Re: curly braces around a lexical file handle

A few functions take an expression in curlies as their first argument:

map    ( { ... } ... )
grep   ( { ... } ... )
print  ( { ... } ... )
exec   ( { ... } ... )
system ( { ... } ... )
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In print's case,

The expression in the curlies must result in the file handle to which print writes data.
In a few special circumstances (including a plain scalar), the curlies around the expression can be omitted.
The entire expression can be omitted in which case the data will be sent to the previously selected handle (normally STDOUT).

In other words,

print $write_fh "$database_query";
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is a shortcut for

print { $write_fh } "$database_query";
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Re^2: curly braces around a lexical file handle by JavaFan (Canon) on May 31, 2010 at 18:40 UTC
Interestingly, in all cases, either the block is optional, or there's an alternative, non-block syntax: `map EXPR, LIST; grep EXPR, LIST; print LIST; print BAREWORD LIST; print $HANDLE LIST; exec STRING; exec LIST; system STRING; system LIST;` [download] And some you missed, also have a non-block syntax: `sort BLOCK LIST; sort SUBNAME LIST; sort LIST; eval BLOCK; eval STRING;` [download] Not sure whether there's a common issue behind this, or that it's just a coincidence.	[reply] [d/l] [select]
Re^3: curly braces around a lexical file handle by ikegami (Patriarch) on May 31, 2010 at 20:26 UTC
You missed `do` (which has a non-block syntax as well).	[reply] [d/l]
Re^2: curly braces around a lexical file handle by Anonymous Monk on May 31, 2010 at 16:44 UTC
Odd that the few special circumstances seem to be the vast majority of uses ;)	[reply]
Re^3: curly braces around a lexical file handle by ikegami (Patriarch) on May 31, 2010 at 16:52 UTC
I suspect that's exactly why they are special.	[reply]