How can I check if a Perl module is installed on m

Question

I tried to check if XML::Simple is installed in my system or not.

perl -e 'while (<@INC>) { while (<$_/*.pm>) { print "$_\n"; } }'

The above one-liner was used for listing all modules installed in my system. However, it is not listing XML modules.

However, the following executes fine.

perl -e "use XML::Simple "

What might be the issue?

Answer 1

I believe your solution will only look in the root of each directory path contained in the @INC array. You need something recursive, like:

 perl -e 'foreach (@INC) {
    print `find $_ -type f -name "*.pm"`;
 }'

Answer 2

What you're doing there is not recursing into directories. It is only listing the modules in the root directory of the @INC directory.

The module XML::Simple will live in one of the @INC paths under XML/Simple.pm.

What he said above to find specific modules.

CPAN explains how to find all modules here, see How to find installed modules.

Answer 3

For example, to check if the DBI module is installed or not, use

perl -e 'use DBI;'

You will see error if not installed. (from http://www.linuxask.com)

Answer 4

If you're running ActivePerl under Windows:

• C:\>ppm query * to get a list of all installed modules

• C:\>ppm query XML-Simple to check if XML::Simple is installed

Answer 5

while (<@INC>)

This joins the paths in @INC together in a string, separated by spaces, then calls glob() on the string, which then iterates through the space-separated components (unless there are file-globbing meta-characters.)

This doesn't work so well if there are paths in @INC containing spaces, \, [], {}, *, ?, or ~, and there seems to be no reason to avoid the safe alternative:

for (@INC)

Answer 6

Bravo for @user80168's solution (I'm still counting \'s !) but to avoid all the escaping involved with aliases and shells:

%~/ cat ~/bin/perlmod
perl -le'eval qq{require $ARGV[0]; } 
    ? print ( "Found $ARGV[0] Version: ", eval "$ARGV[0]->VERSION" ) 
    : print "Not installed" ' $1

works reasonably well.

Here might be the simplest and most "modern" approach, using Module::Runtime:

perl -MModule::Runtime=use_module -E '
     say "$ARGV[0] ", use_module($ARGV[0])->VERSION' DBI

This will give a useful error if the module is not installed.

Using -MModule::Runtime requires it to be installed (it is not a core module).