Because the Perl syntax for an array slice is @a[ ... ].

If you enable warnings, you'll see that by using $a[1..3], the 1..3 is treated as a flip-flop operator comparing against $., and under most circumstances will produce false, which in the numeric context gets taken as 0:

c:\test>perl -wE"@a = 0..10; say $a[1..3]; say @a[1..3]"
Use of uninitialized value in range (or flip) at -e line 1.
Argument "" isn't numeric in array element at -e line 1.
0
123
[download]

Why is it that this

 perl -lane '$,="\t"; print @F[0..4] ."\t\t\t" . @F[25..30]' file.txt

Does not do what I intended ( for the ranges to be printed by tabs, followed by three blank columns followed by another range). Thankyou for your help!

Because $, is the character used when you give a list of values to the print statement, but you've used '.'s.

Ie. You're giving the print statement a single (concatenated) value, therefore the item separator is never used.

This might achieve your goal:

 perl -lane '$,="\t"; print @F[0..4],  "\t\t\t",  @F[25..30]' file.txt
[download]

but "three blank columns" is a very nebulous concept.

Update: FTR, I might code that as:

print join "\t", @F[0..4], ('')x3, @F[25..30];
[download]

---

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

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

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

The start of some sanity?

thanks, but i got something more strange

vinian@cc:~$ echo "Just another perl monker" | perl -w -lane 'print $F
+[0..3]'
Argument "" isn't numeric in array element at -e line 1, <> line 1.
Just
vinian@cc:~$ echo "Just another perl monker" | perl -w -lane 'print $F
+[1..3]'
another
vinian@cc:~$ echo "Just another perl monker" | perl -w -lane 'print $F
+[2..3]'
Argument "" isn't numeric in array element at -e line 1, <> line 1.
Just
vinian@cc:~$ echo "Just another perl monker" | perl -w -lane 'print $F
+[3..3]'
Argument "" isn't numeric in array element at -e line 1, <> line 1.
Just
[download]

when $F[1..3] there is no warnings and the output is $F[1]

In scalar context, the .. operator with numeric constants is interpreted as line range. As you are reading lines with -n and you are on the first line, 1..3 evaluates to 1. All other ranges evaluate to undef (stringified to ''), because the first line is out of the range, and that's why you get the warning.

You should've used @ again:

$ echo "Just another perl monker" | perl -w -lane 'print @F[1..3]'
anotherperlmonker
$ echo "Just another perl monker" | perl -wanE'say@F[1..3]'
anotherperlmonker
$ echo "Just another perl monker" | perl -w -lane 'print @F[3..3]'
monker
$ echo "Just another perl monker" | perl -wanE'say@F[3..3]'
monker
$
[download]


Enjoy, Have FUN! H.Merijn