String interpolation in PowerShell for hashmaps [duplicate] - string

I have the following code:
$DatabaseSettings = #();
$NewDatabaseSetting = "" | select DatabaseName, DataFile, LogFile, LiveBackupPath;
$NewDatabaseSetting.DatabaseName = "LiveEmployees_PD";
$NewDatabaseSetting.DataFile = "LiveEmployees_PD_Data";
$NewDatabaseSetting.LogFile = "LiveEmployees_PD_Log";
$NewDatabaseSetting.LiveBackupPath = '\\LiveServer\LiveEmployeesBackups';
$DatabaseSettings += $NewDatabaseSetting;
When I try to use one of the properties in a string execute command:
& "$SQlBackupExePath\SQLBackupC.exe" -I $InstanceName -SQL `
"RESTORE DATABASE $DatabaseSettings[0].DatabaseName FROM DISK = '$tempPath\$LatestFullBackupFile' WITH NORECOVERY, REPLACE, MOVE '$DataFileName' TO '$DataFilegroupFolder\$DataFileName.mdf', MOVE '$LogFileName' TO '$LogFilegroupFolder\$LogFileName.ldf'"
It tries to just use the value of $DatabaseSettings rather than the value of $DatabaseSettings[0].DatabaseName, which is not valid.
My workaround is to have it copied into a new variable.
How can I access the object's property directly in a double-quoted string?

When you enclose a variable name in a double-quoted string it will be replaced by that variable's value:
$foo = 2
"$foo"
becomes
"2"
If you don't want that you have to use single quotes:
$foo = 2
'$foo'
However, if you want to access properties, or use indexes on variables in a double-quoted string, you have to enclose that subexpression in $():
$foo = 1,2,3
"$foo[1]" # yields "1 2 3[1]"
"$($foo[1])" # yields "2"
$bar = "abc"
"$bar.Length" # yields "abc.Length"
"$($bar.Length)" # yields "3"
PowerShell only expands variables in those cases, nothing more. To force evaluation of more complex expressions, including indexes, properties or even complete calculations, you have to enclose those in the subexpression operator $( ) which causes the expression inside to be evaluated and embedded in the string.

#Joey has the correct answer, but just to add a bit more as to why you need to force the evaluation with $():
Your example code contains an ambiguity that points to why the makers of PowerShell may have chosen to limit expansion to mere variable references and not support access to properties as well (as an aside: string expansion is done by calling the ToString() method on the object, which can explain some "odd" results).
Your example contained at the very end of the command line:
...\$LogFileName.ldf
If properties of objects were expanded by default, the above would resolve to
...\
since the object referenced by $LogFileName would not have a property called ldf, $null (or an empty string) would be substituted for the variable.

