How to echo line with multiple quotes/special characters into file? - linux

Question

I am trying to echo the following line into a .profile but it keeps getting confused by either the many quotes or special characters.
bind '"e[A": history-search-backward'
I've tried all sorts of things but can't get it nailed.
This is what I currently have:
sudo su -c 'echo "bind \'\"\\e[A\": history-search-backward\'" >> /etc/profile' -
This is what it returns:
su: user '"\e[A": does not exist
Yet if I just use:
echo bind \'\"\\e[A\": history-search-backward\'" >> /home/user/testfile
It works just fine.
I have all manner of "sudo su -c "echo blah..." in the rest of my script that work just fine.
Any ideas?

Answer 1

Try this
sudo su -c $'echo \"bind \'\"\\e[A\": history-search-backward\'\" >> /etc/profile\' -'
From the bash man page:
A single quote may not occur between single quotes, even when preceded by a backslash.
Text quoted by $'...' may contain backslash-escaped quotes, both single and double.
Another option is to add a simpler expression to ~/.inputrc:
echo '"\e[A": history-search-backward' >> ~/.inputrc
There doesn't seem to be a system-wide equivalent of .inputrc that is read by all users. Also, this makes the key binding available to any program that uses readline. If you really do want to restrict it to bash, add a conditional expression:
cat >> ~/.inputrc <<'EOF'
$if Bash
"\e[A": history-search-backward
$endif
EOF

Answer 2

Every character is interpreted literally between single quotes, except ' itself. So you can put a single quote inside a literal string like this: 'single'\''quoted' is the string single'quoted.
Your command is complicated because there are two shells involved: the shell you're running this command from, and the shell that su runs. Note that it's weird to run sudo su since sudo already runs the specified command as root; sudo sh -c … makes more sense. So you need to quote for both. It's usually clearest to use single quotes for the outer shell, and double quotes or single quotes or backslashes for the inner shell.
There's another problem with your command: you're targeting the wrong file. /etc/profile is only read by login shells, whereas the bind command is specific to bash but should be read by all instances of bash, not just login shells. Instead of writing this line to /etc/profile, you should write it to the system-wide bashrc, if there is one (it's usually /etc/bash.bashrc).
sudo sh -c 'echo "bind '\''\"\\e[A\": history-search-backward'\''" >>/etc/bash.bashrc'
You may put this setting directly into the readline configuration file, /etc/inputrc. You'll save on a level of quoting.
sudo sh -c 'echo '\''"\e[A": history-search-backward'\'' >>/etc/inputrc'
An easier way to pass an arbitrary string to a command would be to pass it as input instead of as an argument and use a here document.
sudo sh -c 'cat >>/etc/inputrc' <<'EOF'
"\e[A": history-search-backward
EOF