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I can change my cursor shape like this:

printf "\x1b[\x31 q" # block :)
printf "\x1b[\x35 q" # ibeam :)

But when I assign that to a variable with %s and expand using printf, it doesn't work:

CURSOR="\x1b[\x3%s q"

printf ${CURSOR} 1 # block :(
printf ${CURSOR} 5 # ibeam :(

How do I fix this?

  • 1
    Possible duplicate of Why does my shell script choke on whitespace or other special characters? or any of the questions linked to Security implications of forgetting to quote a variable in bash/POSIX shells. In short, quote your variables!. – Stéphane Chazelas Apr 19 at 19:45
  • @StéphaneChazelas, Where am I missing double quotes here?! It would have been awesome if this is fixed with a double quotes; Or do you mean quote in some general sense? – Nishant Apr 19 at 19:49
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    Please read those Q&As – Stéphane Chazelas Apr 19 at 19:53
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    In the second set of commands, the arguments printf sees are \x1b[\x3%s, q and 1 (or 5). Since printf reuses format strings until the arguments are exhausted, the format string is printed twice, once with q replacing %s and once with 1 (or 5). You should quote your variables there; otherwise it has a completely different meaning. – muru Apr 19 at 20:20
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    Do you know that printf does not support hex backslash escapes? Your code is not portable as it relies on non-POSIX features. – schily Apr 23 at 16:06
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\x31 is the character 1 and \x35 is 5, so in this case you don't have to use escape sequences.

CURSOR="\x1b[%s q"

printf "${CURSOR}" 1
printf "${CURSOR}" 5
  • I thought I knew a little bit of escaping, now I understand that it is an ocean :-). – Nishant Apr 20 at 9:43
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By using \x3%s, only \x3 is interpreted as an escape sequence, the %s is no longer part of it. If you want to make that part an argument, you'll have to use %b and bring out the whole \x31 to have that interpreted as an escape sequence:

$ printf "\x1b[\x31 q" | od -c
0000000 033   [   1       q
0000005
$ printf "\x1b[%b q" "\x31" | od -c
0000000 033   [   1       q
0000005
  • Thanks for showing how to use debugging tools likeod. I was struggling to print these characters on the screen :-) – Nishant Apr 20 at 9:47

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