Documentation note: Get-Help about_Quoting_Rules covers string interpolation, but, as of PSv5, not in-depth.
To complement Joey's helpful answer with a pragmatic summary of PowerShell's string expansion (string interpolation in double-quoted strings ("...", a.k.a. expandable strings), including in double-quoted here-strings):
Only references such as $foo, $global:foo (or $script:foo, ...) and $env:PATH (environment variables) can directly be embedded in a "..." string - that is, only the variable reference itself, as a whole is expanded, irrespective of what follows.
E.g., "$HOME.foo" expands to something like C:\Users\jdoe.foo, because the .foo part was interpreted literally - not as a property access.
To disambiguate a variable name from subsequent characters in the string, enclose it in { and }; e.g., ${foo}.
This is especially important if the variable name is followed by a :, as PowerShell would otherwise consider everything between the $ and the : a scope specifier, typically causing the interpolation to fail; e.g., "$HOME: where the heart is." breaks, but "${HOME}: where the heart is." works as intended.
(Alternatively, `-escape the :: "$HOME`: where the heart is.", but that only works if the character following the variable name wouldn't then accidentally form an escape sequence with a preceding `, such as `b - see the conceptual about_Special_Characters help topic).
To treat a $ or a " as a literal, prefix it with escape char. ` (a backtick); e.g.:
"`$HOME's value: $HOME"
For anything else, including using array subscripts and accessing an object variable's properties, you must enclose the expression in $(...), the subexpression operator (e.g., "PS version: $($PSVersionTable.PSVersion)" or "1st el.: $($someArray[0])")
Using $(...) even allows you to embed the output from entire commands in double-quoted strings (e.g., "Today is $((Get-Date).ToString('d')).").
Interpolation results don't necessarily look the same as the default output format (what you'd see if you printed the variable / subexpression directly to the console, for instance, which involves the default formatter; see Get-Help about_format.ps1xml):
Collections, including arrays, are converted to strings by placing a single space between the string representations of the elements (by default; a different separator can be specified by setting preference variable $OFS, though that is rarely seen in practice) E.g., "array: $(#(1, 2, 3))" yields array: 1 2 3
Instances of any other type (including elements of collections that aren't themselves collections) are stringified by either calling the IFormattable.ToString() method with the invariant culture, if the instance's type supports the IFormattable interface[1], or by calling .psobject.ToString(), which in most cases simply invokes the underlying .NET type's .ToString() method[2], which may or may not give a meaningful representation: unless a (non-primitive) type has specifically overridden the .ToString() method, all you'll get is the full type name (e.g., "hashtable: $(#{ key = 'value' })" yields hashtable: System.Collections.Hashtable).
To get the same output as in the console, use a subexpression in which you pipe to Out-String and apply .Trim() to remove any leading and trailing empty lines, if desired; e.g.,
"hashtable:`n$((#{ key = 'value' } | Out-String).Trim())" yields:
hashtable:
Name Value
---- -----
key value
[1] This perhaps surprising behavior means that, for types that support culture-sensitive representations, $obj.ToString() yields a current-culture-appropriate representation, whereas "$obj" (string interpolation) always results in a culture-invariant representation - see this answer.
[2] Notable overrides:
• The previously discussed stringification of collections (space-separated list of elements rather than something like System.Object[]).
• The hashtable-like representation of [pscustomobject] instances (explained here) rather than the empty string.

#Joey has a good answer. There is another way with a more .NET look with a String.Format equivalent, I prefer it when accessing properties on objects:
Things about a car:
$properties = #{ 'color'='red'; 'type'='sedan'; 'package'='fully loaded'; }
Create an object:
$car = New-Object -typename psobject -Property $properties
Interpolate a string:
"The {0} car is a nice {1} that is {2}" -f $car.color, $car.type, $car.package
Outputs:
# The red car is a nice sedan that is fully loaded

If you want to use properties within quotes follow as below. You have to use $ outside of the bracket to print property.
$($variable.property)
Example:
$uninstall= Get-WmiObject -ClassName Win32_Product |
Where-Object {$_.Name -like "Google Chrome"
Output:
IdentifyingNumber : {57CF5E58-9311-303D-9241-8CB73E340963}
Name : Google Chrome
Vendor : Google LLC
Version : 95.0.4638.54
Caption : Google Chrome
If you want only name property then do as below:
"$($uninstall.name) Found and triggered uninstall"
Output:
Google Chrome Found and triggered uninstall

Related

Join three CSV columns and convert them to a formatted email link with Powershell [duplicate]

