Technology Tales

Adding visual appeal to bash command line scripts with colour variables on Linux

23^rd November 2025

While I was updating some scripts to improve their functionality, I made some unexpected discoveries. One involved adding some colour to the output, and a second will come up later. The colours can be defined as values of variables, as you can see below:

# Colours
RED='\033[0;31m'
GREEN='\033[0;32m'
YELLOW='\033[1;33m'
NC='\033[0m' # no colour

In all cases, \033 is the shell escape sequence while [ is the control sequence initiator and m closes the sequence for colour definitions like we have here. A numeric value of 0 resets things to the default, which is how it is used in the no colour (NC) case that we have above to ensure that the colouration does not overflow beyond the intended text. Otherwise, 31 specifies red, 32 specifies green and 33 specifies yellow, giving options to use later on in the code. All of this is in line with the ANSI standard.

This is how these colour variables get used:

echo -e "\n${YELLOW}$(printf '*' {1..40}) All done $(printf '*' {1..40})${NC}\n"

The above is for an example with yellow text produced using ${YELLOW} segment after the newline sequence (\n)  that is activated b y the -e switch passed to the echo command. This is turned off by the ${NC} portion at the end of the text, again before a terminating newline sequence. One extra addition here is the part that outputs forty asterisks: $(printf '*' {1..40}). You could have $(printf '*%.0s' {1..40}) instead, which is clearer to some because of the null output character sequence %.0s. In the earlier example, I opted for the simpler option.

Something to watch with the SYSODSESCAPECHAR automatic SAS macro variable

10^th October 2021

Recently, a client of mine updated one of their systems from SAS 9.4 M5 to SAS 9.4 M7. Despite performing due diligence regarding changes between the maintenance release, a change in behaviour of the SYSODSESCAPECHAR automatic macro variable surprised them. The macro variable captures the assignment of the ODS escape character used to prefix RTF codes for page numbering and other things. That setting is made using an ODS ESCAPECHAR statement like the following:

ods escapechar="~";

In the M5 release, the tilde character in this example was output by the automatic macro variable, but that changed in the M7 release to 7E, the hexadecimal code for the same and this tripped up one of their validated macro programs used in output production. The adopted solution was to use the escape sequence (ESC) that gave the same outcome that was there before the change. That was less verbose than alternative code changing the hexadecimal code into the expected ASCII character that follows.

data _null_;
    call symput("new",byte(input("&sysodsescapechar.",hex.)));
run;

The above supplies a hexadecimal code to the BYTE function for correct rendering, with the SYMPUT routine assigning the resulting value to a macro variable named new. Just using the escape sequence is far more succinct, though there is now an added validation need once user pilot testing has completed. In my line of business, the updating of code is the quickest part of many such changes; documentation and testing always take longer.