In Perl how can I concisely check if a variable is defined and contains a non zero length string

Question

I currently use the following Perl to check if a variable is defined and contains text  I have to check defined first to avoid an  uninitialized value  warning   if  defined  name  amp  amp  length  name  gt  0          do something with  name     Is there a better  presumably more concise  way to write this

User · Answer

You could say    name ne      instead of   length  name  gt  0

User · Answer

The excellent library Type  Tiny provides an framework with which to build type-checking into your  Perl code   What I show here is only the thinnest tip of the iceberg and is using Type  Tiny in the most simplistic and manual way   Be sure to check out the Type  Tiny  Manual for more information   use Types  Common  String qw lt  NonEmptyStr  gt    if   NonEmptyStr- gt check  name            Do something here     NonEmptyStr- gt   name      Throw an exception if validation fails

User · Answer

First  since length always returns a non-negative number   if   length  name     and   if   length  name  gt  0     are equivalent    If you are OK with replacing an undefined value with an empty string  you can use Perl 5 10 s     operator which assigns the RHS to the LHS unless the LHS is defined      usr bin perl  use feature qw  say    use strict  use warnings   my  name   say  nonempty  if length  name          say    name      Note the absence of warnings about an uninitialized variable as  name is assigned the empty string if it is undefined   However  if you do not want to depend on 5 10 being installed  use the functions provided by Scalar  MoreUtils  For example  the above can be written as      usr bin perl  use strict  use warnings   use Scalar  MoreUtils qw  define     my  name   print  nonempty n  if length  name   define  name   print    name  n     If you don t want to clobber  name  use default

User · Answer

if   name          since undef and    both evaluate to false       this should work only when string is defined and non-empty         unless you re expecting someting like  name  0  which is false       notice though that  name  00  is not false

User · Answer

It isn t always possible to do repetitive things in a simple and elegant way   Just do what you always do when you have common code that gets replicated across many projects   Search CPAN  someone may have already the code for you   For this issue I found Scalar  MoreUtils   If you don t find something you like on CPAN  make a module and put the code in a subroutine   package My  String  Util  use strict  use warnings  our  ISA   qw  Exporter    our  EXPORT       our  EXPORT OK   qw  is nonempty    use Carp  qw croak    sub is nonempty           croak  is nonempty   requires an argument           unless       1       no warnings  uninitialized        return  defined    0  and length    0     0       1    head1 BOILERPLATE POD  blah blah blah   head3 is nonempty  Returns true if the argument is defined and has non-zero length       More boilerplate POD    cut   Then in your code call it   use My  String  Util qw  is nonempty     if   is nonempty  name           do something with  name     Or if you object to prototypes and don t object to the extra parens  skip the prototype in the module  and call it like  is nonempty  name

User · Answer

How about  if  length   name               do something with  name     This isn t quite equivalent to your original version  as it will also return false if  name is the numeric value 0 or the string  0   but will behave the same in all other cases   In perl 5 10  or later   the appropriate approach would be to use the defined-or operator instead   use feature   5 10   if  length   name               do something with  name     This will decide what to get the length of based on whether  name is defined  rather than whether it s true  so 0  0  will handle those cases correctly  but it requires a more recent version of perl than many people have available

User · Answer

In cases where I don t care whether the variable is undef or equal to     I usually summarize it as    name      unless defined  name  if  name ne           do something with  name

User · Answer

You often see the check for definedness so you don t have to deal with the warning for using an undef value  and in Perl 5 10 it tells you the offending variable     Use of uninitialized value  name in       So  to get around this warning  people come up with all sorts of code  and that code starts to look like an important part of the solution rather than the bubble gum and duct tape that it is  Sometimes  it s better to show what you are doing by explicitly turning off the warning that you are trying to avoid       no warnings  uninitialized     if  length  name                            In other cases  use some sort of null value instead of the data  With Perl 5 10 s defined-or operator  you can give length an explicit empty string  defined  and give back zero length  instead of the variable that will trigger the warning    use 5 010    if  length   name                                 In Perl 5 12  it s a bit easier because length on an undefined value also returns undefined  That might seem like a bit of silliness  but that pleases the mathematician I might have wanted to be  That doesn t issue a warning  which is the reason this question exists   use 5 012  use warnings   my  name   if  length  name       no warning

User · Answer

As mobrule indicates  you could use the following instead for a small savings   if  defined  name  amp  amp   name ne             do something with  name     You could ditch the defined check and get something even shorter  e g    if   name ne             do something with  name     But in the case where  name is not defined  although the logic flow will work just as intended  if you are using warnings  and you should be   then you ll get the following admonishment   Use of uninitialized value in string ne  So  if there s a chance that  name might not be defined  you really do need to check for definedness first and foremost in order to avoid that warning   As Sinan   n  r points out  you can use Scalar  MoreUtils to get code that does exactly that  checks for definedness  then checks for zero length  out of the box  via the empty   method   use Scalar  MoreUtils qw empty   if not empty  name           do something with  name

[perl] In Perl, how can I concisely check if a $variable is defined and contains a non zero length string?

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