I have the following string in bash
str="kallel"
I want to create from str an str2. The str2 contains str duplicated till the length = 20. So the result should be like this:
str2="kallelkallelkallelka"
How to do in in bash?
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4 Answers
$ str="kallel"
$ str2=$(printf "$str%.0s" {1..20})
$ echo "$str2"
kallelkallelkallelkallelkallelkallelkallelkallelkallelkallelkallelkallelkallelkallelkallelkallelkallelkallelkallelkallel
$ str2=$(printf "$str%.0s" {1..3})
$ echo "$str2"
kallelkallelkallel
$ n=5
$ str2=$(printf "$str%.0s" $(seq "$n"))
$ echo "$str2"
kallelkallelkallelkallelkallel
1 Comment
Mark
Gotta say I love this use of printf. It took some noodling, but now I see that printf will repeat it's format string for every argument passed to it (if there are more arguments than replaceable % parameters). The %.0s eats up an argument but adds it to the output as 0 length. Even though it's a little obscure, I think it's a better solution than yes | head | xargs | sed | cut that I presented.
This should work:
str="kallel"
str2="${str}"
while (( ${#str2} < 20 ))
do
str2="${str2}${str}"
done
str2="${str2:0:20}"
5 Comments
devnull
Line #2 (
str2="${str}") is redundant.
twalberg
@devnull How so? It's assigning the value of one variable (
${str}) as the initial value of a second variable (str2) before the loop... It reduces the loop count by one as well as overwriting any previous value str2 might have had, avoiding an explicit str2=""...devnull
str2 is unassigned, so length is zero. Try echo ${#foo}.twalberg
@devnull It's probably unassigned, but I don't know that for sure if this is part of a bigger script. Better to be safe.
lmat - Reinstate Monica
@twalberg I think change "It's probably unassigned" to "It's probably assigned". The longer I've been a developer, the more I think this way.
I am 100% stealing this answer from Bash : Duplicate a string variable n times but I thought it bore repeating (despite being on a 6 year old question):
$ yes "kallel" | head -20 | xargs | sed 's/ //g' | cut -c1-20
kallelkallelkallelka
Comments
I'd go for a while loop personally then cut it at the end.
While the length of str2 is less than 20, add str to str2.
Then, for good measure, we cut at the end to max 20 characters.
#!/bin/bash
str="kallel"
str2=""
while [ ${#str2} -le 20 ]
do
str2=$str2$str
done
str2=`echo $str2 | cut -c1-20`
5 Comments
MOHAMED
error in this line
while [ ${#stringZ} -le 20] line 35: [: missing ]'`
Alberto Zaccagni
There should be a space after
20 and before ]. Fixed.MOHAMED
blocked. looks like infinite loop.
twalberg
Counting the length of
$stringZ will always return the same number, since the loop only modifies $str2 and not $stringZ...
Ewan
sorry guys - just put it together without checking. should work now