Bash: repeat character a variable number of times

Question

Per the questions and ruminations in:

https://unix.stackexchange.com/questions/188658/writing-a-character-n-times-using-the-printf-command

and

I would like to learn how one might go about parameterizing the repeat value for a character/string. For example, the followings works spiffingly:

printf "   ,\n%0.s" {1..5}

However, if I wanted to parameterize '5', say:

num=5

I cannot seem to get the expansion correct to make this work. For instance:

printf "   ,\n%0.s" {1..$((num))}

fails.

Any thoughts/ideas would be most welcome - I reckon there's a way to do this without having to resort to perl or awk so just curious if poss.

Thanks!

brace expansions happens before parameter expansion in bash, one have to resort to `eval` or a C style loop. — Andreas Louv, May 01 '18 at 14:18

score 6 · Answer 1 · answered May 01 '18 at 14:19

6

You can use seq

num=20;
printf '\n%.0s' $(seq $num)

answered May 01 '18 at 14:19

xvan

4,281
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If one resorts to an external command then AWK would be more portable, as `seq` is part of GNU coreutils. – Andreas Louv May 01 '18 at 14:21
Thank you very much for this. Per the other comment, I'd like to stick to something as portable as possible, hence my selection of the eval solution but I appreciate this suggestion and its workaround to the dangers of using eval. – Kid Codester May 01 '18 at 14:46

score 3 · Accepted Answer · answered May 01 '18 at 14:24

3

If you can build the command as a string -- with all the parameter expansion you want -- then you can evaluate it. This prints X num times:

num=10
eval $(echo printf '"X%0.s"' {1..$num})

answered May 01 '18 at 14:24

Rob Davis

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Kicking myself for forgetting eval. Thanks! – Kid Codester May 01 '18 at 14:47

score 0 · Answer 3 · answered May 01 '18 at 17:37

A slighly different approach

$ repeat() {
    local str=$1 n=$2 spaces
    printf -v spaces "%*s" $n " "     # create a string of spaces $n chars long
    printf "%s" "${spaces// /$str}"   # substitute each space with the requested string
}
$ repeat '!' 10
!!!!!!!!!!                     # <= no newline
$ repeat $'   ,\n' 5
   ,
   ,
   ,
   ,
   ,

Bash: repeat character a variable number of times

3 Answers3

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