Linux command to repeat a string n times

Question

Is there any built-in Linux command that allows to output a string that is n times an input string??

Answer 1

adrian@Fourier:~$ printf 'HelloWorld\n%.0s' {1..5}
HelloWorld
HelloWorld
HelloWorld
HelloWorld
HelloWorld
adrian@Fourier:~$

Answer 2

Here's an old-fashioned way that's pretty portable:

yes "HelloWorld" | head -n 10

This is a more conventional version of Adrian Petrescu's answer using brace expansion:

for i in {1..5}
do
    echo "HelloWorld"
done

That's equivalent to:

for i in 1 2 3 4 5

This is a little more concise and dynamic version of pike's answer:

printf -v spaces '%*s' 10 ''; printf '%s\n' ${spaces// /ten}

Answer 3

You can use a trick. Echoing an empty variable does not print anything. So you can write:

echo word$wojek{1..100}

If $wojek1 $wojek2 ... $wojek100 are non-existing variables you will get your word repeated 100 times without anything else.

Answer 4

This can be parameterized and doesn't require a temp variable, FWIW:

printf "%${N}s" | sed 's/ /blah/g'

Or, if $N is the size of a bash array:

echo ${ARR[@]/*/blah}

Answer 5

Quite a few good ways already mentioned. Can't forget about good old seq though:

[john@awesome]$for i in `seq 5`; do echo "Hi";done
Hi
Hi
Hi
Hi
Hi

Answer 6

Perhaps another way that is more general and useful for you:

adrian@Fourier:~$ n=5
adrian@Fourier:~$ for (( c=1; c<=n; c++)) ; do echo "HelloWorld" ; done
HelloWorld
HelloWorld
HelloWorld
HelloWorld
HelloWorld
adrian@Fourier:~$ 

The bash shell is more powerful than most people think :)

Answer 7

Repeat n times, just put n-1 commas between {}:

$ echo 'helloworld'{,,}
helloworld helloworld helloworld

Repeats 'helloworld' twice after the first echo.

Answer 8

No magic here:

seq 5 | awk '{print "Hello World"}'

Answer 9

I've experienced broken pipe warnings with the yes solution, so here's another good alternative:

$ seq 4 | sed -E 's/.+/foo/'
foo
foo
foo
foo

Answer 10

POSIX AWK:

#!/usr/bin/awk -f
function str_repeat(s1, n1) {
   s2 = ""
   for (n2 = 1; n2 <= n1; n2++) {
      s2 = s2 s1
   }
   return s2
}
BEGIN {
   s3 = str_repeat("Sun", 5)
   print s3
}

Or PHP:

<?php
$s3 = str_repeat('Sun', 5);
echo $s3, "\n";

Answer 11

based on what @pike was hinting at

for every character in string echo string

echo ${target//?/$replace}

An example of a heading underlined with = characters

export heading='ABCDEF'; 
export replace='='; 
echo -e "${heading}\n${heading//?/$replace}"

will output

ABCDEF
======

This seems to port between linux and OS X and that makes me happy.

nJoy!

Answer 12

If you're on BSD, you can just use seq.

$ seq -f "Hello, world" 5
Hello, world
Hello, world
Hello, world
Hello, world
Hello, world

Answer 13

Assuming you want something like Perl's x operator, where you don't automatically get a newline between repetitions:

x() {
  # usage: x string num
  for i in $(seq 1 $2); do printf "%s" "$1"; done
  # print a newline only if the string does not end in a newline
  [[ "$1" == "${1%$'\n'}" ]] && echo ""
}

x Hi 10  # ==> HiHiHiHiHiHiHiHiHiHi

x $'Hello World!\n' 3

I explicitly used a for loop because you can't write {1..$n} in bash: brace expansion is done before variable substitution.

Answer 14

Not exactly built in to linux, but if you have python installed..

python
>>>var = "string"
>>>var*n

Or in one line, as commenter suggested:

python -c 'print "This is a test.\n" * 10'

Answer 15

line="==========================="
line=${line:0:10}
${line//"="/"ten "}

outputs

ten ten ten ten ten ten ten ten ten ten

Answer 16

Try this one:

echo $(for i in $(seq 1 100); do printf "-"; done)

Will create (a hundred dash):

---

Answer 17

On macOS and BSD you can use jot

# Print 5 lines of `HelloWorld`
jot -b "HelloWorld" 5

# Print `HelloWorld` 5 times without newlines
jot -s "" -b "HelloWorld" 5

# Print `Hello` 5 times using a different separator which is `World` instead of newline
jot -s "World" -b "Hello" 5

On Linux you can install athena-jot to get it

Like yes, this solution allows for any number of repetition $N and is very fast although not extremely fast like yes or customized native solutions with SIMD and splice which can achieve tens of GBs of data per second

With yes you can print without new lines like this

$ N=10000000
$ WORD=HelloWorld
$ yes $WORD | tr -d '\n' | head -c $(($N * ${#WORD}))

---

Benchmark:

Looping directly with the shell is slow for obvious reasons, therefore will be unsuitable for huge $N values. You'll always need some external tools like yes, sed, tr... for fast output. The brace expansion trick {1..$N} also completely fails when $N is large due to argument list too long error and using variable string replacement like in commonpike's answer will make the shell give up soon due to lack of memory or the OOM will kick in

Below is some results when printing the word following by a new line

$ time bash -c "echo $WORD\$_{1..$N} >/dev/null"

real    0m15.863s
user    0m15.189s
sys 0m0.646s

$ time bash -c "for i in {1..$N}; do echo $WORD; done >/dev/null"

real    0m42.728s
user    0m38.029s
sys 0m4.673s

$ time bash -c "for i in \$(seq $N); do echo $WORD; done >/dev/null"

real    0m43.073s
user    0m39.349s
sys 0m4.507s

As you can see they're very slow. External tools will blow them out

$ time bash -c "printf %${N}s | sed 's/ /$WORD\n/g' >/dev/null"

real    0m1.913s
user    0m1.847s
sys 0m0.071s

$ time jot -b $WORD $N >/dev/null

real    0m1.262s
user    0m1.255s
sys 0m0.005s

$ time yes $WORD | head -n $N >/dev/null

real    0m0.912s
user    0m0.903s
sys 0m0.031s

$ time gyes $WORD | head -n $N >/dev/null

real    0m0.930s
user    0m0.947s
sys 0m0.090s

$ time yes $WORD | ghead -n $N >/dev/null

real    0m0.246s
user    0m0.138s
sys 0m0.213s

$ time gyes $WORD | ghead -n $N >/dev/null

real    0m0.258s
user    0m0.175s
sys 0m0.242s

I'm doing these tests on macOS and in the last 4 tests you can see how terrible BSD tools are compared to GNU tools (prefixed with g due to name clashing with the default BSD tools), even though they're still far faster than the shell

The above cases are with a trailing new line, and when printing without new lines GNU tools also leave BSD tools in the dust

$ time yes $WORD | tr -d '\n' | ghead -c 300M >/dev/null

real    0m26.763s
user    0m26.857s
sys 0m0.381s

$ time gyes $WORD | tr -d '\n' | ghead -c 300M >/dev/null

real    0m27.972s
user    0m28.142s
sys 0m0.598s

$ time yes $WORD | gtr -d '\n' | ghead -c 300M >/dev/null

real    0m1.353s
user    0m0.609s
sys 0m0.981s

$ time gyes $WORD | gtr -d '\n' | ghead -c 300M >/dev/null

real    0m0.980s
user    0m0.785s
sys 0m1.095s