell v5.1.15063.413 on Microsoft Windows 10 Pro (64-bit; v10.0.15063)\r\n```\r\n","author":{"url":"https://github.com/mklement0","@type":"Person","name":"mklement0"},"datePublished":"2017-07-26T16:15:06.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":15},"url":"https://github.com/4348/PowerShell/issues/4348"}