It's quite easy for Perl to open a pipe and read from it: $file = "nospace.txt"; open(IN, "cat $file |") ... But the code breaks when the file name contains a space: # This does not work! $file = "yes space.txt"; ... On Windows, these don't work either: # This does not work! $file = "yes space.txt"; ... You need to use a technique called Safe Pipe Opens : $file = "yes space.txt"; $prog = "cat"; ...

Variable Meaning $_ The default or implicit variable. @_ Within a subroutine the array @_ contains the parameters passed to that subroutine. $a, $b Special package variables when using sort() $<digit> Contains the subpattern from the corresponding set of capturing parentheses from the last pattern match, not counting patterns matched in nested blocks that have been exited already. $. Current line number for the last filehandle accessed. $/ The input record separator, newline by default. $| If set to nonzero, forces a flush right away and after every write or print on the currently selected output channel. Default is 0 (regardless of whether the channel is really buffered by the system or not; $| tells you only whether you've asked Perl explicitly to flush after...

The following applies to Bourne, Korn and Bash: $var or ${var} Replaced by the value of var . Use braces to avoid ambiguity. ${var-value} Use the value of var if set, use value otherwise. ${var+value} Use the value of value if var is set, use nothing otherwise. ${var=value} Use the value of var if set, other wise, use value and assign value to var . ${var?value} Use the value of var ; otherwise, print value to standard error and exit the current shell. If value is omitted, a standard error message is printed instead.