Prevent "echo" from interpreting backslash escapes

Question

I'd like to echo something to a file that contains new line escape sequences, however I would like them to remain escaped. I'm looking for basically the opposite to this question.

echo "part1\npart2" >> file

I would like to look like this in the file

$ cat file
old
part1\npart2

but it looks like

$ cat file
old
part1
part2

That should be the default behaviour https://unix.stackexchange.com/questions/219268/how-to-add-new-lines-when-using-echo -- What operating system and what version of `echo` do you have? — chrki, Apr 20 '17 at 19:30
This would happen if you have the `xpg_echo` shell option set ("expand backslash-escape sequences by default"). Is it? You can check with `shopt xpg_echo`. — Benjamin W., Apr 20 '17 at 19:31
For a portable way, you could use `printf '%s\n' 'part1\npart2' >> file`. — Benjamin W., Apr 20 '17 at 19:33
@BenjaminW. there probably is something wrong with the xpg_echo option. shopt doesn't seem to be installed either. I'm using iterm with zsh — Matthias Michael Engh, Apr 20 '17 at 19:42
Ah, I see. `shopt` is a Bash thing. [Zsh `echo`](http://zsh.sourceforge.net/Doc/Release/Shell-Builtin-Commands.html#Shell-Builtin-Commands) seems to interpret backslashes by default — Benjamin W., Apr 20 '17 at 19:51

Benjamin W. · Accepted Answer · 2020-02-27T22:31:43.880

This is a good example of why POSIX recommends using printf instead of echo (see here, under "application usage"): you don't know what you get with echo¹.

You could get:

A shell builtin echo that does not interpret backslash escapes by default
- Example: the Bash builtin echo has an -e option to enable backslash escape interpretation and checks the xpg_echo shell option
A shell builtin echo that interprets backslash escapes by default
- Examples: zsh, dash
A standalone executable /bin/echo: probably depends on which one – GNU Coreutils echo understands the -e option, like the Bash builtin

The POSIX spec says this (emphasis mine):

The following operands shall be supported:
string
A string to be written to standard output. If the first operand is -n, or if any of the operands contain a <backslash> character, the results are implementation-defined.

So, for a portable solution, we can use printf:

printf '%s\n' 'part1\npart2' >> file

where the \n in the format string will always be interpreted, and the \n in the argument will never be interpreted, resulting in

part1\npart2

being appended to file.

¹ For an exhaustive overview of various behaviours for echo and printf, see echo(1) and printf(1) on in-ulm.de.

Prevent "echo" from interpreting backslash escapes

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