Re^2: File read and strip

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Re^3: File read and strip by Joost (Canon) on Nov 14, 2006 at 20:03 UTC
shift @ARGV removes the first element from @ARGV and returns it. @ARGV contains all the arguments provided to your program. I was asssuming you wanted to call your program like this: `my_program inputfile outputfile` [download] anyway, `my $whatever = <>;` [download] will read a single line from the file(s) as specified in @ARGV. in other words, $whatever will not be the filename but the next (or first) line of the file you passed as an argument. if you don't pass any arguments `<>` will read from STDIN, which means it will usually wait for you to enter a line. See perlop (quoted below:) Note that lines read usually end in a newline character ("\n") while filenames usually do not. `while (<>) { ... # code for each line } is equivalent to the following Perl-like pseudo code: unshift(@ARGV, ’-’) unless @ARGV; while ($ARGV = shift) { open(ARGV, $ARGV); while (<ARGV>) { ... # code for each line } }` [download] $! will contain the last filesystem error, which will make it a lot easier to see what's going wrong if you pass the wrong filename to open(), or don't have permissions etc. See also perlvar. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l] [select]
Re^3: File read and strip by runrig (Abbot) on Nov 14, 2006 at 20:12 UTC
The files are user-input, so the $file=<> has worked fine for me in the past. I think he was assuming that the file name was coming from the command line. @ARGV is the array of command line arguments, so "shift @ARGV" removes and returns the first argument. If you want the user to enter a file name, then it would be a good idea to prompt for it, e.g.: `print "Enter filename: "; chomp(my $file = <STDIN>);` [download] what does the $! in the die function do? See perlvar. It is the error message for system/library calls. You want to check to see if open fails, and if it does, see why it failed.	[reply] [d/l]