Ruby way to update file lines

[Mark Probert]

Hi.

I have a need to update a config file. It uses '#' as a line comment
marker. The config file looks like:

# file comment
#
name1:foo1:barther
name2:foo2:barther
name3:foo3:barther
name4:foo4:barther

The name:foo combination is unique.

What is the most efficient way to read in the file, update the line, and
then write it back to the file. One update would be to place a '#' in col
1

#name3:foo3:barther

Any thoughts appreciated.

-mark.

 

[Kirk Haines]

On Thu, 19 Aug 2004 10:45:54 +0900, Mark Probert wrote

What is the most efficient way to read in the file, update the line,
and then write it back to the file. One update would be to place a
'#' in col 1

#name3:foo3:barther

Any thoughts appreciated.

Unless the file is very large, my initial thought is just to read the file
to an array. Edit, then rewrite the file.


Kirk Haines

 

[Robert Klemme]

Hi.

I have a need to update a config file. It uses '#' as a line comment
marker. The config file looks like:

# file comment
#
name1:foo1:barther
name2:foo2:barther
name3:foo3:barther
name4:foo4:barther

The name:foo combination is unique.

What is the most efficient way to read in the file, update the line, and
then write it back to the file. One update would be to place a '#' in col
1

#name3:foo3:barther

Any thoughts appreciated.

-mark.

Some code thoughts below

Regards

robert


# match keys
COMMENT = lambda {|key, val| "# #{key}:#{val}"}
DELETE = lambda { nil }

tasks = {
"foo:bar" => COMMENT,
"foo1:bar1" => DELETE,
}

conf = File.readlines("conf.txt")

# manipulate
conf.map! do |line|
if /^([^:]+:[^:]+).*)$/ =~ line && (fun = tasks[$1])
fun.call $1, $2
else
line
end
end

# remove deleted lines
conf.compact!

File.open("conf-1.txt", "w") {|io| io.puts conf }

#
# alternative -----------------------------------------
#

# use regexp as line matcher
tasks = {
/^foo1:bar1:/ => lambda {|line| "# #{line}"},
/^\s*#\s*foo.bar:/ => lambda {|line| line.sub(/^\s*#\s*/, '' )},
}


conf = File.readlines("conf-1.txt")

# manipulate
conf.map! do |line|
p,f = tasks.find {|patt, fun| patt =~ line}
f ? f.call( line ) : line
end

# remove deleted lines
conf.compact!

File.open("conf-2.txt", "w") {|io| io.puts conf }

 

[Kristof Bastiaensen]

Hi.

I have a need to update a config file. It uses '#' as a line comment
marker. The config file looks like:

# file comment
#
name1:foo1:barther
name2:foo2:barther
name3:foo3:barther
name4:foo4:barther

The name:foo combination is unique.

What is the most efficient way to read in the file, update the line, and
then write it back to the file. One update would be to place a '#' in col
1

#name3:foo3:barther

Any thoughts appreciated.

-mark.

You could use inplace edit. This can make ruby work like awk.
For example:

ruby -aF: -ni.bak -e 'print "#" if $F[0] == "name3"' configfile

KB

 

[Mark Probert]

Some code thoughts below

Regards

robert


# match keys
COMMENT = lambda {|key, val| "# #{key}:#{val}"}
DELETE = lambda { nil }

tasks = {
"foo:bar" => COMMENT,
"foo1:bar1" => DELETE,
}

conf = File.readlines("conf.txt")

# manipulate
conf.map! do |line|
if /^([^:]+:[^:]+).*)$/ =~ line && (fun = tasks[$1])
fun.call $1, $2
else
line
end
end

# remove deleted lines
conf.compact!

File.open("conf-1.txt", "w") {|io| io.puts conf }

I liked this one Thanks.

One minor correction: COMMENT and DELETE should be lower case. Ruby 1.8
spits and error about constants otherwise.

-mark.

 

[Robert Klemme]

Some code thoughts below

Regards

robert


# match keys
COMMENT = lambda {|key, val| "# #{key}:#{val}"}
DELETE = lambda { nil }

tasks = {
"foo:bar" => COMMENT,
"foo1:bar1" => DELETE,
}

conf = File.readlines("conf.txt")

# manipulate
conf.map! do |line|
if /^([^:]+:[^:]+).*)$/ =~ line && (fun = tasks[$1])
fun.call $1, $2
else
line
end
end

# remove deleted lines
conf.compact!

File.open("conf-1.txt", "w") {|io| io.puts conf }

I liked this one Thanks.

Thanks, too!

One minor correction: COMMENT and DELETE should be lower case. Ruby 1.8
spits and error about constants otherwise.

They are meant to be constants because they *are* constant. I just put both
variants into a single file but you'll likely need only one of them, don't
you?

Regards

robert

 

[Mark Probert]

They are meant to be constants because they *are* constant. I just
put both variants into a single file but you'll likely need only one
of them, don't you?

When I leave them as constants, Ruby complains with the following error:

deln.rb:37: dynamic constant assignment
COMMENT = lambda {|key, val| "# #{key}:#{val}" }
^

In the end, it worked out well. My code snippet looks like:

# create a function map for the items we want to delete
comment = lambda {|key, val| "# #{key}:#{val}" }
delete = lambda {|key, val| nil }
checkmap = {}
@nodelist.each do |n|
key = "#{n.name}:#{n.ip}"
checkmap[key] = (@remove) ? delete : comment
end

Where I now have the option of making the deletion permanent or just
commenting it out. Which is perfect for my application.

Regards,

-mark.

 

[Robert Klemme]

When I leave them as constants, Ruby complains with the following error:

deln.rb:37: dynamic constant assignment
COMMENT = lambda {|key, val| "# #{key}:#{val}" }
^

Then you got the scoping wrong. Constants should be defined on top level or
class / module scope, otherwise they are of not much use: what do you gain
by reevaluationg and assigning an expression on each method invocation?
That's not what constants are intended for. You probably did something like
this:
SyntaxError: compile error
(irb):2: dynamic constant assignment
def foo() FOO = "bar" end
^
from (irb):2

While it should be

FOO = "bar"
def foo() ... end
# use FOO
or

class Any
FOO = "bar"
# use FOO
end

Both of them don't trigger warnings unless you do multiple assignments to
the same constant:
(irb):2: warning: already initialized constant FOO
=> "bar"

In the end, it worked out well. My code snippet looks like:

# create a function map for the items we want to delete
comment = lambda {|key, val| "# #{key}:#{val}" }
delete = lambda {|key, val| nil }
checkmap = {}
@nodelist.each do |n|
key = "#{n.name}:#{n.ip}"
checkmap[key] = (@remove) ? delete : comment
end

Where I now have the option of making the deletion permanent or just
commenting it out. Which is perfect for my application.

Fine.

robert

 

[Mark Probert]

Then you got the scoping wrong.

You are correct. Thank you for the clarification.

-mark.