While I am using Write-Verbose in powershell command window I'm not getting anything in the console. However it is used by devops engineers in my team for continuous integration, build scripts.
What is the difference between Write-Verbose and Write-Host
The difference between the cmdlets (as of powershell-v5.0) is which stream they use to display information. By default, the Verbose stream (4) is not visible unless you specify -Verbose, add -Verbose using the $PSDefaultParameterValues automatic dictionary to append the switch to all or specific cmdlets, or setting the $VerbosePreference automatic variable.
You can observe this stream behavior as such:
PS ~/> Write-Verbose -Message 'Just testing' -Verbose 4>$null
PS ~/> Write-Verbose -Message 'Just testing' -Verbose
VERBOSE: Just testing
Likewise, the Write-Host cmdlet uses the Information stream (6) which is also not visible by default, but Write-Host essentially became a wrapper for
Write-Information -InformationAction Continue
This stream has the same requirements as the Verbose stream to be seen with the preference variable being $InformationPreference.
You can additionally observe these objects by assigning their output:
PS ~/> $output = Write-Verbose -Message test -Verbose 4>&1
PS ~/> $output | Get-Member
TypeName: System.Management.Automation.VerboseRecord
Name MemberType Definition
---- ---------- ----------
Equals Method bool Equals(System.Object obj)
GetHashCode Method int GetHashCode()
GetType Method type GetType()
ToString Method string ToString()
WriteVerboseStream NoteProperty bool WriteVerboseStream=True
InvocationInfo Property System.Management.Automation.InvocationInfo InvocationInfo {get;}
Message Property string Message {get;set;}
PipelineIterationInfo Property System.Collections.ObjectModel.ReadOnlyCollection[int] PipelineIterationInfo
PS ~/> $output = Write-Host -Object test 6>&1
PS ~/> $output | Get-Member
TypeName: System.Management.Automation.InformationRecord
Name MemberType Definition
---- ---------- ----------
Equals Method bool Equals(System.Object obj)
GetHashCode Method int GetHashCode()
GetType Method type GetType()
ToString Method string ToString()
WriteInformationStream NoteProperty bool WriteInformationStream=True
Computer Property string Computer {get;set;}
ManagedThreadId Property uint ManagedThreadId {get;set;}
MessageData Property System.Object MessageData {get;}
NativeThreadId Property uint NativeThreadId {get;set;}
ProcessId Property uint ProcessId {get;set;}
Source Property string Source {get;set;}
Tags Property System.Collections.Generic.List[string] Tags {get;}
TimeGenerated Property datetime TimeGenerated {get;set;}
User Property string User {get;set;}
Valid values for the preference variables are as such:
[System.Management.Automation.ActionPreference].GetEnumValues()
about_Redirection
Write-Verbose Write to console only when the -Verbose Parameters is used.
Write-Host Write to the console anyway...
You need to add the [CmdletBinding()] to the file before the Param Section to enable the -Verbose Parameter...
See Example:
[CmdletBinding()]
Param(
)
Write-Verbose "Verbose"
Write-Host "Host"
PS C:\> .\test.ps1
Host
PS C:\> .\test.ps1 -Verbose
VERBOSE: Verbose
Host
Looking at the definitions
Write-Verbose Writes text to the verbose message stream.
Write-Host Writes customized output to a host.
I think your devops engineers would have set $VerbosePreference = "Continue" before running their scripts due to which the Verbose logs also output to the console.
Let's see an example
PS > Write-Verbose "hello"
> NO OUTPUT
PS > Write-Host "hello"
hello
PS > $VerbosePreference = "Continue"
PS > Write-Verbose "hello"
VERBOSE: hello
The important thing to remember is that cmdlets like Write-Verbose, Write-Error etc. are for providing different levels of logging i.e. it is useful when you are monitoring the logs and want to filter by log-level. This answers questions like "How many errors did we get?"(Write-Error), "Is this function being called?" (Write-Debug)
In contrast, Write-Host could typically be for showing "Output" to the user on the progress of the cmdlet, asking for input etc.
References:
Write-Verbose is only "active" when the -Verbose switch is passed to the cmdlet - otherwise, the assumption is that you don't want to see the messages that would otherwise be generated.
Write-Host outputs its data unconditionally, and bypasses the PowerShell pipeline.
