Perl reading file, printing unique value from a column

Question

I am new to perl, and i\'d like to achieve the following with perl.

I have a file which contain the following data:

/dev/hda1 /boot ext3 rw          


        

Answer 1

perl -anE '$s{$F[2]}++ }{say for keys %s' file

or

perl -anE '$s{$_}++ or say for $F[2]' file

Answer 2

If you prefer awk:

$ cat file
/dev/hda1 /boot ext3 rw 0 0
/dev/hda1 /boot ext3 rw 0 0

$ awk '!seen[$3]++{print $3}' file
ext3

OR , using cut:

$ cut -d" " -f3 file  | sort | uniq      # or use just sort -u if your version supports it
ext3

Here is perl solution:

$ perl -lane 'print $F[2] unless $seen{$F[2]}++' file
ext3

Here is the perl command line options explanation (from perl -h):

l: enable line ending processing, specifies line terminator
a: autosplit mode with -n or -p (splits $_ into @F)
n: assume "while (<>) { ... }" loop around program
e: one line of program (several -e's allowed, omit programfile)

For a better explanation around these option, please refer: https://blogs.oracle.com/ksplice/entry/the_top_10_tricks_of

Answer 3

#!/usr/bin/perl

my %hash ;
while (<>) {
if (/\s*[^\s]+\s+[^\s]+\s+([^\s]+)\s+.*/) {
    $hash{$1}=1;
}
}
print join("\n",keys(%hash))."\n";

Usage:

 ./<prog-name>.pl file1 fil2 ....