I have the following code:
$DatabaseSettings = #();
$NewDatabaseSetting = "" | select DatabaseName, DataFile, LogFile, LiveBackupPath;
$NewDatabaseSetting.DatabaseName = "LiveEmployees_PD";
$NewDatabaseSetting.DataFile = "LiveEmployees_PD_Data";
$NewDatabaseSetting.LogFile = "LiveEmployees_PD_Log";
$NewDatabaseSetting.LiveBackupPath = '\\LiveServer\LiveEmployeesBackups';
$DatabaseSettings += $NewDatabaseSetting;
When I try to use one of the properties in a string execute command:
& "$SQlBackupExePath\SQLBackupC.exe" -I $InstanceName -SQL `
"RESTORE DATABASE $DatabaseSettings[0].DatabaseName FROM DISK = '$tempPath\$LatestFullBackupFile' WITH NORECOVERY, REPLACE, MOVE '$DataFileName' TO '$DataFilegroupFolder\$DataFileName.mdf', MOVE '$LogFileName' TO '$LogFilegroupFolder\$LogFileName.ldf'"
It tries to just use the value of $DatabaseSettings rather than the value of $DatabaseSettings[0].DatabaseName, which is not valid.
My workaround is to have it copied into a new variable.
How can I access the object's property directly in a double-quoted string?
When you enclose a variable name in a double-quoted string it will be replaced by that variable's value:
$foo = 2
"$foo"
becomes
"2"
If you don't want that you have to use single quotes:
$foo = 2
'$foo'
However, if you want to access properties, or use indexes on variables in a double-quoted string, you have to enclose that subexpression in $():
$foo = 1,2,3
"$foo[1]" # yields "1 2 3[1]"
"$($foo[1])" # yields "2"
$bar = "abc"
"$bar.Length" # yields "abc.Length"
"$($bar.Length)" # yields "3"
PowerShell only expands variables in those cases, nothing more. To force evaluation of more complex expressions, including indexes, properties or even complete calculations, you have to enclose those in the subexpression operator $( ) which causes the expression inside to be evaluated and embedded in the string.
#Joey has the correct answer, but just to add a bit more as to why you need to force the evaluation with $():
Your example code contains an ambiguity that points to why the makers of PowerShell may have chosen to limit expansion to mere variable references and not support access to properties as well (as an aside: string expansion is done by calling the ToString() method on the object, which can explain some "odd" results).
Your example contained at the very end of the command line:
...\$LogFileName.ldf
If properties of objects were expanded by default, the above would resolve to
...\
since the object referenced by $LogFileName would not have a property called ldf, $null (or an empty string) would be substituted for the variable.
Documentation note: Get-Help about_Quoting_Rules covers string interpolation, but, as of PSv5, not in-depth.
To complement Joey's helpful answer with a pragmatic summary of PowerShell's string expansion (string interpolation in double-quoted strings ("...", a.k.a. expandable strings), including in double-quoted here-strings):
Only references such as $foo, $global:foo (or $script:foo, ...) and $env:PATH (environment variables) can directly be embedded in a "..." string - that is, only the variable reference itself, as a whole is expanded, irrespective of what follows.
E.g., "$HOME.foo" expands to something like C:\Users\jdoe.foo, because the .foo part was interpreted literally - not as a property access.
To disambiguate a variable name from subsequent characters in the string, enclose it in { and }; e.g., ${foo}.
This is especially important if the variable name is followed by a :, as PowerShell would otherwise consider everything between the $ and the : a scope specifier, typically causing the interpolation to fail; e.g., "$HOME: where the heart is." breaks, but "${HOME}: where the heart is." works as intended.
(Alternatively, `-escape the :: "$HOME`: where the heart is.", but that only works if the character following the variable name wouldn't then accidentally form an escape sequence with a preceding `, such as `b - see the conceptual about_Special_Characters help topic).
To treat a $ or a " as a literal, prefix it with escape char. ` (a backtick); e.g.:
"`$HOME's value: $HOME"
For anything else, including using array subscripts and accessing an object variable's properties, you must enclose the expression in $(...), the subexpression operator (e.g., "PS version: $($PSVersionTable.PSVersion)" or "1st el.: $($someArray[0])")
Using $(...) even allows you to embed the output from entire commands in double-quoted strings (e.g., "Today is $((Get-Date).ToString('d')).").
Interpolation results don't necessarily look the same as the default output format (what you'd see if you printed the variable / subexpression directly to the console, for instance, which involves the default formatter; see Get-Help about_format.ps1xml):
Collections, including arrays, are converted to strings by placing a single space between the string representations of the elements (by default; a different separator can be specified by setting preference variable $OFS, though that is rarely seen in practice) E.g., "array: $(#(1, 2, 3))" yields array: 1 2 3
Instances of any other type (including elements of collections that aren't themselves collections) are stringified by either calling the IFormattable.ToString() method with the invariant culture, if the instance's type supports the IFormattable interface[1], or by calling .psobject.ToString(), which in most cases simply invokes the underlying .NET type's .ToString() method[2], which may or may not give a meaningful representation: unless a (non-primitive) type has specifically overridden the .ToString() method, all you'll get is the full type name (e.g., "hashtable: $(#{ key = 'value' })" yields hashtable: System.Collections.Hashtable).
To get the same output as in the console, use a subexpression in which you pipe to Out-String and apply .Trim() to remove any leading and trailing empty lines, if desired; e.g.,
"hashtable:`n$((#{ key = 'value' } | Out-String).Trim())" yields:
hashtable:
Name Value
---- -----
key value
[1] This perhaps surprising behavior means that, for types that support culture-sensitive representations, $obj.ToString() yields a current-culture-appropriate representation, whereas "$obj" (string interpolation) always results in a culture-invariant representation - see this answer.
[2] Notable overrides:
• The previously discussed stringification of collections (space-separated list of elements rather than something like System.Object[]).
• The hashtable-like representation of [pscustomobject] instances (explained here) rather than the empty string.
#Joey has a good answer. There is another way with a more .NET look with a String.Format equivalent, I prefer it when accessing properties on objects:
Things about a car:
$properties = #{ 'color'='red'; 'type'='sedan'; 'package'='fully loaded'; }
Create an object:
$car = New-Object -typename psobject -Property $properties
Interpolate a string:
"The {0} car is a nice {1} that is {2}" -f $car.color, $car.type, $car.package
Outputs:
# The red car is a nice sedan that is fully loaded
If you want to use properties within quotes follow as below. You have to use $ outside of the bracket to print property.
$($variable.property)
Example:
$uninstall= Get-WmiObject -ClassName Win32_Product |
Where-Object {$_.Name -like "Google Chrome"
Output:
IdentifyingNumber : {57CF5E58-9311-303D-9241-8CB73E340963}
Name : Google Chrome
Vendor : Google LLC
Version : 95.0.4638.54
Caption : Google Chrome
If you want only name property then do as below:
"$($uninstall.name) Found and triggered uninstall"
Output:
Google Chrome Found and triggered uninstall

