Versions of Echo Vary in Fatally Incompatible Ways

I've been getting back to the basics lately. The following excerpt is from opengroup.org. echo is out. printf is in. I think I remember learning from my mentor, Stu, about 10 years ago...

But instead of integrating this somber fact, I invented all sorts of silly reasons to not adopt printf over echo. One less character. Easier to type. Sounds cooler. Is actually a word. I like delay pedals. Whatever. I wish I had gotten curious about my beliefs instead of rationalizing towards whatever I wanted to be true.

APPLICATION USAGE

It is not possible to use echo portably across all POSIX systems unless both -n (as the first argument) and escape sequences are omitted.

The printf utility can be used portably to emulate any of the traditional behaviors of the echo utility as follows (assuming that IFS has its standard value or is unset):

  • The historic System V echo and the requirements on XSI implementations in this volume of IEEE Std 1003.1-2001 are equivalent to: printf "%b\n" "$*"
  • The BSD echo is equivalent to: if [ "X$1" = "X-n" ] then shift printf "%s" "$*" else printf "%s\n" "$*" fi

New applications are encouraged to use printf instead of echo.

RATIONALE

The echo utility has not been made obsolescent because of its extremely widespread use in historical applications. Conforming applications that wish to do prompting without <newline>s or that could possibly be expecting to echo a -n, should use the printf utility derived from the Ninth Edition system.

As specified, echo writes its arguments in the simplest of ways. The two different historical versions of echo vary in fatally incompatible ways.

The BSD echo checks the first argument for the string -n which causes it to suppress the <newline> that would otherwise follow the final argument in the output.

The System V echo does not support any options, but allows escape sequences within its operands, as described for XSI implementations in the OPERANDS section.

The echo utility does not support Utility Syntax Guideline 10 because historical applications depend on echo to echo all of its arguments, except for the -n option in the BSD version.