Thanks for the help drieux. I could have been more explicit in my question to have stated that I want perl.script to exit quietly if there are no files on the command line or if not invoked as the recipient of piped output.
I tested your code (I named the file test.input.source) and ... Case 1. a file is specified - works as desired. > test.input.source test.input.source file test.input.source had 59 number of lines we saw 59 number of lines Case 2. a file is cat'd to test.input.source - works as desired. > cat test.input.source |test.input.source no command line args - switching to STDIN STDIN had 59 number of lines we saw 59 number of lines > Case 3. (this is the difficult case for me) the script is invoked with no file and no pipe to it. I would like the script to end quietly, such as >test.input.source > Instead, it waits for input. > test.input.source no command line args - switching to STDIN and now it waits forever. So I do not want to explicitly open STDIN if there is not a pipe already waiting to send me data. It just dawned on me that I may not be using the correct terminology since "pipe" and "STDIN" probably imply much more than I mean for them to convey. I hope this is more clear. And again, thanks for your help. - Paul -----Original Message----- From: drieux [mailto:[EMAIL PROTECTED] Sent: Tuesday, January 06, 2004 11:20 AM To: Perl Beginners Mailing List Subject: Re: What is the source of my input, file or STDIN? On Jan 6, 2004, at 9:32 AM, [EMAIL PROTECTED] wrote: [..] > So, 1. from within perl.script, how can one tell if the input stream is > coming from > STDIN or a file that was opened by <>? > > 2. If input stream is not coming from STDIN, but a file, how can one > tell which file is the current file (assuming multiple files were > specified on the command line)? This is gonna sound a bit silly, so laugh along with me while I play this out. If you want to know which is the whom For What, why not simply code it that way? As an illustration: <http://www.wetware.com/drieux/pbl/perlTrick/CommandLine/ file_or_stdin.plx> In this case I will walk the @ARGV if there is anything to walk, test that the file exists, then pass it off to a count_lines() function, which will open it and count the number of lines. If there are no arguments at the command line, then we will call count_lines() without a file name. On the inside of the count_lines() function is the trick $file ||= '-'; # we open STDIN unless file either we were passed a file name to open, or we will set $file to '-' so that it will read from STDIN. cf: perldoc -f open ciao drieux --- -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] <http://learn.perl.org/> <http://learn.perl.org/first-response> -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] <http://learn.perl.org/> <http://learn.perl.org/first-response>