I'm printing a message in a Bash script, and I want to colourise a portion of it; for example,
#!/bin/bash
normal='\e[0m'
yellow='\e[33m'
cat <<- EOF
${yellow}Warning:${normal} This script repo is currently located in:
[ more messages... ]
EOF
But when I run in the terminal (tmux
inside gnome-terminal
) the ANSI escape characters are just printed in \
form; for example,
\e[33mWarning\e[0m This scr....
If I move the portion I want to colourise into a printf
command outside the here-doc, it works. For example, this works:
printf "${yellow}Warning:${normal}"
cat <<- EOF
This script repo is currently located in:
[ more messages... ]
EOF
From man bash
– Here Documents:
No parameter and variable expansion, command substitution, arithmetic expansion, or pathname expansion is performed on word. If any characters in word are quoted, the delimiter is the result of quote removal on word, and the lines in the here-document are not expanded. If word is unquoted, all lines of the here-document are subjected to parameter expansion, command substitution, and arithmetic expansion. In the latter case, the character sequence \<newline> is ignored, and
\
must be used to quote the characters\
,$
, and`
.
I can't work out how this would affect ANSI escape codes. Is it possible to use ANSI escape codes in a Bash here document that is cat
ted out?
Best Answer
In your script, these assignments
put those characters literally into the variables, i.e., \e[0m, rather than the escape sequence. You can construct an escape character using
printf
(or some versions ofecho
), e.g.,but you would do much better to use
tput
, as this will work for any correctly set up terminal:Looking at your example, it seems that the version of
printf
you are using treats\e
as the escape character (which may work on your system, but is not generally portable to other systems). To see this, tryand you would see the literal characters:
rather than the escape sequence. Putting those in the
printf
format tellsprintf
to interpret them (if it can).Further reading: