Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

Prevent "echo" from interpreting backslash escapes

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
like image 253
Matthias Michael Engh Avatar asked Apr 20 '17 19:04

Matthias Michael Engh


1 Answers

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.

like image 63
Benjamin W. Avatar answered Sep 22 '22 05:09

Benjamin W.