perl -e "print qq/Hello world!\n/;"

##</code><code>##

perl -n -e "print qq/$.:\t$_\n/;" textfile.txt

##</code><code>##

while ( <> ) {
    ..........  # Your code goes here.
    print $_;
}

##</code><code>##

perl -pe "s/\bperl\b/Perl/g;" textfile.txt

##</code><code>##

perl -pe "s/\bperl\b/Perl/g;" textfile.txt >temptext.txt

##</code><code>##

perl -pi.bak -e "s/\bperl\b/Perl/g" infile.txt