onkar has asked for the wisdom of the Perl Monks concerning the following question:

I am Parsing GNU/Linux configuration file to automate the process. 
CONFIG_TULIP_NAP => y
CONFIG_USB_SISUSBVGA_CO => y
CONFIG_PC30 => m
CONFIG_USB_TES => m
CONFIG_I2C_NFORCE => m
CONFIG_MTD_SBC_GX => m
CONFIG_NTFS_DEBUG => Z
CONFIG_DRM_SI => m
CONFIG_SCSI_ISCSI_ATTR => m
CONFIG_ACPI_SLEE => y
CONFIG_DLCI_MA => 8
CONFIG_SCSI_IPR_DUMP => Z
CONFIG_ECONET_NATIV => y
CONFIG_BRIDG => m
CONFIG_IP_ADVANCED_ROUTE => y
CONFIG_AIC79XX_REG_PRETTY_PRIN => y
CONFIG_IF => m


some of the keys are chopped off 

like CONFIG_BRIDG

there are so many entries in the config file 
with this name.
CONFIG_BRIDGE_NF_EBTABLES=m
CONFIG_BRIDGE_EBT_BROUTE=m
CONFIG_BRIDGE_EBT_T_FILTER=m
CONFIG_BRIDGE_EBT_T_NAT=m
CONFIG_BRIDGE_EBT_802_3=m
CONFIG_BRIDGE_EBT_AMONG=m
CONFIG_BRIDGE_EBT_ARP=m
CONFIG_BRIDGE_EBT_IP=m
CONFIG_BRIDGE_EBT_LIMIT=m
CONFIG_BRIDGE_EBT_MARK=m
CONFIG_BRIDGE_EBT_PKTTYPE=m
CONFIG_BRIDGE_EBT_STP=m
CONFIG_BRIDGE_EBT_VLAN=m
CONFIG_BRIDGE_EBT_ARPREPLY=m
CONFIG_BRIDGE_EBT_DNAT=m
CONFIG_BRIDGE_EBT_MARK_T=m
CONFIG_BRIDGE_EBT_REDIRECT=m
CONFIG_BRIDGE_EBT_SNAT=m
CONFIG_BRIDGE_EBT_LOG=m
CONFIG_BRIDGE_EBT_ULOG=m


similarly,

CONFIG_AIC79XX_REG_PRETTY_PRINT=y

is shown only as 

CONFIG_AIC79XX_REG_PRETTY_PRIN => y

I am maintaining hash with configuration name as
key and value to be y,m,Z

I am puzzled as to why the some keys are getting chopped off
while others are not ?


======
code =>

#!/usr/bin/perl


# This part of the script takes the old config
# file and sets only those options into the new
# config files which are set.


open CONF1 ,"<","config-2.6.18-custom" or die $!;
open CONF2 ,"<","config-2.6.16.27-custom" or die $!;

my @lines1= <CONF1>;
my @lines2= <CONF2>;

sub trim{
   my $string = shift;
   $string =~ s/^\s+|\s+$//g;
   return $string;
}

sub get_config_info_in_mem
{
   my %hash_config = ();
   my ($lref)  = @_;
   my (@lines) = @$lref;

   for $line (@lines)
   {
      if (substr($line,0,6) eq "CONFIG" )
      {
         $i=index($line,"=");
         $val=substr($line,$i+1,length($line)-1-$i);
         $conf=substr($line,0,$i-1);
#      print "$conf=$val\n";
         $conf=trim($conf);
         $val=trim($val);
         $hash_config{$conf} = $val;
      }
      else
      {
         if(substr($line,0,8) eq "# CONFIG")
         {
            $i=index($line,"CONFIG_");
            $i_space=index($line," ",$i+1);
            $conf=substr($line,$i,$i_space-$i);
            $val="Z";
#      print "$conf=$val\n";
            $conf=trim($conf);
            $val=trim($val);
            $hash_config{$conf} = $val;
         }
      }
   }
   return %hash_config;
}

sub print_hash_in_mem
{
   my ($hc) = @_;
   my %hash_config =%$hc;
   while( my($conf,$val) = each(%hash_config))
   {
           print "$conf => $val\n";
   }
}


my %hash_config1=get_config_info_in_mem(\@lines1);
#print $hash_config1."\n";
print_hash_in_mem(\%hash_config1);
# my $hash_config2=get_config_info_in_mem(@lines2);
# print_hash_in_mem(%hash_config2);

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Replies are listed 'Best First'.
Re: Hash , Keys strangely chopped !!
by Transient (Hermit) on Jun 19, 2009 at 17:22 UTC
    As ikegami said above, you need to use $i not $i-1 in the substr. Running the data you listed on my machine resulted in all being chopped (probably because of the lack of spaces before the "=")

    I would suggest, however, using split instead of index and substr. It's simpler and cleaner with no messy index residue! 
    my ( $conf, $val ) = split /=/, $line, 2;

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Re: Hash , Keys strangely chopped !!
by ikegami (Patriarch) on Jun 19, 2009 at 17:15 UTC

    some of the keys are chopped off

    $conf=substr($line,0,$i-1);
    should be
    my $conf=substr($line,0,$i);
    or better yet
    my $conf = substr($line, 0, $i);

    If the "=" is at index $i==4 (the 5th character), you want to extract 4 characters (indexes 0 to 3), not three.

