First I create 3 files:
$ touch alpha bravo carlos
Then I want to save the list to a file:
$ ls > info.txt
However, I always got my info.txt inside:
$ cat info.txt alpha bravo carlos info.txt
It looks like the redirection operator creates my info.txt first.
In this case, my question is. How can I save my list of files before creating the info.txt first?
The main question is about the redirection operator. Why does it act first, and how to delay it so I complete my task first? Using the example above to answer it.
When you redirect a command's output to a file, the shell opens a file handle to the destination file, then runs the command in a child process whose standard output is connected to this file handle. There is no way to change this order, but you can redirect to a file in a different directory if you don't want the ls output to include the new file.
ls >/tmp/info.txt
mv /tmp/info.txt ./
In a production script, you should make sure that the file name is unique and unpredictable.
t=$(mktemp -t lstemp.XXXXXXXXXX) || exit
trap 'rm -f "$t"' INT HUP
ls >"$t"
mv "$t" ./info.txt
Alternatively, capture the output into a variable, and then write that variable to a file.
files=$(ls)
echo "$files" >info.txt
As an aside, probably don't use ls in scripts. If you want a list of files in the current directory
printf '%s\n' *
does that.