Unix: adding a file without a dummy file?

Question

I do not want:

$ cat file > dummy; $ cat header dummy > file 

I want to look like the command below, but at the beginning, and not to the end:

 $ cat header >> file 

Answer 1

You cannot add to the beginning of a file without overwriting the file. The first way you gave is the right way to do it.

Answer 2

This is easy to do in sed if you can embed the title bar directly in the command:

 $ sed -i "1iheader1,header2,header3" 

Or if you really want to read it from a file, you can do this using bash help:

 $ sed -i "1i$(<header)" file 

BEWARE , which "-i" overwrites the input file with the results. If you want sed to back up, change it to "-i.bak" or similar, and of course always check the sample data in the temp directory first to make sure you understand what will happen before you apply to your real data.

Answer 3

The entire dummy file is quite annoying. Here's a 1-linear solution that I just tried, which seems to work.

  echo "`cat header file`" > file 

Ticks make the part inside the quotes first so that it does not complain about the output file, which is the input file. This seems like a hhh solution, but a little shorter. I believe that if the files are really large, this can cause problems, although I seem to have seen the shell complain about the ticks that make the commands take too long. Somewhere, the part that is executed first must be stored in a buffer so that the source text can be overwritten, but the expert is not enough for me to know what / where this buffer will be or how much it can be.

Answer 4

You cannot add a file to a file without reading the entire contents of the file and writing a new file with the added text + contents of the file. Think of a file on Unix as a stream of bytes — it is easy to add to the end of the stream, but there is no easy operation to “rewind” the stream and write to it. Even the search operation at the beginning of the file will overwrite the beginning with any data that you write.

Answer 5

One possibility is to use a document here:

 cat > "prependedfile" << ENDENDEND prepended line(s) `cat "file"` ENDENDEND 

There may be a memory limit for this trick.

Answer 6

Thanks to the correct search query!

 echo "include .headers.java\n$(cat fileObject.java )" > fileObject.java 

Then with the file:

 echo "$(cat .headers.java)\n\n$(cat fileObject.java )" > fileObject.java 

Answer 7

if you want to postpone the “title” to the “file” beforehand, why not add the “file” to the “Title”

 cat file >> header 

Answer 8

The following is a simple c-shell attempt to solve this problem. This "prepend.sh" script takes two parameters:

• $ 1 - File containing pre-added wording.
• $ 2 - The source / target file to be modified.

 #!/bin/csh if (if ./tmp.txt) then rm ./tmp.txt endif cat $1 > ./tmp.txt cat $2 >> ./tmp.txt mv $2 $2.bak mv ./tmp.txt $2