Prepending text to the begining of a file

[pararoly]

Hi All

From the command line you can append text to a file. For example:-

uptime >> uptimeStats.txt

This will append the output of uptime to the file uptimeStats.txt

Is there an equally simple way of adding the text to the begining of the file? "prepending", if you will?. The original contents of the file must persist.

Many thanks
Best wishes
Roly

[peculiar penguin]

Not really. You could dump the text you want to prepend into a temporary file (A), append the other file (B) to it, delete or rename B, rename A to B's original name.

[pararoly]

Hi peculiar penguin

Thank you for your reply, and..

Yeah, kind of what I was expecting.

Many thanks
Roly

[tgalati4]

man cat
man tac

cat firstfile.txt secondfile.txt > combinedfile.txt

[pararoly]

Hi tgalati4

Thank you very much. That has got me a lot further.

All I am actually trying to do is enter a new "note" from the command line and have it added to the start of a text file - full of notes. There is no order or sorting, other than chronological, to the text file.

I tried using ...

cat - file2 > combined

i.e. the dash (-) taking input from the command line. But when I press ctrl+c to finish providing my input, the entire command quits and the combined file is not updated correctly. I hope that makes some sort of sense!?

Then I tried...

echo "My new note, directed at the head of an existing text file" | cat - file2 > combined

This DID work. So that's great, thank you. Any more bright ideas to make it even easier?

Many thanks
roly

edit: obviously I still then need to rename "combined" to "file2"

[sisco311]

I tried using ...

cat - file2 > combined

i.e. the dash (-) taking input from the command line. But when I press ctrl+c to finish providing my input, the entire command quits and the combined file is not updated correctly. I hope that makes some sort of sense!?

Yes, ^C causes the active program to receive a SIGINT signal.

You have to press ^D to indicate the EOF.

http://en.wikipedia.org/wiki/Control-C

http://en.wikipedia.org/wiki/Control-D

[pararoly]

Hi sisco311

Awesome - I suspected there must be a different key combination.

thank you (all) for your help

Best wishes
Roly

- thread solved

[sisco311]

You are welcome!

If you want to add multiple lines, instead of piping echo to the cat command you can use something like:

cat - file << EOF > newfile
line1
line2
line3
EOF

[pararoly]

Hi sisco311

Just tried that - wow, the more I learn about linux the more i love it! it works great!

Can I ask another question....

What is the "<<" operator called. If it has a name? I know that:-

> re-directs output, and
>> appends output, so
<< this waits until the EOF (or whatever) marker is reached?

One day, I hope to become really good at linux - but it is going to take a while to learn it all! haha!

Thank you very much once more.
Best wishes
roly

[kaibob]

All I am actually trying to do is enter a new "note" from the command line and have it added to the start of a text file - full of notes.

If this is something that will be done on a regular basis, you may want to add a function to your bashrc file. I have included a simple example below that is based on your command line. With this you would simply type the name of the function (adt in my example) followed by a space followed by the text to be added to the start of the text file. The text does not have to be quoted. This assumes, of course, that the name of the combined file does not change. You could dress this up in various ways--for example to insert newlines.

adt () {
echo "$*" | cat - combined.txt >> .temp.txt
mv .temp.txt combined.txt
}