Ok now I know that I should be using the sed command and have figured out how to add a new line to a file i.e:
sed '/1/G' myFile
But am still stumped
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Unix example questions
Hi Experts,
Thought i'd have a bash at learning UNIX as I mostly know scripting languages or higher level OO based languages. Got to admin its all a little confusing and I am attempting to example questions I found from various sites. First one is to write a script that takes two arguments a file and a string and inputs the string at top of file and in middle line of file.
I know how to get the number of lines from a file i.e.
wc -w File
But I am unsure how to use that as a variable in my script. All that I have read about variables is simple assignment i.e.
myVariable=This
I dont know how to assign the return of a function to the variable i.e.
myVariable=wc -w File
doesnt seem to work. And I dont think its possible to redirect to variables is it? i.e.
wc -w File > $LineCount
Once I have the line numbers I can determine where to add the string but I wouldnt know how to do this either. I would guess that to add the string in the middle line of the file I would first assign the head lines of a variable then append the var to add the sting then append it to add the tail values. But again I dont know how to assign the results of the Tail and Head returns to a file i.e.
$First=$LineCount/2
$Text= Tail -$First
Am I completely off the mark here with what I am wanting to do? I think i probably am and the other questions are alot harder still.
Thanks in advance,
Chris.
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Answers
Thanks ahoofmann, just one problem here, it says dont use external files and your redirecting to the head and tail files. Is there not a simpler way to add a string to file using sed?
Seems as if I can add a new line to a file with sed i.e.
sed '/3/G' myFile > myFile
I must be able to add a string. I am not sure about the sed syntax though, theres all this talk of
[address[,address]][!]{
command1
command2
}
Which may as well be greek to me.
Thanks, Chris.
> .. it says dont use external files ..
who says? your teacher?
> Is there not a simpler way to add a string to file using sed?
I already sad: cumbersome.
If you stick on sed, then
man sed
it's possible, but more cumbersome as I suggested
otherwise
man awk
> "wc -w File" doesnt just return an integer.
myVariable="`wc File|awk '{print $2}'`"
My teacher?
Ok just read up about awk, thats quite a usefull language. I am still having trouble with the first part though, here:
sed -e "1,$myVariable p" file > head
I dont nessacarily want an answer, just a link to better explain sed and maybe awk too. I cant find anything thats making any sense.
Thanks, Chris.
> sed -ne "1,$myVariable p" file > head
prints from line 1 to line in $myVariable
Bugfix: just seen that I missed the -n option for the sed commands, please use instead
sed -ne "1,$myVariable p" file > head
sed -ne "$myVariable,"'$ p' file > tail
http://www.cs.bell-labs.co
> I cant find anything thats making any sense.
use perl, it can do it all in one
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by: ahoffmannPosted on 2006-06-12 at 13:43:53ID: 16889172
> I dont know how to assign the return of a function to the variable i.e.
myVariable="`wc -w File`"
> Once I have the line numbers I can determine where to add the string but I wouldnt know how to do this either.
sed -e "1,$myVariable p" file > head
sed -e "$myVariable,"'$ p' file > tail
( cat head; echo your line; cat tail) > new file
a bit cumbersome in shell, but something you asked for ;-)