Title: echo and backslash-escaped caracters / new lines: how to write portable scripts ?
Date: 2011-04-08 13:59:45

While writing shell scripts you are using a lot of `echo` but did you
think about portability of this simple statement? Can you say what will
be diplayed, without testing, on your shell, the following tests:

    :::bash
    echo \n \c '\n' '\c' "\n" "\c"
    echo -e \n \c '\n' '\c' "\n" "\c"

? I can't, cause I know that the `echo` behavior is very implementation
dependent, typically in `dash`, `echo -e foo` actually print `-e foo` because
the dash's echo don't parses any options... Here is the bug I found on
one of my shell scripts, simplified to this 9 bytes shell script:

    :::bash
    $ cat /tmp/test.sh
    #!/bin/sh
    echo "$*"
    $ /tmp/test.sh '1\n2'
    1
    2

I'm running Debian Squeeze so my `sh` is a `dash`, and the '\\n' is
interpreted by the dash's echo ... but I don't want it! The only
portable workaround I found is:

    :::bash
    $ cat /tmp/test.sh
    #!/bin/sh
    printf "%s\n" "$*"
    $ /tmp/test.sh '1\n2'
    1\n2

Conclusion: Keep a look at your input, if you don't want
backslash-escaped chars to be interpreted and want to be portable, use
printf! You can keep using echo when you have a full control on the
input, so the `sh` Hello World will forever stay:

    :::bash
    echo "Hello world"
