81

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

  • 1
    By "built-in linux command" I assume you mean shell command, and since you don't mention which shell you're using, I assume it's bash. You can check this by typing "echo $SHELL" at the command line and you should get something similar to "/bin/bash" back. If you don't, you should edit your answer to specify what it does show. Cheers :) – Adrian Petrescu Dec 22 '09 at 3:12
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    I tagged the question with "bash". I thought that would've been enough. – GetFree Dec 22 '09 at 3:27
  • 1
    Related on Stack Overflow: stackoverflow.com/q/3211891/2157640 – Palec Nov 16 '14 at 14:33

16 Answers 16

90
adrian@Fourier:~$ printf 'HelloWorld\n%.0s' {1..5}
HelloWorld
HelloWorld
HelloWorld
HelloWorld
HelloWorld
adrian@Fourier:~$
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  • 6
    Could you explain how this works? I understand the printf command since it's the same as the one in C/C++. But I dont understand how the {1..5} is expanded and how that works in conjunction with the "%.0s" part. – GetFree Dec 22 '09 at 3:24
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    It's a bit of a hack :) Try running "printf 'HelloWorld %d\n' 1 2 3 4 5" and it'll probably click for you. The %.0s flag is meant to do nothing, just be there to pick up arguments. Then, if bash gets more arguments than it has format specifiers, it will simply print out multiple copies, grabbing as many as it needs. So you get the effect. The output of "printf 'HelloWorld %d%d\n' 1 2 3 4 5 6" probably makes it even clearer. Hope this helps! – Adrian Petrescu Dec 22 '09 at 3:44
  • I see. It's the particular behavior of printf what allows the repetition – GetFree Dec 22 '09 at 3:53
  • 1
    (I should note that, from a purely theoretical standpoint, this is probably the fastest solution since it uses a single shell primitive -- not any external processes. In reality though, let's face it, performance of bash scripts doesn't really matter :) – Adrian Petrescu Dec 22 '09 at 3:53
  • 1
    What is specific to printf is that it will repeatedly apply excess arguments to the format string, "looping" for free. By "excess", I mean that there are more arguments than % placeholders. – Paused until further notice. May 8 '12 at 20:38
77

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' ${spaces// /ten}
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  • How do you get rid of the new lines when using the yes command? – GetFree Dec 22 '09 at 4:16
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    One way is to pipe it through sed -n 'H;${x;s/\n//gp}' or sed -n ':t;${s/\n//gp};N;bt' another is to do echo $(yes "HelloWorld" | head -n 10) which adds a space between each copy of the string. Yet another way is to pipe it through tr -d '\n' which also eliminates the final newline. – Paused until further notice. Dec 22 '09 at 9:08
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    It's like Haskell in a bash shell: Hashell? – wchargin Jan 15 '14 at 5:20
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    The yes solution is pretty neat – piggybox Jun 26 '15 at 20:04
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    @arnsholt: OK, I would use a for loop instead of spawning an external executable (yes). Or capture it once and output it twice like: out=$(my-command); printf '%s\n' "$out" "$out" (printf will apply excess arguments sequentially) or other similar techniques. – Paused until further notice. Aug 3 '16 at 19:15
15

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 ${ARR[@]/*/blah}
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  • 3
    This is the shortest POSIX 7 solution I have seen so far since seq, yes and {1..5} are not POSIX 7. – Ciro Santilli 冠状病毒审查六四事件法轮功 Apr 10 '14 at 11:27
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    You shouldn't mix data into printf's format specifier. What if the data contains format strings? This is the correct way to dynamically specify the "precision" (length): printf '%*s' "$N" - make it a habit to enclose the format string in single quotes to prevent variable expansion there. – Paused until further notice. Jan 5 '19 at 14:22
14

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
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  • This one actually respects a zero, treating it as zero! (The {i..j} trick never returns an empty range.) – JellicleCat Oct 15 '16 at 2:48
12

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.

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  • 1
    It's an ugly ugly hack, and yet I can't help but love it and use it. – 16807 Jul 14 '17 at 17:38
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    Love it! Maybe using $_ instead of $wojek makes the intent clearer. – Mihai Todor Sep 4 '19 at 14:13
11

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 :)

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  • This gets my vote, as it's entirely shell-internal; no forking required. – esm Dec 23 '09 at 18:08
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    What forking are you referring to? The original answer requires none. The output of 'type printf' is 'printf is a shell builtin' and therefore runs within the original bash process. – CodeGnome Apr 17 '12 at 20:17
  • This is the only one so far (yes, printf, for i in {1..5}) that if the n is zero, it returns empty string without exist status of 1. Also due to the mathematical notation for comparison, it is easy to have offset by 1 (e.g by changing the <= to <) – Mehrad Mahmoudian Jun 19 '19 at 8:54
7

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

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

Repeats 'helloworld' twice after the first echo.

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  • 5
    Nice, but what if I want to get n from a variable? – GetFree Jun 28 '12 at 7:32
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    it add an extra space after each 'helloworld' – PADYMKO Mar 7 '17 at 11:28
  • this doesn't seem to let you put newlines in the string either (ie getting helloworld on their own lines) – TankorSmash Feb 1 '19 at 16:54
6

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";
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  • Use this without the awk: while (( c++ < 5 )); do printf 'hello'; done – emf Feb 21 '17 at 8:33
  • POSIXly portable. I like this answer – Sergiy Kolodyazhnyy Jan 13 at 8:15
4

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

$ seq 4 | sed "c foo"
foo
foo
foo
foo
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3

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!

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3

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
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  • 2
    In seq (GNU coreutils) 8.25, this gives seq: format 'Hello, world' has no % directive, forcing a formatting directive to be present. GNU coreutils are used e.g. n many Linux distributions and Cygwin. Including the info here for those missing the info that it works only in BSD seq. – Palec Jun 19 '17 at 10:08
3

No magic here:

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

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2
line="==========================="
line=${line:0:10}
${line//"="/"ten "}

outputs

ten ten ten ten ten ten ten ten ten ten
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  • Maybe a more verbose example: declare c='-----'; c=${c//${c:0:1}/$c}; echo $c # Prints "-" 25 times. – Stephen Niedzielski Jan 2 '13 at 23:02
2

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.

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2

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'
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  • 4
    Not really that useful, since it can't be easily integrated into shell scripts, etc. And since there's about a billion ways to do this in the shell itself, I see little reason to bring out the big guns (i.e Python) for it. – Adrian Petrescu Dec 22 '09 at 3:18
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    I agree with your second point but not the fist...it's easy to integrate into a shell script: python -c 'print "This is a test.\n" * 10' – larsks Dec 22 '09 at 14:26
  • I like the readability of this solution, good reason enough for me. ;) – elias Aug 16 '15 at 20:28
1

Try this one:

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

Will create (a hundred dash):


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