perl -nle"print $_ .  'world'" file
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if that's what the OP means by "stdin or command line", you could also use -p instead of -n:

perl -ple"$_ .= 'world'" file
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if that's what the OP means by "stdin or command line",

Seems it was.

you could also use -p instead of -n:

You could, but I wouldn't as it is less flexible than -n.

If you want to omit some lines from the output, you can't do that if you are also using -l

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

I'd use Getopt::Long (or Getopt::Std, if that's your preference) to tell the program whether the input is on the commandline or not. One convention for this is to expect the input data on the commandline by default, but if a -i (--input) option is present, to read stdin instead.

I don't see why -i is required. If it's not on the command line, then it must be on STDIN, so there's no reason to use -i.

my $input = @ARGV ? shift(@ARGV) : <STDIN>;
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That's the approach <ARGV> uses.

Scalability / future expansion. The program may need other data on the command line unrelated to the need stated in the OP.

Anyway, I didn't say -i is required. I answered the question "How would you...." And this is how I would. If you would do it otherwise, fine.

I like the flexibility of Getopt::Long and simplicity of Getopt::Std. For even simpler and quick solution, I much prefer the -s switch.

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Open source softwares? Share and enjoy. Make profit from them if you can. Yet, share and enjoy!

Need better specs

Shoot. Right you are. What I meant was "how would you emulate the way that grep receives its file argument. It could be via cat file | grep search_string or it could be via grep search_string file"

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Carter's compass: I know I'm on the right track when by deleting something, I'm adding functionality

This is built-in behavior in Perl. From perlrun:

The null filehandle <> is special: it can be used to emulate the behavior of sed and awk. Input from <> comes either from standard input, or from each file listed on the command line. Here’s how it works: the first time <> is evaluated, the @ARGV array is checked, and if it is empty, $ARGV[0] is set to "-", which when opened gives you standard input. The @ARGV array is then processed as a list of filenames.

In that case I would just shift off any required arguments from @ARGV, then process the file list with <> (or manually with open, etc., if I were paranoid about using <>).

$ perl -e 'while(true){print"line? >";$line=<STDIN>;chomp $line;print 
+$line," world\n"}'
line? >line1
line1 world
line? >sttw  rtztrw
sttw  rtztrw world
line? >last line..............
last line.............. world
line? > world
line? > 

$ perl -e 'print "@ARGV"," world\n" if $ARGV[0] || do {while(true){pri
+nt"line? >";$line=<STDIN>;chomp $line;print $line," world\n"}}' "reve
+rse(dlrow) is"
reverse(dlrow) is world
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• Getopt::Long
• Getopt::Clade
• Getopt::Euclid

Getopt-Clade is vaporware.

Using your favorite text editor.

Come on! This is homework! We don't mind helping people with homework if they say as much and ask for pointers. That's not what you did, so no bone for you.

If you say you want to read from STDIN or command line, I guess you want it to behave like cat. I guess someone else needs to understand it too.

while (<>) {
   chomp;
   print "$_ world\n";
}
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