Ways to append text to a file

I quite like this one, where I can set up a log file at the top of a script and write to it throughout without needing either a global variable or to remember to change all occurrences of a filename:

exec 3>> /tmp/somefile.log
...

echo "This is a log message" >&3
echo "This goes to stdout"
echo "This is written to stderr" >&2

The exec 3>dest construct opens the file dest for writing (use >> for appending, < for reading - just as usual) and attaches it to file descriptor #3. You then get descriptor #1 for stdout, #2 for stderr, and this new #3 for the file dest.

You can join stderr to stdout for the duration of a script with a construct such as exec 2>&1 - there are lots of powerful possibilities. The documentation (man bash) has this to say about it:

exec [-cl] [-a name] [command [arguments]] If command is specified, it replaces the shell. [...] If command is not specified, any redirections take effect in the current shell [...].

Here are few other ways to append text to a file.

1. Using tee

   tee -a file <<< "text text text ..."
   

2. Using awk

   awk 'BEGIN{ printf "text text text ..." >> "file" }'
   

3. Using sed

   sed -i '$a text text text ...' file
   sed -i -e "\$atext text text ..." file
   

Sources:

• How to Append to End of a File in Linux

• SED: insert text after the last line?

Using a here-document approach:

cat <<EOF >> file
> foo
> bar
> baz
> EOF

Tests:

$ cat file
aaaa
bbbb

$ cat <<EOF >> file
> foo
> bar
> baz
> EOF

$ cat file
aaaa
bbbb
foo
bar
baz