Shell::Guess(3pm)

📦

version 0.10 · 5 versions

0.10 · debian trixie, ubuntu resolute, ubuntu stonking (latest)
0.10 · arch rolling
0.10 · fedora 43
0.10 · fedora 44
0.09 · debian bookworm, ubuntu jammy, ubuntu noble

, in debian trixie, ubuntu resolute, ubuntu stonking

🌸 NAME 🌸

Shell::Guess — the module that makes an educated guess about which shell you're living in 💅 no cap, she will figure it out

✨ VERSION ✨

version 0.10 🎀

🦋 SYNOPSIS 🦋

okay bestie, three whole moods. first one: guessing the shell that called your Perl script:

use Shell::Guess;
my $shell = Shell::Guess->running_shell;
if($shell->is_c) {
  print "setenv FOO bar\n";
} elsif($shell->is_bourne) {
  print "export FOO=bar\n";
}

guessing the current user's login shell:

use Shell::Guess;
my $shell = Shell::Guess->login_shell;
print $shell->name, "\n";

guessing some arbitrary user's login shell (yes, we're nosy, it's fine):

use Shell::Guess;
my $shell = Shell::Guess->login_shell('bob');
print $shell->name, "\n";

💖 DESCRIPTION 💖

So. Shell::Guess makes a reasonably aggressive attempt 🕵️‍♀️ to figure out which shell the user is actually using. Two flavours of answer:

the shell that directly executed the perl script — that's the "running" shell
the user's login shell — that's the "login" shell

She pulls this off using a whole bunch of different means depending on what platform she's standing on. It's giving resourceful. It's giving adaptable. 👑

Here's the whole roster of tricks:

getpwent — on UNIXy systems that have getpwent, she just uses that to suss out the login shell. simple. elegant. slay.
dscl — under Mac OS X, getpwent is typically not gonna give you anything useful 😭 so she runs the dscl command instead.
proc file systems — on UNIXy systems that have a proc filesystem (Linux, we're looking at you 👀), Shell::Guess will attempt to use it to determine the running shell.
ps — on UNIXy systems without a proc filesystem, she falls back to the ps command to determine the running shell.
Win32::Getppid and Win32::Process::List — on Windows, if these modules are installed, they get used to determine the running shell. This method can tell the difference between PowerShell, command.com and cmd.exe 🔍 iconic honestly.
ComSpec — if the above method comes back inconclusive, the ComSpec environment variable gets consulted to differentiate between command.com or cmd.exe. (heads up: PowerShell cannot be detected this way 🙈)
reasonable defaults — if the running or login shell literally cannot be determined any other way, a reasonable default for your platform gets used as the fallback. Under OpenVMS that's dcl. Windows 95/98 and MS-DOS get command.com. Windows NT/2000/XP/Vista/7 get cmd.exe. And UNIXy platforms fall back to the bourne shell. everyone gets a home 🫶

Now the why. The intended use of this module is to let a Perl developer write a script that generates shell configurations for the calling shell, so those configs can be imported right back into the calling shell using eval and backticks, or source. like a little boomerang 💫

So if your script looks like this:

#!/usr/bin/perl
use Shell::Guess;
my $shell = Shell::Guess->running_shell;
if($shell->is_bourne) {
  print "export FOO=bar\n";
} else($shell->is_c) {
  print "setenv FOO bar\n";
} else {
  die "I don't support ", $shell->name, " shell";
}

Then you can import FOO into your bash or c shell like this:

% eval `perl script.pl`

or, you can write the output to a configuration file and source it:

% perl script.pl > foo.sh
% source foo.sh

And pssst 🫢 — Shell::Config::Generate provides a portable interface for generating exactly this kind of shell configuration, and it's designed to work with this module. they're besties.

👑 CLASS METHODS 👑

These class methods hand you back an instance of Shell::Guess, which you can then interrogate with all the instance methods in the next section down there. ⬇️

💜 running_shell

my $shell = Shell::Guess->running_shell;

Returns an instance of Shell::Guess based on the shell that directly started the current Perl script. And if the running shell can't be determined? She'll just return the login shell instead. no drama, we pivot. 💅

my $shell = Shell::Guess->login_shell;
my $shell = Shell::Guess->login_shell( $username )

Returns an instance of Shell::Guess for the given user. If you don't specify a username, the current user gets used. And if no shell can be guessed, a reasonable fallback gets chosen based on your platform. 🫶