不能在 Perl 上用括号分割字符串

Question

For example the following code:

$test_str = 'foo(bar';
@arr = split('(', $test_str);

causes the 500 error

Why?

Answer 1

As ikegami says , split expects a pattern as its first argument. A string will just be converted into a pattern. Because an open parenthesis ( has a special meaning, this will error. You need to escape it.

my @arr = split /\(/, $str;

Answer 2

According to perldoc -f split , the first argument to the split() function is a regular expression /PATTERN/ . So if you were to write this:

split('some text', $string)

it would be equivalent to:

split( m/some text/, $string )

And if some text contains characters that are special in regular expressions, then they will treated as such. So your line:

@arr = split('(', $test_str);

will be treated as:

@arr = split( m/(/, $test_str );

This is likely not what you want, as m/(/ is an invalid (you could say incomplete) regular expression. To match on a literal ( , you need to escape it with a back-slash, so use this instead:

@arr = split( m/\(/, $test_str );

By now you've noticed that Perl tries to be helpful by converting your first argument from the string '(' to the regular expression pattern m/(/ . Although you can pass in a string as the first argument, I don't recommend it -- use m/PATTERN/ instead.

The reason for my recommendation is because:

1. A pattern makes it clear that the first argument is a regular expression pattern, and not just any old string.
2. According to perldoc -f split , there is a special case where you can pass in a string as the first argument:

As a special case, specifying a PATTERN of space (' ') will split on white space just as "split" with no arguments does. Thus, "split(' ')" can be used to emulate awk's default behavior, whereas "split(/ /)" will give you as many null initial fields as there are leading spaces. A "split" on "/\\s+/" is like a "split(' ')" except that any leading whitespace produces a null first field. A "split" with no arguments really does a "split(' ', $_)" internally.

It's good not to confuse the two. So use ' ' as the first argument to split() when you want to use the special case of splitting on whitespace, and use m/PATTERN/ as the first argument for every other case.