Re: [tlug] Adding text to the beginning of a file

["Arwyn Hainsworth" <arwynh@example.com>]

On 17/03/07, Dave M G <martin@example.com> wrote:
> Arwyn,
>
> Thanks for responding.
> > Sed is your friend:
> > sed '1,/^#--/ d' < file_with_data_to_replace > tmp_file
> > cat file_with_new_data tmp_file > end_result_file
>
> Thank you for the code and the link. I'm afraid that the tutorial left
> my head spinning a bit. I'm just learning bash shell syntax, and sed
> seems to have a whole new layer of options. I hope it's okay if I ask
> some more questions.
>
> What I've learned is that this line in the above code:
> cat file_with_new_data tmp_file > end_result_file
>
> ... wipes out the whole tmp_file with the contents of file_with_new_data.
>
> If I change it to:
> cat file_with_new_data tmp_file >> end_result_file
>
> ... then it adds the contents of file_with_new_data to the *end* of
> tmp_file. This is better, but actually, what I want to do is stick the
> data on at the beginning. Prepend, not append. I looked up command
> options for "cat" but couldn't find how to do it.

The '>' pipe does wipe the contents of the file, but only at the start
of the pipe. In other words
#> cat file1 file2 > result
is functionally the equivalent of
#> cat file1 > result
#> cat file2 >> result
which is actually what you want.


> Other questions:
>
> 1. Can I use cat to prepend the contents of a variable in the shell
> script? I tried this:
> TEXT="This is text"
> cat $TEXT temp.file >> new.file
>
> ... but what it tried to do was look for three files called "This",
> "is", and "text" to append to the new file.
cat is for files, echo is for text and variables. The following
command should do what you want:
#> TEXT="This is text"
#> echo $TEXT | cat - temp.file > new.file

The '-' represents the standard input. In this case data received from
the '|' pipe.

> 2. How do I execute this on multiple files? Like *.php,  and .class?
By using a loop. Providing your files have no spaces in their names
you might find the for loop useful:
#> for file in `ls`; do
#>   echo "this gets added to the start of each file in the directory"
| cat - $file > tmp
#>   mv tmp $file
#> done

Note that the for loop will iterate over a list of words delimited by
spaces, so if you have spaces in your file names the above won't work.
I use an ugly hack to get it to work, but I suspect someone else knows
a much more elegant way of doing it, so I'm not going to post the
hack.

Arwyn