How can I check if a Perl module is installed on my system from the command line?

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?

Financial

@Sinan: you changed the question a bit too much. I think the original question was how to find out where a module is installed. Now it's whether a module is installed. – Supposition

I really have no idea. But considering the current question, your answer is pretty much the best so far. Maybe Chells can enlighten us. – Supposition

@Sinan: why'd you retag from perl-module to perl-modules when the latter is barely used? – Chaffinch

theunixshell.blogspot.in/2012/12/… – Twophase

Answer 1

You can check for a module's installation path by:

perldoc -l XML::Simple

The problem with your one-liner is that, it is not recursively traversing directories/sub-directories. Hence, you get only pragmatic module names as output.

Morgen

Of course, this will only work if the module you are looking for contains POD. – Supposition

@Manni: Should work with most modules (from CPAN) as all of them are documented. – Morgen

Some of them are so well documented that they have their docs in their own .pod files. It's a nice trick that works most of the time with that one little gotcha. – Supposition

This only works if the module contains Pod. Strange but true. – Barnaul

You should use -lm instead of -l. It the's same, except that it also works if the module has no POD. – Colly

@briandfoy I think -l -m makes that work (and also gives the module path if they have a separate .pod file) – Jataka

Unfortunately, on my server perldoc is not installed: "You need to install the perl-doc package to use this program." – Barrelhouse

Answer 2

Quick and dirty:

$ perl -MXML::Simple -e 1

Properly

Although, if you want the version, most people say "perl -MModule\ 999". – Saddlebacked

To the anonymous editor: The correct way would be perl -MDigest::SHA -e 1 rather than perl -Digest::SHA -e 1. – Orelle

I use this one all the time, though i usually do a -e "print( \"got it\n\" )" – Jorum

This is the one I like :). – Arnuad

this answer is better suited for use in a shell function: if ! perl -M$module -e 1 2>/dev/null; then – Melinite

This really helps in discarding any subsequent warnings/errors thrown if we were to use cpan -l to verify modules – Perchance

Answer 3

$ perl -MXML::Simple -le 'print $INC{"XML/Simple.pm"}'

From the perlvar entry on %INC:

• %INC

The hash %INC contains entries for each filename included via the do, require, or use operators. The key is the filename you specified (with module names converted to pathnames), and the value is the location of the file found. The require operator uses this hash to determine whether a particular file has already been included.

If the file was loaded via a hook (e.g. a subroutine reference, see require for a description of these hooks), this hook is by default inserted into %INC in place of a filename. Note, however, that the hook may have set the %INC entry by itself to provide some more specific info.

Chaffinch

Answer 4

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)

Cislunar

Answer 5

If you want to quickly check if a module is installed (at least on Unix systems, with Bash as shell), add this to your .bashrc file:

alias modver="perl -e\"eval qq{use \\\$ARGV[0];\\\\\\\$v=\\\\\\\$\\\${ARGV[0]}::VERSION;};\ print\\\$@?qq{No module found\\n}:\\\$v?qq{Version \\\$v\\n}:qq{Found.\\n};\"\$1"

Then you can:

=> modver XML::Simple
No module found

=> modver DBI
Version 1.607

Muro

I love this. Thank you. – Damaraland

This also works on Korn. But seriously, you need a hobby. – Stamper

Answer 6

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.

Adrien

Answer 7

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)

Jataka

Answer 8

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

Spirometer

Answer 9

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"`;
 }'

Riot

This doesn't properly quote $_; if it contains spaces, it'll break at the words; if it contains ; it'll break the command (shell injection) - quote using either String::ShellQuote or the not-quite optimal solution of using the quotemeta built-in. – Categorical

Answer 10

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).

Heifetz

Answer 11

You can use cpan -D module. See here

In your case cpan -D XML::Simple.

It will tell you where the module is installed as well as if it is up-to-date.

Consecration