CODEWITHSUNDEEP
perl
Herdsman
Herdsman

Reputation: 889

How can I force perl to process args ONLY from stdin and not from a file on command line?

If I have this inline command:

perl -pi -e 's/([\da-f]{2})([\da-f]{2})\s?/\\x$1\\x$2\t/g'

Which is simply to substitute four-digit hex, and add it a 'x' in front. -i used with no filenames on the command line, reading from STDIN. So for params: 0000 0776, results are \x00\x00\x07\x76

I know, that if -n or -p (with printing) called, perl takes <> diamond. But I want to pass args only AFTER command, but perl assumes it as files to read. So how do I force -n or -p to regard args after command to be regular args for <> in program, and not args as files to read?

Also, I do not understand the role of i here. If i would not include it, then I would be adding args line after line (as does <>), but with i, it takes all my args at once?

Upvotes: 0

Views: 242

Answers (2)

mob
mob

Reputation: 118695

If there are no arguments (i.e., if @ARGV is empty), then your one-line script (which implicitly uses <>) will read input from STDIN. So the solution is to clear @ARGV at compile time.

perl -pi -e 'BEGIN{@ARGV=()}
             s/([\da-f]{2})([\da-f]{2})\s?/\\x$1\\x$2\t/g'

Another solution: Force ARGV (the implicit file handle that the base <> operator reads from) to point to STDIN. This solution doesn't clobber your @ARGV, if any.

perl -pi -e 'BEGIN{*ARGV=*STDIN}
             s/([\da-f]{2})([\da-f]{2})\s?/\\x$1\\x$2\t/g'

Upvotes: 6

Grinnz
Grinnz

Reputation: 9231

The -p option is equivalent to the following code:

LINE:
  while (<>) {
      ...             # your program goes here
  } continue {
      print or die "-p destination: $!\n";
  }

-n is the same without the continue block. There's no way to change what it reads from (which is unfortunate, since <<>> and <STDIN> are both safer options), but it's pretty easy to replicate it with your modification (the error checking is rarely necessary here):

perl -e 'while (<STDIN>) { s/([\da-f]{2})([\da-f]{2})\s?/\\x$1\\x$2\t/g } continue { print }'

Upvotes: 4

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