{"id":312,"date":"2026-10-13T12:52:02","date_gmt":"2026-10-13T12:52:02","guid":{"rendered":"http:\/\/www.scmgalaxy.com\/tutorials\/2012\/04\/05\/difference-between-use-and-require-in-perl\/"},"modified":"2026-10-13T12:52:02","modified_gmt":"2026-10-13T12:52:02","slug":"difference-between-use-and-require-in-perl","status":"publish","type":"post","link":"https:\/\/www.devopsschool.com\/blog\/difference-between-use-and-require-in-perl\/","title":{"rendered":"Perl use vs require: Compile-Time and Runtime Module Loading Explained"},"content":{"rendered":"\n

Originally published on 2012-04-05; fully revised and updated.<\/em><\/p>\n\n\n\n

If you maintain Perl in automation, CI\/CD glue scripts, or legacy operations tooling, choosing between use<\/code> and require<\/code> affects correctness and startup behavior. This article explains what each keyword does, when code is loaded, and how to avoid subtle module-loading mistakes.<\/p>\n\n\n

\n
\"Difference<\/figure>\n<\/div>\n\n\n

What use<\/code> and require<\/code> do<\/h2>\n\n\n\n

use<\/code> is primarily a compile-time convenience. In practical terms, use Module LIST;<\/code> behaves like a compile-time block that loads the module and then calls import<\/code> for you. require<\/code> loads code at runtime when execution reaches that line, and it does not<\/strong> import symbols automatically.<\/p>\n\n\n

use<\/span> Some<\/span>::Module<\/span> qw<\/span>(func1<\/span> func2<\/span>);\n\nBEGIN {\n    require<\/span> Some::Module;\n    Some::Module->import(qw(func1 func2));\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
If you want compile-time loading without<\/em> importing, use use Module ();<\/code>.<\/p>\n\n\n\n
use<\/code> vs require<\/code> comparison<\/h2>\n\n\n\n
Aspect<\/th>use<\/code><\/th>require<\/code><\/th><\/tr><\/thead>
Execution time<\/td>Compile time (via implicit BEGIN<\/code>)<\/td>Runtime (when statement is reached)<\/td><\/tr>
Expected form<\/td>Module name (bareword), optional import list<\/td>Module\/file form, including expressions<\/td><\/tr>
Imports symbols<\/td>Yes, by default<\/td>No (must call import<\/code> explicitly if needed)<\/td><\/tr>
Conditional loading<\/td>Not the usual pattern<\/td>Common and straightforward<\/td><\/tr>
Repeat load behavior<\/td>Uses %INC<\/code> tracking under the hood<\/td>Checks %INC<\/code> to avoid reloading already loaded files<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
Execution flow: compile time vs runtime<\/h2>\n\n\n\n
\nflowchart TD\n    A[Perl starts compilation] --> B[use Module found]\n    B --> C[Load module now]\n    C --> D[Call import now]\n    D --> E[Program enters runtime]\n    E --> F[require Module reached]\n    F --> G{Already loaded}\n    G -- yes --> H[Skip reload and continue]\n    G -- no --> I[Load module at runtime]\n<\/pre>\n\n\n\n
Practical Perl examples<\/h2>\n\n\n\n
Compile-time dependency with exports<\/h3>\n\n\n
use<\/span> strict<\/span>;\nuse<\/span> warnings<\/span>;\nuse<\/span> List<\/span>::Util<\/span> qw<\/span>(sum<\/span>);\n\nmy $total = sum(1<\/span>, 2<\/span>, 3<\/span>);\nprint<\/span> \"$total\\n\"<\/span>;<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Runtime conditional loading<\/h3>\n\n\n
if<\/span> ($ENV{ENABLE_HIRES}) {\n    require<\/span> Time::HiRes;\n    my $started = Time::HiRes::time();\n    print<\/span> \"Started at $started\\n\"<\/span>;\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Dynamic module name from configuration<\/h3>\n\n\n
my $module = $ENV{PLUGIN_MODULE} || 'My::Default::Plugin'<\/span>;\n(my $file = \"$module.pm\"<\/span>) =~ s{::}{\/}g;\n\nrequire<\/span> $file;\nprint<\/span> \"Loaded $module from $file\\n\"<\/span>;<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
For dynamic loading, remember that converting ::<\/code> to \/<\/code> and appending .pm<\/code> is a common pattern when the module name is stored in a variable.<\/p>\n\n\n\n
Commands to verify behavior in your Perl installation<\/h2>\n\n\n
perldoc -f use\nperldoc -f require<\/span>\nperldoc -f do<\/span>\nperldoc perlmod<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Common pitfalls<\/h2>\n\n\n\n
  • Assuming require<\/code> imports symbols automatically (it does not).<\/li>
  • Using require<\/code> for a variable module name without converting it to a file path form.<\/li>
  • Forgetting that load timing differs: use<\/code> at compile time, require<\/code> at runtime.<\/li>
  • Confusing do<\/code> with module loading semantics; it serves a different purpose and should be used intentionally.<\/li><\/ul>\n\n\n\n
    Best practices<\/h2>\n\n\n\n
    • Use use<\/code> for normal, always-required dependencies.<\/li>
    • Use use Module ();<\/code> when you want compile-time loading without imports.<\/li>
    • Use require<\/code> for optional, delayed, or environment-specific dependencies.<\/li>
    • Document module-loading choices in shared scripts so future maintainers understand the timing and import behavior.<\/li><\/ul>\n","protected":false},"excerpt":{"rendered":"
      In Perl, `use` and `require` both load code, but they do it at different times and with different side effects. This guide shows when each is appropriate, how imports work, and patterns that avoid common production bugs.<\/p>\n","protected":false},"author":1,"featured_media":3846,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_joinchat":[],"footnotes":""},"categories":[14],"tags":[175,2577,2578,2576,2573,1980,2575,2574,670],"class_list":["post-312","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-perl","tag-perl","tag-perl-guide","tag-perl-tutorial","tag-perl-use-and-require-difference","tag-require","tag-use","tag-use-and-require-difference-in-perl","tag-use-vs-require-in-perl","tag-what"],"_links":{"self":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/312","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/comments?post=312"}],"version-history":[{"count":4,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/312\/revisions"}],"predecessor-version":[{"id":79176,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/312\/revisions\/79176"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/media\/3846"}],"wp:attachment":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/media?parent=312"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/categories?post=312"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/tags?post=312"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}