Cross(s)hell

A single shell snippet that works in Bash, PowerShell and Command Prompt.

echo ^">NUL \" >$null "'&powershell ";iex (iwr __WINDOWS_SCRIPT_URL__);echo >$null '>/dev/null;curl -s __LINUX_OR_MACOS_SCRIPT_URL__|sh;echo >/dev/null \'

In theory, the script

• on Windows¹ downloads and runs windows_code.ps1.
• on Linux/macOS² downloads and runs linux_or_macos_code.sh.

1. Note there exists a cross-platform PowerShell nowadays, so technically speaking you should still do an OS check there - but realistically speaking, who uses that anyway?

2. ... or any OS that runs a bash-like shell (yeah it could even be Windows through Git Bash or something)

In practice, it works!

sh

PowerShell

Command Prompt

The script

With Bash syntax highlighting

echo ^">NUL \" >$null "'&powershell ";iex (iwr https://raw.githubusercontent.com/kwyntes/crossshell/main/windows_code.ps1);echo >$null '>/dev/null;curl -s https://raw.githubusercontent.com/kwyntes/crossshell/main/linux_or_macos_code.sh|sh;echo >/dev/null \'

With PowerShell syntax highlighting

echo ^">NUL \" >$null "'&powershell ";iex (iwr https://raw.githubusercontent.com/kwyntes/crossshell/main/windows_code.ps1);echo >$null '>/dev/null;curl -s https://raw.githubusercontent.com/kwyntes/crossshell/main/linux_or_macos_code.sh|sh;echo >/dev/null \'

With Batch syntax highlighting

echo ^">NUL \" >$null "'&powershell ";iex (iwr https://raw.githubusercontent.com/kwyntes/crossshell/main/windows_code.ps1);echo >$null '>/dev/null;curl -s https://raw.githubusercontent.com/kwyntes/crossshell/main/linux_or_macos_code.sh|sh;echo >/dev/null \'

Note that the syntax highlighter doesn't actually understand what's going on either.

How does it work?

Short answer: By abusing almost every single syntax feature of each shell.

Long answer: Here's an almost-character-by-character explanation of the whole script:

Character sequence	Bash interpretation	PowerShell interpretation	Command Prompt interpretation
echo	Echo command
^"	Echo ^ and begin doubleq string literal		Echo " (^ is the escape character)
>NUL	<Inside doubleq string literal>		Redirect output to NUL (discard)
\"	"	Echo \ and end doubleq literal	Echo \ and begin string literal3
>$null	"	Redirect output to $null (discard)	<Inside string literal>
"	End doubleq string literal	Begin doubleq string literal	End string literal
'	Begin singleq string literal	<Inside doubleq string literal>	Echo '
&	<Inside singleq string literal>	"	Command seperator
powershell	"	"	Execute powershell ...
"	"	End doubleq string literal	Begin string literal
;	"	Command seperator	Parsed by PowerShell
iex (iwr URL)	"	Download script and execute it	"
;	"	Command seperator	"
echo >$null	"	Echo and redirect to $null	"
'	End singleq string literal	Begin singleq string literal	"
>/dev/null	Redirect output to /dev/null (discard)	<Inside singleq string literal>	"
;	Command seperator	"	"
curl -s URL|sh	Download script and execute it	"	"
;	Command seperator	"	"
echo >/dev/null	Echo and redirect to /dev/null	"	"
\'	Echo '	End singleq string literal	"

3. Command Prompt doesn't seem to behave consistently with string literals so I'm honestly not exactly sure why this works. It also does not feature single-quoted string literals.