    I am puzzled as to why the some keys are getting chopped off while others are not ?

    They're all getting chopped. Some of them probably have spaces before the "=", so you end up chopping one of the spaces instead of a visible character.

    Finally,
    $val=substr($line,$i+1,length($line)-1-$i);
    can be written simpler as
    $val=substr($line,$i+1);
    and more readably as
    $val = substr($line, $i+1);

    Update: Of course, the following is simpler yet: 

    my ($conf, $val) = map { trim($_) } split(/=/, $line, 2);

    [download]

    Update: Doh! Transient posted a split solution at the same time as my update.

    Update: Removed recommendation to use chomp. It doesn't help since the user trim trailing whitespace.

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      Thanks , my ($conf, $val) = map { trim($_) } split(/=/, $line, 2); worked good for me.
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Re: Hash , Keys strangely chopped !!
by Marshall (Canon) on Jun 20, 2009 at 19:51 UTC
    I don't think that the string functions are the way to go here. I would use regex to make 2 hashes and then merge/adjust them in whatever way that you need. This is some example code: 
    #!/usr/bin/perl -w
use strict;
use Data::Dumper;

open (my $config_file_main   ,"<","config18.txt" )or die $!;
open (my $config_file_update ,"<","config27.txt" )or die $!;

my %file1 = read_cfg ($config_file_main);
my %file2 = read_cfg ($config_file_update);

# this combines both hashes into one !!!!
# A simple "merge" operation.
# More complex things can be done

%file1 = (%file1, %file2);

# Usually it is better to print in
# a human readable format with sort
#
foreach my $key (sort keys %file1)
{
   print "$key = $file1{$key}\n";
}

# This returns a list instead of list ref
# Of course using a ref is more efficient, but here I
# do something simple to illustrate points above..
#
sub read_cfg
{
   my $file_handle = shift;
   my %hash;
   
   while (<$file_handle>)
   {
      next if /^\s*$/;          #skip blank lines
      my ($name,$value) = $_ =~ /^\s*(\S+)\s*=>\s*(\S+)/;
      $hash{$name} = $value;
   }
   close ($file_handle);
   return %hash;   
}

    [download]
    config27:
CONFIG_BRIDGE_NF_EBTABLES => m
CONFIG_BRIDGE_EBT_BROUTE => y
CONFIG_BRIDGE_EBT_T_FILTER => z

    [download]
    config18:
CONFIG_BRIDGE_NF_EBTABLES => m
CONFIG_BRIDGE_EBT_BROUTE => m
CONFIG_BRIDGE_EBT_T_FILTER => m
CONFIG_BRIDGE_EBT_T_NAT => m
CONFIG_BRIDGE_EBT_802_3 => m
CONFIG_BRIDGE_EBT_AMONG => m
CONFIG_BRIDGE_EBT_ARP => m
CONFIG_BRIDGE_EBT_IP => m
CONFIG_BRIDGE_EBT_LIMIT => m
CONFIG_BRIDGE_EBT_MARK => m
CONFIG_BRIDGE_EBT_PKTTYPE => m
CONFIG_BRIDGE_EBT_STP => m
CONFIG_BRIDGE_EBT_VLAN => m
CONFIG_BRIDGE_EBT_ARPREPLY => m
CONFIG_BRIDGE_EBT_DNAT => m
CONFIG_BRIDGE_EBT_MARK_T => m
CONFIG_BRIDGE_EBT_REDIRECT => m
CONFIG_BRIDGE_EBT_SNAT => m
CONFIG_BRIDGE_EBT_LOG => m
CONFIG_BRIDGE_EBT_ULOG => m

    [download]
    Prints: 
    CONFIG_BRIDGE_EBT_802_3 = m
CONFIG_BRIDGE_EBT_AMONG = m
CONFIG_BRIDGE_EBT_ARP = m
CONFIG_BRIDGE_EBT_ARPREPLY = m
CONFIG_BRIDGE_EBT_BROUTE = y
CONFIG_BRIDGE_EBT_DNAT = m
CONFIG_BRIDGE_EBT_IP = m
CONFIG_BRIDGE_EBT_LIMIT = m
CONFIG_BRIDGE_EBT_LOG = m
CONFIG_BRIDGE_EBT_MARK = m
CONFIG_BRIDGE_EBT_MARK_T = m
CONFIG_BRIDGE_EBT_PKTTYPE = m
CONFIG_BRIDGE_EBT_REDIRECT = m
CONFIG_BRIDGE_EBT_SNAT = m
CONFIG_BRIDGE_EBT_STP = m
CONFIG_BRIDGE_EBT_T_FILTER = z
CONFIG_BRIDGE_EBT_T_NAT = m
CONFIG_BRIDGE_EBT_ULOG = m
CONFIG_BRIDGE_EBT_VLAN = m
CONFIG_BRIDGE_NF_EBTABLES = m

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