Creating string of repeated characters in shell script [duplicate]

You can get as many NULL bytes as you want from /dev/zero. You can then turn these into other characters. The following prints 16 lowercase a's

head -c 16 < /dev/zero | tr '\0' '\141'

len=100 ch='#'
printf '%*s' "$len" | tr ' ' "$ch"

Easiest and shortest way without a loop

VAR=15

Prints as many dots as VAR says (change the first dot to any other character if you like) with eval :

eval printf '.%.0s' {1..$VAR}

Saves the dotted line in a variable to be used later:

line=$(eval printf '.%.0s' {1..$VAR})
echo "Sign here $line"

-Blatantly stolen from dogbane's answer https://stackoverflow.com/a/5349842/3319298

Edit 1 Note about brace expansions like {1..N} - they are performed early and do NOT expand $VAR, thus the use of eval. The use of eval in a script has security implications, be cautious.

Edit 2: Since I have now switched to fish shell, here is a function defined in config.fish that does this with convenience in that shell:

function line -a char -a length
  printf '%*s\n' $length "" | tr ' ' $char
end

Usage: line = 8 produces ========, line \" 8 produces """""""".

On most systems, you could get away with a simple

N=100
myvar=`perl -e "print '.' x $N;"`

I demonstrated a way to accomplish this task with a single command in another question, assuming it's a fixed number of characters to be produced.

I added an addendum to the end about producing a variable number of repeated characters, which is what you asked for, so my previous answer is relevant here:

https://stackoverflow.com/a/17030976/2284005

I provided a full explanation of how it works there. Here I'll just add the code to accomplish what you're asking for:

    n=20 # This the number of characters you want to produce

    variable=$(printf "%0.s." $(seq 1 $n)) # Fill $variable with $n periods

    echo $variable # Output content of $variable to terminal

Outputs:

....................

The solution without loops:

N=100
myvar=`seq 1 $N | sed 's/.*/./' | tr -d '\n'`

You can use C-style for loops in Bash:

num=100
string=$(for ((i=1; i<=$num; i++));do printf "%s" "#";done;printf "\n")

Or without a loop, using printf without using any externals such as sed or tr:

num=100
printf -v string "%*s" $num ' ' '' $'\n'
string=${string// /#}

num=100
myvar=$(jot -b . -s '' $num)
echo $myvar

When I have to create a string that contains $x repetitions of a known character with $x below a constant value, I use this idiom:

base='....................'
# 0 <= $x <= ${#base}
x=5
expr "x$base" : "x\(.\{$x\}\)"    # Will output '\n' too

Output:

.....