Bash loop string and add string to it

Question

Hello I want my script to output the following:

string1 string2
string1 string2 string2
string1 string2 string2 string2
string1 string2 string2 string2 string2

Etc. for about 20 times or so.

I've tried the following:

#! /bin/bash
string1=hello
string2=world

#for {i=1;i=<10;i=i+1};
#echo $string1 + $string2
#!/bin/bash
for ((number=1;number < 10;number++))
do
echo $string1 $string3
string2 *10
done;
exit 0

Now I can't find anything on the web about just looping and adding strings.. Thanks for any help! Greets

s1="hello";s2="world"; for i in {1..10}; do s1="$s1 $s2"; echo $s1; done — gtato
– gtato, Commented Feb 7, 2018 at 14:10
@gtato Please don't use brace expansions for iteration. Either use the C-style for loop as seen in the question, or use a while loop for POSIX compatibility. — chepner
– chepner, Commented Feb 7, 2018 at 14:18
@chepner: Oops... First time I heard about that POSIX compatibility. — Pierre François
– Pierre François, Commented Feb 7, 2018 at 14:22
That's worse; now you have an external process generating the full list of values up front instead of having the shell doing it internally. (I should say, {...} is OK for generating non-sequential ranges like {foo,bar,baz}.{txt,png,gif}. Just don't use it for "predictable" sequences you can generate from a formula in constant space.) — chepner
– chepner, Commented Feb 7, 2018 at 14:37

Pierre François · Accepted Answer · 2018-02-07 14:49:51Z

2

Your bash syntax is not correct.

#!/bin/bash

string1=hello
string2=world
output=$string1" "$string2

for i in {1..10} ; do
  echo $output
  output=$output" "$string2
done

Edit: or, taking into account the comments below for the sake of beauty of code:

#!/bin/bash

string1="hello"
string2="world"
output="$string1 $string2"

for ((i = 1; i <= 10; i++)) ; do
  echo "$output"
  output+=" $string2"
done

edited Feb 7, 2018 at 14:49

answered Feb 7, 2018 at 14:20

Pierre François

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4 Comments

A.Villegas Over a year ago

Hi, you also can do this: output+=" $string2"

chepner Over a year ago

output="$string1 $string" would be the more idiomatic quoting style.

tripleee Over a year ago

The other quoting errors should also be fixed. shellcheck.net can provide more detailed diagnostics.

Walter A Over a year ago

With string1+=" $string2" before the echo you can skip both lines with output. Disadvantage of this, is that the value of string1 is changed.

match · Accepted Answer · 2018-02-07 14:27:13Z

1

you can do this by writing to a variable, appending to it in an inner loop and then echo it out:

string1="string1"
string2="string2"
for ((i=1;i<=10;i++)); do
  output="$string1"
  for ((j=1;j<=$i;j++)); do
    output+=" $string2"
  done
  output+=
  echo $output
done

edited Feb 7, 2018 at 14:27

answered Feb 7, 2018 at 14:24

match

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1 Comment

chepner Over a year ago

bash also supports a more concise += operator: output+=" $string2". (Prefer lowercase variables to all-uppercase, which are reserved for the shell.)

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