Csdrhrt

I have two files, file1.txt and file2.txt, file1.txt is:

perimeter a=10

perimeter b=15

perimeter c=20

file2.txt is:

perimeter a=12

perimeter b=14

Let me know the sed or Perl to override the values in file1.txt

Output of file1.txt should be like:

perimeter a=12

perimeter b=14

perimeter c=20

I have used series of command like

sed -i -e '/parameter//d r file1.txt' file2.txt

awk -F, 'NR==FNR{a[$1]=$0;next;}a[$1]{$0=a[$1]}1' file1.txt file2.txt

awk -F, 'NR==FNR{a[$1]=$0;next;}a[$1]{$0=a[$1]}1' file2.txt file1.txt

None of these are helping.

Something like this maybe? Save this as e.g. script.pl and run via perl script.pl file1.txt file2.txt and it produces your desired output. I've made some assumptions about the file format, such as that there are no blank lines or comments you need to preserve.

#!/usr/bin/env perl

use warnings;

use strict;

use Tie::IxHash;



tie my %hash, 'Tie::IxHash';

while (<>) {

    chomp;

    my ($k,$v) = split /=/, $_, 2;

    $hash{$k} = $v;

}

for my $k (keys %hash) {

    print "$k=$hash{$k}n";

}

Update: A version without the dependency on Tie::IxHash:

use warnings;

use strict;



my (%hash, @keys);

while (<>) {

    chomp;

    my ($key,$value) = split /=/, $_, 2;

    push @keys, $key unless exists $hash{$key};

    $hash{$key} = $value;

}

for my $key (@keys) {

    print "$key=$hash{$key}n";

}

That can also be smushed into a oneliner:

perl -F= -anle 'exists$h{$F[0]}||push@k,$F[0];$h{$F[0]}=$F[1];END{print"$_=$h{$_}"for@k}' file1.txt file2.txt

However note that unlike the script, this oneliner won't work correctly if there are lines with more than one =.

You'll have to be a bit careful about how to actually rewrite the file. Don't do this:

some_program < file1 > file1

Because the shell takes care of the redirections before launching the program, the > redirection will truncate the file before the program gets a chance to read it.

Here are some alternatives:

1. 
   

   explicitly write to a temp file, then overwrite the original

   
   
   

   tmpfile=$(mktemp)
   
   some_program < file1 > "$tmpfile" && mv "$tmpfile" file1
   
   

   
   
   

   Use && so you only mv if the program exited successfully.

   
   


2. 
   

   use the sponge command from the moreutils package

   
   
   

   some_program < file1 | sponge file1
   
   

   
   


3. 
   

   If you're using GNU awk, you can use the -i inplace extension, but you need to adjust the program a bit:

   
   
   

   gawk -i inplace -F= '
   
       NR == FNR {a[$1] = $0; print; next} 
   
       $1 in a {$0 = a[$1]} 
   
       1
   
   ' file{2,1}.txt
   
   

   
   

Options 2 and 3 use a temp file as well, but will take care of the details for you.