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I am playing around with shell scripts that use ANSI codes and found that for one reason or another different escape codes are supported depending on your terminal/OS.

In some cases I get a dump of unparsed gunk unexpectedly, which I'm assuming means my terminal (on Mac OS) doesn't support that escape code used, despite having read in a number of places that these mean the same thing:

27 = 033 = 0x1b = ^[ = \e

In searching I found this question about detecting slash-escaped support.

The selected answer sniffs the $TERM value to detect

case $TERM in
  (|color(|?))(([Ekx]|dt|(ai|n)x)term|rxvt|screen*)*)
    PS1=$'\e\]0;$GENERATED_WINDOW_TITLE\a'"$PS1"
esac

But I wonder how reliable that is.

Is there a standard way to check for escape code support (primarily for Bash), or is that script pretty much the run of the mill?

  • Alternatively, what escape code can I use to 'guarantee' the most wide-spread support?
  • What about echo expansion -e?
  • What are general best practices in terms of portability/availability/distribution for scripts that use or reference control codes?

This is a nice read too for anyone else looking for info.

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  • 4
    As mentioned in the documentation you reference: "It is generally not good practice to hard-wire terminal controls into programs. Linux supports a terminfo(5) database of terminal capabilities. Rather than emitting console escape sequences by hand, you will almost always want to use a terminfo-aware screen library or utility such as ncurses(3), tput(1), or reset(1)." – Patrick Oct 6 '14 at 23:21
  • @Patrick - I've been trying a bunch of different things, and tput didnt work for me oob. – qodeninja Oct 6 '14 at 23:37
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    There's no universal way of detecting all supported output sequences. If you're running under a true xterm however, you can query for termcap codes, see "Request Termcap/Terminfo String" in invisible-island.net/xterm/ctlseqs/ctlseqs.html – o11c Oct 7 '14 at 0:01
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Have you got specific operations in mind?

Here is an example of using standout mode, which on many terminals will give a strong visible result:

tput smso; echo hello, world; tput rmso

If you were to pipe the sequence to, say, cat, the highlighting would become an empty operation because a pipe isn't a device that understands standout mode:

( tput smso; echo hello, world; tput rmso ) | cat

Interesting characteristic pairs can be found in man 5 terminfo, some of which are as follows:

  • Standout: smso and rmso
  • Underline: smul and rmul
  • Blink (yes!): blink
  • Doublewide: swidm and rwidm
  • Reverse: rev
  • Cancel all: sgr0
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Actually it is possible to inquire DEC terminals (and their clones and emulations, including xterm) about their capabilities; just not about individual escape sequence support (or its completeness). UNIX generally doesn't use this feature, relying on termcap/terminfo databases (which document the quirks as well).

For reference, the sequences are DA ("Device Attributes", ANSI standard) and DECID ("Identify Terminal", DEC private).

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