Powershell tab expansion functions take 2 parameters, the line so far, and the "current word". The function should return a replacement for the current word.
From experiment, it seems to me that the current word is passed to the function without any quotes, and the returned word is inserted into the line with the same quoting as the original. So, for example, if I type
PS> foo "bar"<TAB>
I will get the string bar passed to my tab expansion function (without quotes), and my returned value will be placed back on the line in double quotes.
This behaviour causes problems in certain cases. For example, partial completion of file names, where I might type C:\Pro<TAB> to get "C:\Program Files", but I then need to delete the final quote to expand further (say, by typing \Micro and then hitting TAB again.
Also, returning an expanded value containing quotes can be very messy:
PS> function TabExpansion($line, $lastword) {
PS> "looks like '" + $lastword + "' when quoted"
PS> }
PS>
PS> Silly 'example'<TAB>
This results in unbalanced quotes.
Is there any way of avoiding or working around this behaviour?
Paul.
First off, this is not true:
This behaviour causes problems in
certain cases. For example, partial
completion of file names, where I
might type C:\Pro to get
"C:\Program Files", but I then need to
delete the final quote to expand
further (say, by typing \Micro and
then hitting TAB again.
You can continue typing the \Micro after the quote and it will take care of it for you.
If you really need to return a value containing quotes, you can inject the escape character (`) into your string. Note that you will need to escape the escape character itself so it doesn't get eaten:
function TabExpansion($line, $lastword){
"looks like ``'" + $lastword + "``' when quoted"
}
After Tab expansion, your example will look like:
Silly "looks like `'example`' when quoted"
and the parser should have no problem with it.
Related
I'm trying to make a GUI that will print the information from a textbox into a .txt in a way that I will try to explain as well as I can.
$TextBox_UsbName.text = "TestingTesting"
$Button_SetUsbName.Add_Click({ $Value_UsbName = $TextBox_UsbName.text; add-content -path $Value_NewScriptPath -value "$usbname = $Value_UsbName" })
After this is run I was hoping the text file would contain this:
$usbname = "TestingTesting"
I am still new to Powershell as well as coding in general and now I am really stuck I have tried a lot of different ways.
Any ideas and help would be much appreciated.
Edit: My result is
=
In Powershell double quoted string literals, string interpolation takes place each time an unescaped $ appears with a valid identifier characters after it. To introduce a literal $ that should not be parsed as part of an interpolated variable, you should escape it with a backtick, `.
Here is some quick string interpolation help:
How do I expand an expression in a string?
Windows PowerShell will expand a variable or an expression in a string.
Variables look like: $variable
Expressions look like: $(expression)
So, your "$usbname = $Value_UsbName" is interpreted by the engine as value of $usbname variable followded with = enclosed with spaces, and then a value of $Value_UsbName variable.
What you want to add is a literal $usbname substring and the value of $TextBox_UsbName.text expression.
So, either use
"`$usbname = $($TextBox_UsbName.text)"
Or just concatenate values (in a culture independent way):
$usbname + ' = ' + $TextBox_UsbName.text
I have a line saved as $variable1, for example:
file"yourtxthere/i/master.ext" autostart:true, width
How would I go about writing the correct syntax using Regex in Powershell to grab everything within the quotes. Are regular expressions the best way to do this in Powershell?
Though regular expressions are powerful, this is a simple case. Thus a simple solution is based on string object's split() method.
$variable1 = 'file"yourtxthere/i/master.ext" autostart:true, width'
# Splitting requires at least one "
if ($variable1.IndexOf('"') -gt 0) {
$variable1.Split('"')[1]
}
Splitting the string will result an array of three elements:
file
yourtxthere/i/master.ext
autostart:true, width
As Powershell's arrays begin with index zero, the desired data is at index location 1. In case the string doesn't contain a double quote, the split won't work. This is checked with the statement
if ($variable1.IndexOf('"') -gt 0)
Without one, splitting a quoteless string would return just a one-celled array and trying to access index 1 would result in an error message:
$variable1.Split('!')[1]
Index was outside the bounds of the array.
I'm not 100% sure I understand the question but assuming you had that stored in $variable1 as a string like so:
$variable1 = 'file"yourtxthere/i/master.ext" autostart:true, width'
Then you could extract just the quoted text by splitting the string using the double quotes as a delimiter like this:
$variable1.Split('"')[1]
That splits the string into an array with three parts. The first part is everything before the first double quotes and the second everything in between the first and second quote marks, and the third everything after the second quotation marks. The [1] tells it to output the second part.
I think this picture might illustrate it a little better.
There are other ways to split that up and in fact the variable isn't necessary at all if you do something like this:
('file"yourtxthere/i/master.ext" autostart:true, width').split('"')[1]
That will work fine so long as there are never any extra double quotes before the first occurrence.
Note: A summary of this question has since been posted at the PowerShell GitHub repository, since superseded by this more comprehensive issue.
Arguments passed to a command in PowerShell are parsed in argument mode (as opposed to expression mode - see Get-Help about_Parsing).
