Shell::Guess

Make an educated guess about the shell in use

SYNOPSIS

guessing shell which called the 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 an arbitrary user's login shell:

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

DESCRIPTION

Shell::Guess makes a reasonably aggressive attempt to determine the shell being employed by the user, either the shell that executed the perl script directly (the "running" shell), or the users' login shell (the "login" shell). It does this by a variety of means available to it, depending on the platform that it is running on.

getpwent

On UNIXy systems with getpwent, that can be used to determine the login shell.
dscl

Under Mac OS X getpwent will typically not provide any useful information, so the dscl command is used instead.
proc file systems

On UNIXy systems with a proc filesystems (such as Linux), Shell::Guess will attempt to use that to determine the running shell.
ps

On UNIXy systems without a proc filesystem, Shell::Guess will use the ps command to determine the running shell.
Win32::Getppid and Win32::Process::List

On Windows if these modules are installed they will be used to determine the running shell. This method can differentiate between PowerShell, command.com and cmd.exe.
ComSpec

If the above method is inconclusive, the ComSpec environment variable will be consulted to differentiate between command.com or cmd.exe (PowerShell cannot be detected in this manner).
reasonable defaults

If the running or login shell cannot be otherwise determined, a reasonable default for your platform will be used as a fallback. Under OpenVMS this is dcl, Windows 95/98 and MS-DOS this is command.com and Windows NT/2000/XP/Vista/7 this is cmd.exe. UNIXy platforms fallback to bourne shell.

The intended use of this module is to enable a Perl developer to write a script that generates shell configurations for the calling shell so they can be imported back into the calling shell using eval and backticks or source. For example, 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";
}

You can then 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

Shell::Config::Generate provides a portable interface for generating such shell configurations, and is designed to work with this module.

CLASS METHODS

These class methods return an instance of Shell::Guess, which can then be interrogated by the instance methods in the next section below.

running_shell

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

Returns an instance of Shell::Guess based on the shell which directly started the current Perl script. If the running shell cannot be determined, it will return the login shell.

login_shell

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

Returns an instance of Shell::Guess for the given user. If no username is specified then the current user will be used. If no shell can be guessed then a reasonable fallback will be chosen based on your platform.