Formatting string in Powershell but only first or specific occurrence of replacement token

I have a regular expression that I use several times in a script, where a single word gets changed but the rest of the expression remains the same. Normally I handle this by just creating a regular expression string with a format like the following example:
# Simple regex looking for exact string match
$regexTemplate = '^{0}$'
# Later on...
$someString = 'hello'
$someString -match ( $regexTemplate -f 'hello' ) # ==> True
However, I've written a more complex expression where I need to insert a variable into the expression template and... well regex syntax and string formatting syntax begin to clash:
$regexTemplate = '(?<=^\w{2}-){0}(?=-\d$)'
$awsRegion = 'us-east-1'
$subRegion = 'east'
$awsRegion -match ( $regexTemplate -f $subRegion ) # ==> Error
Which results in the following error:
InvalidOperation: Error formatting a string: Index (zero based) must be greater than or equal to zero and less than the size of the argument list.
I know what the issue is, it's seeing one of my expression quantifiers as a replacement token. Rather than opt for a string-interpolation approach or replace {0} myself, is there a way I can tell PowerShell/.NET to only replace the 0-indexed token? Or is there another way to achieve the desired output using format strings?
If a string template includes { and/or } characters, you need to double these so they do not interfere with the numbered placeholders.
Try
$regexTemplate = '(?<=^\w{{2}}-){0}(?=-\d$)'

what's the proper way to allow users to provide a string "mangler" as a regex/proc/expr/

