perl: fail to substitute negative value

casualzone · 06-05-2012, 01:04 AM

I am using perl script to do some replacement as below:

@file[$line] =~ s/$sub_var_list=\d+/$sub_var_list=$sub_var_list_val/ ;

where #sub_var_list=noise6 in this case

i fail to substitute if noise6=-1, it is due to the negative sign. It is ok if the noise6=1 which is the positive value

part of the content file as below:
+ noise4=1 noise5=1 noise6=-1

pls help

markush · 06-05-2012, 01:11 AM

If both sides of the regex have the same string $sub_var_list, why would you use a variable?

Code:

$file[$line] =~ s/([A-Za-z0-9])=\d+/$1=$sub_var_list_val/ ;

(not tested).

Also you should probably check if you really mean @file[$line] instead of $file[$line]!

Markus

casualzone · 06-05-2012, 02:05 AM

may i know why changing from @file to $file?
I load the whole file into a memory array @file then read line by line of the file.

pan64 · 06-05-2012, 02:19 AM

@file is an array, an element of an array is $file[$index]. This is the usual way, see for example here: http://www.tizag.com/perlT/perlarrays.php

the other problem is the - sign, it is missing from your regexp:

Code:

$file[$line] =~ s/$sub_var_list=-?\d+/$sub_var_list=$sub_var_list_val/ ;

casualzone · 06-05-2012, 03:06 AM

oh ic
using "-?"

thank you very much

pan64 · 06-05-2012, 03:34 AM

yes, \d means a digit, + means at least one (or more), - means the minus sign, ? means zero or one instance (of the previous something)
see regexp quantifiers.

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markush · 06-05-2012, 07:06 AM

Ahh, I did not really understand what the OP means with "-1"....

I would suggest an additional solution

Code:

$file[$line] =~ s/$sub_var_list=[-+]?\d+/$sub_var_list=$sub_var_list_val/ ;

which also is valid in cases where the number comes with a +sign.

And an additional explanation about the difference between @ and $. Perl is very contextsensitive. In your case the substitution is done for a line which is a scalar (a single string) and therefore it is $file[$line].
If you expect to make the substitution for every line in @file you could instead write

Code:

s/$sub_var_list=[-+]?\d+/$sub_var_list=$sub_var_list_val/ for @file ;

which is a loop in a oneliner.

Markus

casualzone · 06-06-2012, 12:14 AM

ok
thanks for your sharing