Re^3: Editing just one column in a file

[BrowserUk]

in reply to Re^2: Editing just one column in a file
in thread Editing just one column in a file

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

[vinian]

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

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

[choroba]

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.

[Tux]

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
$

[vinian]

3ks, Tux, I know it's wrong to use $[ $index_begin .. $index_end ], but i want to why range operator produce strange result in different content( scalar or list).
and also 3ks choroba, i think I got it after seeing what you posted.

[ZWcarp]

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!

[BrowserUk]

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

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];