Conveniently, (double-)quoting arguments that do not contain whitespace or metacharacters is usually optional, even when these arguments involve variable references (e.g. $HOME\sub) or subexpressions (e.g., version=$($PsVersionTable.PsVersion).
For the most part, such unquoted arguments are treated as if they were double-quoted strings, and the usual string-interpolation rules apply (except that metacharacters such as , need escaping).
I've tried to summarize the parsing rules for unquoted tokens in argument mode in this answer, but there are curious edge cases:
Specifically (as of Windows PowerShell v5.1), why is the unquoted argument token in each of the following commands NOT recognized as a single, expandable string, and results in 2 arguments getting passed (with the variable reference / subexpression retaining its type)?
$(...) at the start of a token:
Write-Output $(Get-Date)/today # -> 2 arguments: [datetime] obj. and string '/today'
Note that the following work as expected:
Write-Output $HOME/sub - simple var. reference at the start
Write-Output today/$(Get-Date) - subexpression not at the start
.$ at the start of a token:
Write-Output .$HOME # -> 2 arguments: string '.' and value of $HOME
Note that the following work as expected:
Write-Output /$HOME - different initial char. preceding $
Write-Output .-$HOME - initial . not directly followed by $
Write-Output a.$HOME - . is not the initial char.
As an aside: As of PowerShell Core v6.0.0-alpha.15, a = following a simple var. reference at the start of a token also seems to break the token into 2 arguments, which does not happen in Windows PowerShell v5.1; e.g., Write-Output $HOME=dir.
Note:
I'm primarily looking for a design rationale for the described behavior, or, as the case may be, confirmation that it is a bug. If it's not a bug, I want something to help me conceptualize the behavior, so I can remember it and avoid its pitfalls.
All these edge cases can be avoided with explicit double-quoting, which, given the non-obvious behavior above, may be the safest choice to use routinely.
Optional reading: The state of the documentation and design musings
As of this writing, the v5.1 Get-Help about_Parsing page:
incompletely describes the rules
uses terms that aren't neither defined in the topic nor generally in common use in the world of PowerShell ("expandable string", "value expression" - though one can guess their meaning)
From the linked page (emphasis added):
In argument mode, each value is treated as an expandable string unless it begins with one of the following special characters: dollar sign ($), at sign (#), single quotation mark ('), double quotation mark ("), or an opening parenthesis (().
If preceded by one of these characters, the value is treated as a value expression.
As an aside: A token that starts with " is, of course, by definition, also an expandable string (interpolating string).
Curiously, the conceptual help topic about quoting, Get-Help about_Quoting_Rules, manages to avoid both the terms "expand" and "interpolate".
Note how the passage does not state what happens when (non-meta)characters directly follow a token that starts with these special characters, notably $.
However, the page contains an example that shows that a token that starts with a variable reference is interpreted as an expandable string too:
With $a containing 4, Write-Output $a/H evaluates to (single string argument) 4/H.
Note that the passage does imply that variable references / subexpressions in the interior of an unquoted token (that doesn't start with a special char.) are expanded as if inside a double-quoted string ("treated as an expandable string").
If these work:
$a = 4
Write-Output $a/H # -> '4/H'
Write-Output H/$a # -> 'H/4'
Write-Output H/$(2 + 2) # -> 'H/4'
why shouldn't Write-Output $(2 + 2)/H expand to '4/H' too (instead of being treated as 2 arguments?
Why is a subexpression at the start treated differently than a variable reference?
Such subtle distinctions are hard to remember, especially in the absence of a justification.
A rule that would make more sense to me is to unconditionally treat a token that starts with $ and has additional characters following the variable reference / subexpression as an expandable string as well.
(By contrast, it makes sense for a standalone variable reference / subexpression to retain its type, as it does now.)
Note that the case of a token that starts with .$ getting split into 2 arguments is not covered in the help topic at all.
Even more optional reading: following a token that starts with one of the other special characters with additional characters.
Among the other special token-starting characters, the following unconditionally treat any characters that follow the end of the construct as a separate argument (which makes sense):
( ' "
Write-Output (2 + 2)/H # -> 2 arguments: 4 and '/H'
Write-Output "2 + $a"/H # -> 2 arguments: '2 + 4' and '/H', assuming $a equals 4
Write-Output '2 + 2'/H # -> 2 arguments: '2 + 2' and '/H'
As an aside: This shows that bash-style string concatenation - placing any mix of quoted and unquoted tokens right next to each other - is not generally supported in PowerShell; it only works if the 1st substring / variable reference happens to be unquoted. E.g., Write-Output H/'2 + 2', unlike the substrings-reversed example above, produces only a single argument.
The exception is #: while # does have special meaning (see Get-Help about_Splatting) when followed by just a syntactically valid variable name (e.g., #parms), anything else causes the token to be treated as an expandable string again:
Write-Output #parms # splatting (results in no arguments if $parms is undefined)
Write-Output #parms$a # *expandable string*: '#parms4', if $a equals 4
I think what you're sort of hitting here is more the the type "hinting" than anything else.
