How to concatenate string variables in Bash

Question

In PHP, strings are concatenated together as follows:

$foo = "Hello";
$foo .= " World";

Here, $foo becomes "Hello World".

How is this accomplished in Bash?

Answer 1

I wanted to build a string from a list. Couldn't find an answer for that so I post it here. Here is what I did:

list=(1 2 3 4 5)
string=''

for elm in "${list[@]}"; do
    string="${string} ${elm}"
done

echo ${string}

and then I get the following output:

1 2 3 4 5

Answer 2

$ a=hip
$ b=hop
$ ab=$a$b
$ echo $ab
hiphop
$ echo $a$b
hiphop

Answer 3

If what you are trying to do is to split a string into several lines, you can use a backslash:

$ a="hello\
> world"
$ echo $a
helloworld

With one space in between:

$ a="hello \
> world"
$ echo $a
hello world

This one also adds only one space in between:

$ a="hello \
>      world"
$ echo $a
hello world

Answer 4

You can do this too:

$ var="myscript"

$ echo $var

myscript


$ var=${var}.sh

$ echo $var

myscript.sh

Answer 5

I prefer to use curly brackets ${} for expanding variable in string:

foo="Hello"
foo="${foo} World"
echo $foo
> Hello World

---

Curly brackets will fit to Continuous string usage:

foo="Hello"
foo="${foo}World"
echo $foo
> HelloWorld

Otherwise using foo = "$fooWorld" will not work.

Answer 6

Note that this won't work

foo=HELLO
bar=WORLD
foobar=PREFIX_$foo_$bar

as it seems to drop $foo and leaves you with:

PREFIX_WORLD

but this will work:

foobar=PREFIX_"$foo"_"$bar"

and leave you with the correct output:

PREFIX_HELLO_WORLD