Re: [libvirt] [PATCH] schematestutils.sh: improve shell portability: avoid "echo -e"

Daniel Veillard wrote: printf is most definitely more portable than "echo -e". Note that printf has been a shell built-in in just about every shell in common use for at least 10 years. Documentation everywhere has been telling developers to prefer "printf" over "echo-with-any-options" for nearly 20 years. Here's an excerpt from "info coreutils echo": POSIX does not require support for any options, and says that the behavior of `echo' is implementation-defined if any STRING contains a backslash or if the first argument is `-n'. Portable programs can use the `printf' command if they need to omit trailing newlines or output control characters or backslashes. *Note printf invocation::. While my objection was to "echo -e", plain 'echo "$var"' (where $var may be arbitrary) is not terribly reliable. There are plenty of caveats when using plain "echo". I.e., the first argument must not start with a "-". Using printf the way I do above, even if $cmd or $value starts with "-" or contains backslashes, it will be faithfully reproduced. However, if you use your pair of "echo" commands and some $result starts with "-", you'll get misleading output. Here's the section on "echo" in autoconf's "Limitations of Builtins" section: `echo' The simple `echo' is probably the most surprising source of portability troubles. It is not possible to use `echo' portably unless both options and escape sequences are omitted. Don't expect any option. Do not use backslashes in the arguments, as there is no consensus on their handling. For `echo '\n' | wc -l', the `sh' of Solaris outputs 2, but Bash and Zsh (in `sh' emulation mode) output 1. The problem is truly `echo': all the shells understand `'\n'' as the string composed of a backslash and an `n'. Within a command substitution, `echo 'string\c'' will mess up the internal state of ksh88 on AIX 6.1 so that it will print the first character `s' only, followed by a newline, and then entirely drop the output of the next echo in a command substitution. Because of these problems, do not pass a string containing arbitrary characters to `echo'. For example, `echo "$foo"' is safe only if you know that FOO's value cannot contain backslashes and cannot start with `-'. If this may not be true, `printf' is in general safer and easier to use than `echo' and `echo -n'. Thus, scripts where portability is not a major concern should use `printf '%s\n'' whenever `echo' could fail, and similarly use `printf %s' instead of `echo -n'. For portable shell scripts, instead, it is suggested to use a here-document like this: cat <<EOF $foo EOF Alternatively, M4sh provides `AS_ECHO' and `AS_ECHO_N' macros which choose between various portable implementations: `echo' or `print' where they work, `printf' if it is available, or else other creative tricks in order to work around the above problems.