In my Tcl/Tk project, i need to allow my users to mangle a string in a well-defined way.
The idea is, to allow people to declare a "string mangling" proc/expr/function/... in a configuration file, which then gets applied to the strings in question.
I'm a bit worried on how to properly implement that.
Possibilities I have considered so far:
regular expressions
That was my first thought, but there's two caveats:
search/replace with regular expressions in Tcl seems to be awkward. at least with regsub i need to pass the match and replacement parts separately (as opposed to how e.g. sed allows me to pass a single complicated string that does everything for me); there are sed implementations for Tcl, but they look naive and might break rather sooner than later
also regexes can be awkward by themselves; using them to mangle complicated strings is often more complicated than it should be
procs?
Since the target platform is Tcl anyhow, why not use the power of Tcl to do string mangling?
The "function" should have a single input and produce a single output, and ideally it the user should be nudged into doing it right (e.g. not being able to define a proc that requires two arguments) and it be (nigh) impossible to create side-effects (like changing the state of the application).
A simplistic approach would be to use proc mymangler s $body (with $body being the string defined by the user), but there are so many things that can go wrong:
$body assuming a different arg-name (e.g. $x instead of $s)
$body not returning anything
$body changing variables,... in the environment
expressions look more like it (always returning things, not allowing to modify the environment easily), but i cannot make them work on strings, and there's no way to pass a variable without agreeing its name.
So, the best I've come up with so far is:
set userfun {return $s} # user-defined string
proc mymangler s ${userfun}
set output [mymangler $input]
Are there better ways to achieve user-defined string-manglers in Tcl?
You can use apply -- the user provides a 2-element list: the second element is the "proc body", the code that does the mangling; the first element is the variable name to hold the string, this variable is used in the body.
For example:
set userfun {{str} {string reverse $str}}
set input "some string"
set result [apply $userfun $input] ;# => "gnirts emos"
Of course the code you get from the user is any arbitrary Tcl code. You can run it in a safe interpreter:
set userfun {{str} {exec some malicious code; return [string reverse $str]}}
try {
set interp [safe::interpCreate]
set result [$interp eval [list apply $userfun $input]]
puts "mangled string is: $result"
safe::interpDelete $interp
} on error e {
error "Error: $e"
}
results in
Error: invalid command name "exec"
Notes:
a standard Tcl command is used, apply
the user must specify the variable name used in the body.
this scheme does protect the environment:
set userfun {{str} {set ::env(SOME_VAR) "safe slave"; return $str$str}}
set env(SOME_VAR) "main"
puts $env(SOME_VAR)
try {
set interp [safe::interpCreate]
set result [$interp eval [list apply $userfun $input]]
puts "mangled string is: $result"
safe::interpDelete $interp
} on error e {
error "Error: $e"
}
puts $env(SOME_VAR)
outputs
main
mangled string is: some stringsome string
main
if the user does not return a value, then the mangled string is simply the empty string.
The "simplistic" approach is like foreach in that it requires the user to supply a variable name and a script to evaluate that uses that variable, and is a good approach. If you don't want it affecting the rest of the program, run it in a separate interpreter:
set x 0
proc mymangler {name body} {
set i [interp create -safe]
set s "some string to change"
try {
# Build the lambda used by apply here instead of making
# the user do it.
$i eval [list apply [list $name $body] $s]
} on error e {
return $e
} finally {
interp delete $i
}
}
puts [mymangler s { set x 1; string toupper $s }]
puts $x
outputs
SOME STRING TO CHANGE
0
If the person calling this says to use s as a variable and then uses something else in the body, it's on them. Same with providing a script that doesn't return anything.
I'd generally allow the user to specify a command prefix as a Tcl list (most simple command names are trivially suitable for this), which you would then apply to the argument by doing:
set mangled [{*}$commandPrefix $valueToMangle]
This lets people provide pretty much anything they want, especially as they can use apply and a lambda term to mangle things as required. Of course, if you're in a procedure then you're probably actually better off doing:
set mangled [uplevel 1 [list {*}$commandPrefix $valueToMangle]]
so that you're running in the caller's context (change 1 to #0 to use the global context instead) which can help protect your procedure against accidental changes and make using upvar within the mangler easier.
If the source of the mangling prefix is untrusted (what that means depends greatly on your application and deployment) then you can run the mangling code in a separate interpreter:
# Make the safe evaluation context; this is *expensive*
set context [interp create -safe]
# You might want to let them define extra procedures too
# interp invokehidden $context source /the/users/file.tcl
# Use the context
try {
set mangled [interp eval $context [list {*}$commandPrefix $valueToMangle]]
} on error {msg} {
# User supplied something bad; error message in $msg
}
There's various ways to support users specifying the transformation, but if you can expose the fact that you're working with Tcl to them then that's probably easiest and most flexible.

