Multiplying strings in bash script

Question

I know that if I do print ("f" + 2 * "o") in python the output will be foo.

But how do I do the same thing in a bash script?

Solution 1

You can use bash command substitution to be more portable across systems than to use a variant specific command.

$ myString=$(printf "%10s");echo ${myString// /m}           # echoes 'm' 10 times
mmmmmmmmmm

$ myString=$(printf "%10s");echo ${myString// /rep}         # echoes 'rep' 10 times
reprepreprepreprepreprepreprep

Wrapping it up in a more usable shell-function

repeatChar() {
    local input="$1"
    local count="$2"
    printf -v myString "%s" "%${count}s"
    printf '%s\n' "${myString// /$input}"
}

$ repeatChar str 10
strstrstrstrstrstrstrstrstrstr

Solution 2

You could simply use loop

$ for i in {1..4}; do echo -n 'm'; done
mmmm

Solution 3

In bash you can use simple string indexing in a similar manner

#!/bin/bash
oos="oooooooooooooo"
n=2
printf "%c%s\n" 'f' ${oos:0:n}

output

foo

Another approach simply concatenates characters into a string

#!/bin/bash
n=2
chr=o
str=
for ((i = 0; i < n; i++)); do 
    str="$str$chr"
done
printf "f%s\n" "$str"

Output

foo

There are several more that can be used as well.

Solution 4

That will do:

printf 'f'; printf 'o%.0s' {1..2}; echo

Look here for explanations on the "multiplying" part.

View more solutions

Comments

[gniourf_gniourf]

Use printf -v myString '%*s' "$count" instead of myString=$(...). And use local to mark your variables local (or drop the local variables and use the parameters directly).

[Inian]

@gniourf_gniourf: Yup, it is a pretty old answer. Will make the change anyway!

[James T.]

You can simplify to $ ${$(printf %10s)// /rep}

[kvantour]

I like this answer most, but I would rewrite it as: printf -- "f%s\n" $(printf -- "o%.0s" {1..2}) . The downside is that it needs a subshell, but it does the job quite well.

[Inian]

@pjh: Fixed it, turned out to be a wrong edit

[pjh]

repeatChar works now. Its handling of counts with leading zeros may be surprising to some though. (repeatChar str 09 fails with an invalid octal number error.)