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Gnu tool; sed awk echo etc to prepend or append string to a file

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# 1  
Old 02-23-2017
Gnu tool; sed awk echo etc to prepend or append string to a file
Looking to add text to a file, example

File example;
Code:
nodegroups:
  check-hosts: L@host.domain.com,host2.domain.com,host3.domain.com

I need to take a file with a one line list of hosts separated by commas

Code:
host.domain.com,host2.domain.com,host3.domain.com

and prepend the string " check-hosts: L@" to the line of hosts above (line 2). I need to have two spaces before "check-hosts: L@"
My approach has been to prepend the string " check-hosts: L@" to the file containing the line of hosts. but I am open to other ways as long as I can use the file that contains a list of hosts as the starting poing.

Line 1 nodegroups: needs to be above line 2 in my example.
# 2  
Old 02-23-2017
Try:
Code:
cat << EOF > new_file
nodegroups:
  check-hosts: L@$(cat input_file)
EOF

or

Code:
{ 
  printf "nodegroups:\n  check-hosts: L@"
  cat input_file
} > new_file

This User Gave Thanks to Scrutinizer For This Post:
bash_in_my_head
# 3  
Old 02-28-2017
I have been attempting to replace "checkhosts" num=$RANDOM
How can i do this? Currently when i place single quotes, double quotes or no quotes I get an error..
Code:
num=$RANDOM
echo $num


Code:
{    printf "nodegroups:\n  $num: L@"   cat input_file } > new_file

Last edited by RudiC; 02-28-2017 at 04:26 PM..
# 4  
Old 02-28-2017
Difficult to believe.
I can't find an error:
Code:
num=$RANDOM
echo $num
9131
{  printf "nodegroups:\n  $num: L@";   cat file; }
nodegroups:
  9131: L@host.domain.com,host2.domain.com,host3.domain.com

What error message do you get?
# 5  
Old 02-28-2017
Quote:
Originally Posted by bash_in_my_head
I have been attempting to replace "checkhosts" num=$RANDOM
How can i do this? Currently when i place single quotes, double quotes or no quotes I get an error..
Code:
num=$RANDOM
echo $num


Code:
{    printf "nodegroups:\n  $num: L@"   cat input_file } > new_file

There needs to be either a newline or a semi-colon before the closing curly
brace..
# 6  
Old 02-28-2017
Hi Scrutinizer...

AND before 'cat', { printf "nodegroups:\n $num: L@" ; cat input_file ; } > new_file ...
('printf' ought to be formatted correctly for purity.)
This User Gave Thanks to wisecracker For This Post:
Scrutinizer
# 7  
Old 02-28-2017
Exactly Wisecracker, also the correct/recommended way to use printf is to not use values in the format string (first field), but use format specifiers instead:

Code:
{ printf "nodegroups:\n %d: L@" "$num"; cat input_file ;} > new_file

Another thing to note is that the first curly brace must be followed by space (space, tab, newline) (something that was done right here, but good to know)..
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