Replacing a certain part of string with a pre-specified Value

I am fairly new to Puppet and Ruby. Most likely this question has been asked before but I am not able to find any relevant information.
In my puppet code I will have a string variable retrieved from the fact hostname.
$n="$facts['hostname'].ex-ample.com"
I am expecting to get the values like these
DEV-123456-02B.ex-ample.com,
SCC-123456-02A.ex-ample.com,
DEV-123456-03B.ex-ample.com,
SCC-999999-04A.ex-ample.com
I want to perform the following action. Change the string to lowercase and then replace the
-02, -03 or -04 to -01.
So my output would be like
dev-123456-01b.ex-ample.com,
scc-123456-01a.ex-ample.com,
dev-123456-01b.ex-ample.com,
scc-999999-01a.ex-ample.com
I figured I would need to use .downcase on $n to make everything lowercase. But I am not sure how to replace the digits. I was thinking of .gsub or split but not sure how. I would prefer to make this happen in a oneline code.
If you really want a one-liner, you could run this against each string:
str
.downcase
.split('-')
.map
.with_index { |substr, i| i == 2 ? substr.gsub(/0[0-9]/, '01') : substr }
.join('-')
Without knowing what format your input list is taking, I'm not sure how to advise on how to iterate through it, but maybe you have that covered already. Hope it helps.
Note that Puppet and Ruby are entirely different languages and the other answers are for Ruby and won't work in Puppet.
What you need is:
$h = downcase(regsubst($facts['hostname'], '..(.)$', '01\1'))
$n = "${h}.ex-ample.com"
notice($n)
Note:
The downcase and regsubst functions come from stdlib.
I do a regex search and replace using the regsubst function and replace ..(.)$ - 2 characters followed by another one that I capture at the end of the string and replace that with 01 and the captured string.
All of that is then downcased.
If the -01--04 part is always on the same string index you could use that to replace the content.
original = 'DEV-123456-02B.ex-ample.com'
# 11 -^
string = original.downcase # creates a new downcased string
string[11, 2] = '01' # replace from index 11, 2 characters
string #=> "dev-123456-01b.ex-ample.com"

How do I replace a numeric part of a string by another number in Tcl?

I have a string in a format similar to 1005-abcd and I want to replace the numeric part of this string by another number and make it like 1008-abcd.
I can achieve this by using the following -
string map {1005 1008} "1005-abcd"
But I have these numbers in form of variables. For example, $source is 1005 and $new is 1008. When I use the same command like this -
string map {$source $new} "1005-abcd"
Braces prevent substitution of the variables. Use another way to give the list and enable substitution. One option:
string map "$source $new" "1005-abcd"
Another (better) option:
string map [list $source $new] "1005-abcd"

Resources