newbie question about sed and awk....

[cmfwork]

How do I write to a file using sed and/ or awk.
My problem. I have a file that needs to be updated after and install. I want to script into the installation script to get the input from the user and plop that into the config file.
I can get the line number that I want to change by doing a sed command (sed -n -e /foo/= conf.file > linenum.file) and then reading the line num into a variable. I just don't know how to write the data that I need to write on that line number.

This is my test script so far:
echo "enter some text to write to file here:"
read enteredtext
sed -n -e /foo/= conf.file > linenum.file
read lineNum <linenum.file
# Now I have no clue as to what to do...
# I know that I have to stick foo at the beginning of the
# line that I am inserting (foo <entered text>)
any help? Idea? Am I doing things completely wrong... I know there has to be a better way to accomplish what I am doing
Thanks
-cmf

 

[ElgisRamon]

The general Unix text commands work its's files sequentially, then normally you have to create another modified file and the mv the files around; try this:
[tt]
awk '/Found text/ ~ $0 { print bEfOrE_tExT $0 } ; /Found text/ !~ { print $0 }' < TheFile > TheFile_modified
rm TheFile
mv TheFile_modified TheFile
[tt]

I hope it works...

 

[cmfwork]

Thanks will give it a try.

 

[cmfwork]

Help!!! I am getting the following error now...
awk: Syntax error Context is:
>>> ~ $0 { print bEfOrE_tExT $0 } ; /Found text/ !~ { <<<

Thanks
-CMF

 

[bigscouse]

sed &quot;${NUM}s/^.*/foo &/&quot; < file > file.new
mv file.new file

sed instructions explained: -

Contain the sed commands in double quotes so the the $NUM variable can be interpreted.

$NUM is the line number variable, put {} around NUM to show that the following s is not part of the variable name.

/^.*/ is intepreted as replace all text from the start of line.

/foo &/ means insert &quot;foo &quot; before text to be replaced, & says put the text to be replaced here.

 

[ElgisRamon]

Oops! Sorry

With [tt]awk[/tt] your are telling: When you found a line ($0) with text [tt]Found text[/tt] then print some text and then the line. When you found a line without [tt]Found text[/tt] then print only the line... change the sentences to
[tt]
/Found text/ !~ $0 { print $0 }
[/tt]

... everything else can must be the same.

I hope it works...

 

[cmfwork]

thanks everyone... this has been truly helpful...