Полезная информация

Programming Perl

Programming PerlSearch this book
Previous: 3.2.109 posChapter 3
Next: 3.2.111 printf

3.2.110 print

print LIST

This function prints a string or a comma-separated list of strings. The function returns 1 if successful, 0 otherwise. FILEHANDLE may be a scalar variable name (unsubscripted), in which case the variable contains either the name of the actual filehandle or a reference to a filehandle object from one of the object-oriented filehandle packages. FILEHANDLE may also be a block that returns either kind of value:

print { $OK ? "STDOUT" : "STDERR" } "stuff\n";
print { $iohandle[$i] } "stuff\n";

Note that if FILEHANDLE is a variable and the next token is a term, it may be misinterpreted as an operator unless you interpose a + or put parentheses around the arguments. For example:

print $a - 2;   # prints $a - 2 to default filehandle (usually STDOUT)
print $a (- 2); # prints -2 to filehandle specified in $a
print $a -2;    # ditto (weird parsing rules :-)

If FILEHANDLE is omitted, the function prints to the currently selected output filehandle, initially STDOUT. To set the default output filehandle to something other than STDOUT use the select(FILEHANDLE) operation.[7] If LIST is also omitted, prints $_. Note that, because print takes a LIST, anything in the LIST is evaluated in list context, and any subroutine that you call will likely have one or more of its own internal expressions evaluated in list context. Thus, when you say:

[7] Thus, STDOUT isn't really the default filehandle for print. It's merely the default default filehandle.

print OUT <STDIN>;

it is not going to print out the next line from standard input, but all the rest of the lines from standard input up to end-of-file, since that's what <STDIN> returns in list context. Also, remembering the if-it-looks-like-a-function-it-is-a-function rule, be careful not to follow the print keyword with a left parenthesis unless you want the corresponding right parenthesis to terminate the arguments to the print - interpose a + or put parens around all the arguments:

print (1+2)*3, "\n";            # WRONG
print +(1+2)*3, "\n";           # ok
print ((1+2)*3, "\n");          # ok

Previous: 3.2.109 posProgramming PerlNext: 3.2.111 printf
3.2.109 posBook Index3.2.111 printf