You're using Write-Output which specifies in it's Synopsis that it
Sends the specified objects to the next command in the pipeline.
This command is designed to take in an array. When it hits the first item as a string like today/ it treats it like a string. When the first item ends up being the result of a function call, that may or may not be a string, so it starts up an array.
It's telling that if you run the same command to Write-Host (which is designed to take in a string to output) it works as you'd expect it to:
Write-Host $(Get-Date)/today
Outputs
7/25/2018 1:30:43 PM /today
So I think you're edge cases you're running up against are less about the parsing, and mor about the typing that powershell uses (and tries to hide).
I'm trying to execute a .VB script along with some other arguments.
I'm calling system("$cmd"), where
my $cmd = "Report.exe $app_env $rpt_Dir $eff_date";
and
my $rpt_Dir = "\\\\server\\folder\\Target Report\\test";
The problem I am having is that (I think) the space between "Target Report" is making the script treating it as 2 arguments.
And the reason why I didn't just surround the path with "" and pass it as an argument instead of saving it to a variable is that the path changes based on the date.
And it's not a first choice that I change the code in the .VB script.
On Windows, the system call uses cmd.exe to process commands, so you need double quotes around any parameters that contain spaces
Set your $cmd up like this
my $cmd = qq{Report.exe $app_env "$rpt_Dir" $eff_date};
The qq{...} construction is identical to ordinary double quotes, but it allows you to choose your own delimiters so that you don't have to escape any embedded double quotes
Then you can write
system($cmd);
It is wrong to put quotes around a solitary scalar variable
You can pass an array of args to system. If you do this, you won't be tripped over by quote interpolation.
system ( "Report.exe", $app_env, $rpt_Dir, $eff_date );
You can simply enclose the $rpt_Dir variable in single quotes:
my $cmd = "Report.exe $app_env '$rpt_Dir' $eff_date";
and it will be treated as a single arguement
Please could anyone explain me why the following happens:
"Fancy string - Hor""ray"
# outputs correctly (only one double quote): Fancy string - Hor"ray
'Hor"ray'.Replace('"', '""')
# outputs correctly (two double quotes): Hor""ray
"Fancy string - $('Hor"ray'.Replace('"', '"'+'"'))"
#outputs correctly (two double quotes): Hor""ray
"Fancy string - $('Hor"ray'.Replace('"', '""'))"
# outputs INCORRECTLY (only one double quote): Fancy string - Hor"ray
In my opinion, developers would intuitively expect, that within "$(inline expressions)" Powershell would treat text as statements and won't interfere with the last argument of Replace('"', '""') converting it into '"' (unless the statement interpreter decides to do so).
Do I miss something here?
This appears to be a bug in how PowerShell parses expandable string literals.
From ยง2.3.5.2 on string literals in the PowerShell 3.0 Language Specification, the expandable-string-literal explicitly rejects the $( sequence so that sub-expression parsing will occur instead.
So it seems reasonable to expect $('""') to parse consistently, whether or not it happens to be embedded in a string literal. And clearly sub-expressions are parsed separately, since they support values that would be illegal on their own in an expandable string (e.g. you can write "$('"')" or "$('`""')", where " '"' " or " '`""' " would fail).
However, comparing the AST from [Management.Automation.Language.Parser]::ParseInput for both $('""') and "$('""')", we get two different results. Both have a final StringConstantExpressionAst element with an Extent of '""', but the Value for the stand-alone sub-expression is "" while the Value for the embedded sub-expression is ".
Its because the inline expression is evaluated and its string value is then placed in the string and evaluated.
#Breaking "Fancy string - $('Hor"ray'.Replace('"', '""'))" down
#This inline expression is evaluated first
$('Hor"ray'.Replace('"', '""'))
#giving
Hor""ray
#That value is then interpreted as part of the string
"Fancy string - Hor""ray"
#giving
Fancy string - Hor"ray
This is exactly what I would expect to see. The inline expression evaluated and its resulting value then being used.
Could this not be done by simply using things like below:
`'$($RemFiles[$i].FullName)`'
`"$($RemFiles[$i].FullName)`"
Use the backtick and either a single or double quote to then prevent powershell from using this as an open comment, thus putting the actual symbol in...
The above outputs:
'F:\portable\adobe'
or
"F:\portable\adobe"
I noticed that it seems you are telling it to literally add two double quotes rather than just using the backtick to force it. Therefore telling it to add nothing surely :S So could you change this to something like this:
"Fancy string - $('Hor"ray'.Replace('"', '`"`"'))"
Though that may make 3, as you have one present in Hor"ray anyway.
Just got to test it, was busy with something:
PS D:\> "Fancy string - $('Hor"ray'.Replace('"', '`"`"'))"
Fancy string - Hor""ray
Scroll down on the site below to find out about the backtick and how/where it can be used.
http://www.neolisk.com/techblog/powershell-specialcharactersandtokens