Linux Bash shell: Leaving some ANSI codes (mostly color) and not interpreting some others from string in a function call

Question

This is an example of my case function:

function SendToScreen(){
echo -e "$*"
}

So I call it by:

SendToScreen "Hello"

And, if I want to add color codes:

VioletForeGroundColor="\033[38;5;99m"
NormalColor="\033[0m"
SendToScreen "Hello"$VioletForeGroundColor" violet "$NormalColor" word."

That gives me a correct:

But the problem comes if I want to send some DOS-type path (including \ slash):

VioletForeGroundColor="\033[38;5;99m"
NormalColor="\033[0m"
MyDOSPath="d:\vivisector"
SendToScreen "Hello"$VioletForeGroundColor" violet "$NormalColor" word. The path is $MyDOSPath"

Because \v is some sort of ANSI code, so this time I obtain:

I need my function to output color text (bold, cursive, underline... etc), so I must use echo -e.

How could I solve the problem with such nagging control codes colliding characters like this \v (I suppose there will be another ones)?

I would like to repair the isssue by modifying the function, but I am not sure this is the proper method.

Thanks.

EDIT-1: We will choose \033 also known as \e as the only ANSI code that needs to remain.

Answer 1

New answer:

function SendToScreen() {
    echo -e $(echo "${*//\\/\\\\}" | sed 's/\\\\033\[/\\033\[/g');
}

This one escapes everything, then un-escapes anything that looks like a color sequence (\033[). The possibility of sending filenames as color sequences is greatly reduced. You can reduce it even further by white-listing only those color sequences that you want to allow, and changing the sed command to a sequence of sed commands that un-escapes those exact sequences.

Old answer: Let's say you want to escape \v and \n, you can do this:

function SendToScreen(){
    a="${*//\\v/\\\\v}"
    a="${a//\\n/\\\\n}"
    echo -e "$a"
}

You can extend this with whatever other escapes you don't want to process.

Answer 2

The echo -e simply interprets sequences starting with backslash, so you simply need to ensure that the $MyDOSPath argument has all backslashes doubled up. That could be:

SendToScreen "Hello ${VioletForeGroundColor}violet${NormalColor} word." \
             "The path is ${MyDOSPath//\\/\\\\}"

which uses a 'substitute' parameter expansion. The // means 'change every backslash to double backslash'.

---

As discussed in various comments, maybe the design of SendToScreen is sub-optimal. One possible alternative design uses:

SendToScreen [-e "string-to-expand"][-p "plain-string"] [-- "plain strings"]

Arguments that need to be expanded are, and those that should not be expanded are not. By default, they're not. So, example usage:

$ VioletForeGroundColor="\033[38;5;99m"
$ NormalColor="\033[0m"
$ MyDOSPath="C:\new\table\value\alert\form\033.txt"
$ echo "$MyDOSPath"
C:\new\table\value\alert\form\033.txt
$ bash SendToScreen.sh -e "${VioletForeGroundColor}violet${NormalColor}" -e "The path is ${MyDOSPath//\\/\\\\}" -p "Or $MyDOSPath" "Plain $MyDOSPath"
violet The path is C:\new\table\value\alert\form\033.txt Or C:\new\table\value\alert\form\033.txt Plain C:\new\table\value\alert\form\033.txt
$  bash SendToScreen.sh -e "${VioletForeGroundColor}violet${NormalColor}" -e "The path is ${MyDOSPath//\\/\\\\}" -p "Or $MyDOSPath" -e "Oops! $MyDOSPath" "Plain $MyDOSPath"
violet The path is C:\new\table\value\alert\form\033.txt Or C:\new\table\value\alert\form\033.txt Oops! C: ew able
              aluelert
                      orm.txt Plain C:\new\table\value\alert\form\033.txt
$

A hex dump of the last lot of output was:

0x0000: 1B 5B 33 38 3B 35 3B 39 39 6D 76 69 6F 6C 65 74   .[38;5;99mviolet
0x0010: 1B 5B 30 6D 20 54 68 65 20 70 61 74 68 20 69 73   .[0m The path is
0x0020: 20 43 3A 5C 6E 65 77 5C 74 61 62 6C 65 5C 76 61    C:\new\table\va
0x0030: 6C 75 65 5C 61 6C 65 72 74 5C 66 6F 72 6D 5C 30   lue\alert\form\0
0x0040: 33 33 2E 74 78 74 20 4F 72 20 43 3A 5C 6E 65 77   33.txt Or C:\new
0x0050: 5C 74 61 62 6C 65 5C 76 61 6C 75 65 5C 61 6C 65   \table\value\ale
0x0060: 72 74 5C 66 6F 72 6D 5C 30 33 33 2E 74 78 74 20   rt\form\033.txt 
0x0070: 4F 6F 70 73 21 20 43 3A 20 65 77 20 61 62 6C 65   Oops! C: ew able
0x0080: 0B 61 6C 75 65 07 6C 65 72 74 0C 6F 72 6D 1B 2E   .alue.lert.orm..
0x0090: 74 78 74 20 50 6C 61 69 6E 20 43 3A 5C 6E 65 77   txt Plain C:\new
0x00A0: 5C 74 61 62 6C 65 5C 76 61 6C 75 65 5C 61 6C 65   \table\value\ale
0x00B0: 72 74 5C 66 6F 72 6D 5C 30 33 33 2E 74 78 74 0A   rt\form\033.txt.
0x00C0:

You'll have to take my word for it that violet appeared in violet.

Clearly, the user (caller) of SendToScreen has to know which arguments should be expanded and which should not. However, it makes it very explicit.

Here's the code I used as a script. Repackaging as a function is left as an exercise for the reader. Extending it to add -c colour (or maybe -f foreground and -b background) is an exercise for the reader.

#!/bin/bash

output=()

while getopts "p:e:" opt
do
  case "$opt" in
    (e) output+=( $(echo -e "$OPTARG") );;
    (p) output+=( "$OPTARG" );;
  esac
done

shift $(($OPTIND - 1))

echo "${output[@]}" "$@"

Have fun!