How to print variables in Perl

Question

I have some code that looks like  my   ids  nIds   while   lt myFile gt        chomp       ids                  nIds        This should concatenate every line in my myFile  and nIds should be my number of lines  How do I print out my  ids and  nIds   I tried simply print  ids  but Perl complains   my   ids   nIds    is a list  right  With two elements

User · Answer

How do I print out my  ids and  nIds   print   ids n   print   nIds n     I tried simply print  ids  but Perl complains   Complains about what  Uninitialised value  Perhaps your loop was never entered due to an error opening the file  Be sure to check if open returned an error  and make sure you are using use strict  use warnings    my   ids   nIds  is a list  right  With two elements   It s a  very special  function call   ids  nIds is a list with two elements

User · Answer

You should always include all relevant code when asking a question  In this case  the print statement that is the center of your question  The print statement is probably the most crucial piece of information  The second most crucial piece of information is the error  which you also did not include  Next time  include both of those   print  ids should be a fairly hard statement to mess up  but it is possible  Possible reasons     ids is undefined  Gives the warning undefined value in print  ids is out of scope  With use strict  gives fatal warning Global variable  ids needs explicit package name  and otherwise the undefined warning from above  You forgot a semi-colon at the end of the line  You tried to do print  ids  nIds  in which case perl thinks that  ids is supposed to be a filehandle  and you get an error such as print to unopened filehandle    Explanations  1  Should not happen  It might happen if you do something like this  assuming you are not using strict    my  var  while   lt  gt          Var          print  var    Gives the warning for undefined value  because  Var and  var are two different variables    2  Might happen  if you do something like this   if   something        my  var    something happened      print  var    my declares the variable inside the current block  Outside the block  it is out of scope   3  Simple enough  common mistake  easily fixed  Easier to spot with use warnings   4  Also a common mistake  There are a number of ways to correctly print two variables in the same print statement   print   var1  var2      concatenation inside a double quoted string print  var1    var2     concatenation print  var1   var2      supplying print with a list of args     Lastly  some perl magic tips for you   use strict  use warnings     open with explicit direction   lt    check the return value   to make sure open succeeded  Using a lexical filehandle  open my  fh    lt     file txt  or die        read the whole file into an array and   chomp all the lines at once chomp my  file    lt  fh gt    close  fh   my  ids    join       file   my  nIds   scalar  file  print  Number of lines   nIds n   print  Text  n ids n     Reading the whole file into an array is suitable for small files only  otherwise it uses a lot of memory  Usually  line-by-line is preferred   Variations    print   file  is equivalent to  ids   join      file   print  ids    file will return the last index in  file  Since arrays usually start at 0    file   1 is equivalent to scalar  file     You can also do   my  ids  do       local          ids    lt  fh gt       By temporarily  turning off      the input record separator  i e  newline  you will make  lt  fh gt  return the entire file  What  lt  fh gt  really does is read until it finds     then return that string  Note that this will preserve the newlines in  ids   Line-by-line solution   open my  fh    lt     file txt  or die       btw     contains the most recent error my  ids  while   lt  fh gt         chomp       ids             concatenate with string   my  nIds            is Current line number for the last filehandle accessed

User · Answer

print  Number of lines   nids n   print  Content   ids n     How did Perl complain   print  ids should work  though you probably want a newline at the end  either explicitly with print as above or implicitly by using say or -l      If you want to interpolate a variable in a string and have something immediately after it that would looks like part of the variable but isn t  enclose the variable name in      print  foo  ids bar

[perl] How to print variables in Perl

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