dash and ANSI escape sequences

I come here in search of someone who understands dash/portable scripting better than I do. Today, my Google-foo is failing me.

I am in the process of cleaning up someone else's semi-portable shell script (originally written on FreeBSD). The original script uses colors, in the form of

echo -e "\e[1;32mpassed\e[0m"

"echo" should be avoided in general and any option passed to "echo" is non-portable. In bash, I can easily port this to printf

printf '%b' "\x1b[32;1mpassed\x1b[0m\n"

However, this approach does not work in dash. I have read both the echo and printf sections of the dash manual, and it seems that both "\e" and "\x" are unsupported. Using "%b" allows additional backslash-escape sequences, but only \c and \0.

I know the purpose of dash is to provide an efficient POSIX compliant shell. Is there really no POSIX compliant way to use color? It seems so... 80s. Dash's manpage does state that it supports "backslash notation as defined in ANSI X3.159-1989 (“ANSI C89”)", but I can't find a copy of ANSI C89 online to confirm whether it includes display attributes. ANSI C89 is old, but still... too old for color?

Am I somehow missing some hidden functionality in printf, or is there really no POSIX compliant method of printing colors, or is Dash simply incomplete with its POSIX support in this regard?

Any insight is most appreciated.

---Alex

dash, POSIX, or C89 have nothing to do with colors, it depends on your terminal whether it interprets certain escape sequences as color attributes.
You can print arbitrary bytes in a portable way (i.e. as specified by POSIX) by using octal notation, e.g. escape is 033 in octal:

printf "\033[1;32mpassed\033[0m\n"

Guido Berhoerster

Guido Berhoerster <[email protected]> wrote:

 |You can print arbitrary bytes in a portable way (i.e. as
 |specified by POSIX) by using octal notation, e.g. escape is 033
 |in octal:
 |
 |printf "\033[1;32mpassed\033[0m\n"

That is of course even better.

--steffen

Ahh. Ok.

Understood; I get how this all fits together now.

Thanks for your example and explanation!

---Alex

Alex Waite <[email protected]> wrote:

 |I come here in search of someone who understands dash/portable scripting 
 |better than I do. Today, my Google-foo is failing me.
 |
 |I am in the process of cleaning up someone else's semi-portable shell 
 |script (originally written on FreeBSD). The original script uses colors, 
 |in the form of
 |
 |echo -e "\e[1;32mpassed\e[0m"
 |
 |"echo" should be avoided in general and any option passed to "echo" is 
 |non-portable. In bash, I can easily port this to printf
 |
 |printf '%b' "\x1b[32;1mpassed\x1b[0m\n"
 |
 |However, this approach does not work in dash. I have read both the echo 
 |and printf sections of the dash manual, and it seems that both "\e" and 
 |"\x" are unsupported. Using "%b" allows additional backslash-escape 
 |sequences, but only \c and \0.
 |
 |I know the purpose of dash is to provide an efficient POSIX compliant 
 |shell. Is there really no POSIX compliant way to use color? It seems 
 |so... 80s. Dash's manpage does state that it supports "backslash 
 |notation as defined in ANSI X3.159-1989 (“ANSI C89”)", but I can't find 
 |a copy of ANSI C89 online to confirm whether it includes display 
 |attributes. ANSI C89 is old, but still... too old for color?

Colours have nothing to do with the C programming language, they are an attribute of ISO 6429/ECMA-48 capable terminals.

 |Am I somehow missing some hidden functionality in printf, or is there 
 |really no POSIX compliant method of printing colors, or is Dash simply 
 |incomplete with its POSIX support in this regard?
 |
 |Any insight is most appreciated.

  $ /usr/bin/dash -c 'printf "passed"'

(i.e., the plain control character U+001B, ESCAPE) works for me, also on mksh(1), ksh(1), bash(1), and old Bourne shells that effectively go through my /usr/bin/printf.

|---Alex

--steffen