How to accept ARG from PIPE or STDIN?

monkfan has asked for the wisdom of the Perl Monks concerning the following question:

Dear Monks,
I wanted my code to be able to accept the input flexibly, either from PIPE:

$ perl othercode.pl | perl thiscode.pl
[download]

or from STDIN

$ perl thiscode.pl SOMEFILE.txt
[download]

Currently I have this construct. But is there a better way to do it?

#!/usr/bin/perl -w
use strict;

# thiscode.pl

my $file = $ARGV[0];
my @lines;

if($file)
 {@lines = `cat $file`;}
 else
 {@lines = <STDIN>;}  # Update: Also, can I do better than 'slurping' 
+here?

foreach (@lines) {
  #Do my stuff here
}
[download]

Regards,
Edward

Comment on How to accept ARG from PIPE or STDIN? Select or Download Code

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Re: How to accept ARG from PIPE or STDIN? by moot (Chaplain) on Mar 17, 2005 at 01:05 UTC
How about just `@lines = <>;` [download] Your second example is not reading from STDIN, by the way. You probably meant this: `$ perl thiscode.pl < SOMEFILE.txt` [download] Update: Your first example, using the pipe, is reading from STDIN.. but the magic diamond `<>` works for both named arguments (files listed) and STDIN.	[reply] [d/l] [select]
Re: How to accept ARG from PIPE or STDIN? by perlfan (Parson) on Mar 17, 2005 at 02:17 UTC
`while (<>) { # do something with $_ }` [download] This will, assuming $\ has not been messed with, loop for each line of input via: `# cat myfile.txt \| dosomething.pl` [download] and `# dosomething.pl < myfile.txt` [download] If you wanted to do: `#dosomething.pl myfile.txt` [download] ~~You need to get the filename from the first element in @ARGV, the arguments array.~~ You may also want to check out Multiple STDIN sources.	[reply] [d/l] [select]
Re^2: How to accept ARG from PIPE or STDIN? by ikegami (Patriarch) on Mar 17, 2005 at 03:02 UTC
If you wanted to do: `dosomething.pl myfile.txt` [download] You need to get the filename from the first element in @ARGV, the arguments array. You may also want to check out Multiple STDIN sources. No. `<>` treats as a list of file names, and opens each of them in turn. `<>` only reads from STDIN if @ARGV is empty. In other words, `while (<>) { # do something with $_ }` [download] works for all of the following: `cat myfile.txt \| dosomething.pl dosomething.pl < myfile.txt dosomething.pl myfile.txt` [download]	[reply] [d/l] [select]
Re^3: How to accept ARG from PIPE or STDIN? by monkfan (Curate) on Mar 17, 2005 at 03:16 UTC
But how about, if I want to use "die" command in this standard context? `open INFILE, "<$file" or die "$0: Can't open file $file: $!"; while (<INFILE>){ # do something with $_ }` [download] Does it still work? Regards, Edward	[reply] [d/l]
Re^4: How to accept ARG from PIPE or STDIN? by ikegami (Patriarch) on Mar 17, 2005 at 04:34 UTC
Re: How to accept ARG from PIPE or STDIN? by Fletch (Bishop) on Mar 17, 2005 at 04:14 UTC
You could always use the special filename "-" to indicate it should read from STDIN. See "The Minus File" in `perldoc perlopentut`.	[reply] [d/l]