A PowerShell Solution

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PowerShell is the #33 most used language in Github as of 2022 Q1 according to GitHut’s statistics. Let’s take a look at what this scripting language can do.

Code

3 alphanumericals chosen: i, e and x.

$i=$?+$?
$e=$i+$i
$xi=$x=$e+$i
$xe=""+$x+$x
$xx=""+$x+--$e
$x=(""+$?)[$i]
iex "`$ex=""``$x{$xe}"";`$xe=""``$x{$xx}"""
$ii=$e+++$i
$ix=$ii+$i
$ei=$e*$i
$x="``$x{"
iex "`$e=""$x$e$ei}e$x$xi$xe}$x$xi$xe}$x$xi$ex}, $x$ii$ix}$x$xi$ex}$x$ix$i}$x$xi$xe}$x$xi$e}!"""
$e

Semicolons are necessary if the code is written in a single line. The two are equivalent.

$i=$?+$?;$e=$i+$i;$xi=$x=$e+$i;$xe=""+$x+$x;$xx=""+$x+--$e;$x=(""+$?)[$i];iex "`$ex=""``$x{$xe}"";`$xe=""``$x{$xx}""";$ii=$e+++$i;$ix=$ii+$i;$ei=$e*$i;$x="``$x{";iex "`$e=""$x$e$ei}e$x$xi$xe}$x$xi$xe}$x$xi$ex}, $x$ii$ix}$x$xi$ex}$x$ix$i}$x$xi$xe}$x$xi$e}!""";$e

Environment

PowerShell 7.2.5

Please install it manually. Since the code uses the "`u{x}" syntax which was added in PowerShell 6.0, it won’t work on the one preinstalled on Windows.

The code can be run by either pasting it into the PowerShell console or using .\x.ps1.

Explanation

My first thought was if it is possible to directly add or subtract the ASCII value of chars like in most C-style language. However, this is not possible. The target type must be written when it comes to explicit type conversion. [char]65 does give us the character A, but there are 4 different letters. And if we want to get a number, it’s [int] something. ^[1].

Selection of the 3 characters

Then I try to find the eval function. First I found the very one Invoke-Expression, but that is too long. Most PowerShell commands are long. That’s bad for a scripting language. Then I found that the ampersand, &, can execute command in a string. But it works on a single command, without parameters.^[2] Luckily, there is an alias of Invoke-Expression: iex.

The first digit

Since there is no way to turn a single char into another, the only way to get a 4th character is to split a String elsewhere. In PowerShell, a character quoted by either '' or " is always a string, an array of chars. There is no .pop() in Powershell,^[3] so we need to access it by index if we want a specific character.

$i = $? + $?

$? contains the execution status of the last command. It is True initially or when the last command succeeded.^[4]
The equivalent of == is -eq in Powershell; $i==$i won’t work.
True is 1 when casted to an integer.^[5]
Most lines of code are aimed at getting the digits needed. There is still much room for optimization.

Composing Unicode characters

$x = ("" + $?)[$i]

An empty string plus a boolean turns into a string.

Thanks to the u in "True", we can compose any Unicode character now. The hex for hello world string contains c and f. Just get the two first. The $e variable is actually:

$e = "``u{48}e``u{6c}``u{6c}``u{6f}, ``u{57}``u{6f}``u{72}``u{6c}``u{64}!";

Escaping

iex "`$ex=""``$x{$xe}"";`$xe=""``$x{$xx}"""

To escape , `$, ", just add ` in front of them or repeat the character itself.^[6]

Printing the result

PowerShell prints out the value of the previous expression by default, so there is no need to iex "echo" something.

Other possible approaches

The output of a command can be assigned to a variable. Maybe we can find all the needed characters in some commands' default output.
$error stores previous error messages and requires 3 characters.