How do I use variables in single quoted strings?

Question

How do I echo a variable inside single quotes?

echo 'test text "here_is_some_test_text_$counter" "output"' >> ${FILE}

See also https://stackoverflow.com/questions/10067266/when-to-wrap-quotes-around-a-shell-variable — tripleee, Jul 15 '18 at 19:06
See [Difference between single and double quotes in Bash](https://stackoverflow.com/q/6697753/6862601) as well. — codeforester, Sep 13 '18 at 21:53
Related: https://stackoverflow.com/questions/8084389/bash-variable-in-single-quote — Jesse Nickles, Feb 15 '23 at 19:27

score 77 · Accepted Answer · edited Jul 03 '18 at 21:02

77

Variables are expanded in double quoted strings, but not in single quoted strings:

 $ name=World

 $ echo "Hello $name"
 Hello World

 $ echo 'Hello $name'
 Hello $name

If you can simply switch quotes, do so.

If you prefer sticking with single quotes to avoid the additional escaping, you can instead mix and match quotes in the same argument:

 $ echo 'single quoted. '"Double quoted. "'Single quoted again.'
 single quoted. Double quoted. Single quoted again.

 $ echo '"$name" has the value '"$name"
 "$name" has the value World

Applied to your case:

 echo 'test text "here_is_some_test_text_'"$counter"'" "output"' >> "$FILE"

edited Jul 03 '18 at 21:02

Aleks-Daniel Jakimenko-A.

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answered Jan 17 '14 at 17:45

Ignacio Vazquez-Abrams

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Alternatively, `echo "test text \"here_is_some_test_text_$counter\" \"output\""`... Escape the double quotes you don't want the shell to interpret. – twalberg Jan 17 '14 at 18:03
5

Don't forget that you have to quote ``"$FILE"``. – Aleks-Daniel Jakimenko-A. Jan 18 '14 at 04:15
@Aleks-DanielJakimenko-A. [Is it necessary?](https://unix.stackexchange.com/questions/68694/when-is-double-quoting-necessary/68748#68748) – Jul 02 '18 at 20:24
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@JoshDetwiler Long story short: **yes**. The answer you linked is fine and goes into all the details, but quoting a variable never hurts and most often quotes are indeed *required* for proper behavior. – Aleks-Daniel Jakimenko-A. Jul 03 '18 at 21:02
*If you can simply switch quotes* not possible if you're using quote-surrunded JSON (JSON requires double quotes for its values) – DarkTrick Nov 22 '22 at 00:32

score 7 · Answer 2 · answered Jan 17 '14 at 18:07

7

use printf:

printf 'test text "here_is_some_test_text_%s" "output"\n' "$counter" >> ${FILE}

answered Jan 17 '14 at 18:07

glenn jackman

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Please quote ``"$FILE"``. – Aleks-Daniel Jakimenko-A. Jan 18 '14 at 04:14

score 4 · Answer 3 · answered Jan 17 '14 at 18:55

4

Use a heredoc:

cat << EOF >> ${FILE}
test text "here_is_some_test_text_$counter" "output"
EOF

answered Jan 17 '14 at 18:55

William Pursell

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score 3 · Answer 4 · answered Oct 14 '16 at 21:54

3

The most readable, functional way uses curly braces inside double quotes.

'test text "here_is_some_test_text_'"${counter}"'" "output"' >> "${FILE}"

answered Oct 14 '16 at 21:54

Paul Back

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Duplicate of Ignacio Vazquez-Abrams's answer from 10 months back – Jonas Berlin Oct 14 '16 at 22:00
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@JonasBerlin: Not exactly a duplicate, but, given that the alleged improvement is _incidental_ to making the original solution work, this should be a _comment_, not an answer. – mklement0 Oct 14 '16 at 22:06
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Unfortunately I do not have the reputation to leave a comment. – Paul Back Oct 17 '16 at 17:55

score 0 · Answer 5 · answered May 20 '17 at 15:17

You can do it this way:

$ counter=1 eval echo `echo 'test text \
   "here_is_some_test_text_$counter" "output"' | \
   sed -s 's/\"/\\\\"/g'` > file

cat file
test text "here_is_some_test_text_1" "output"

Explanation: Eval command will process a string as command, so after the correct amount of escaping it will produce the desired result.

It says execute the following string as command:

'echo test text \"here_is_some_test_text_$counter\" \"output\"'

Command again in one line:

counter=1 eval echo `echo 'test text "here_is_some_test_text_$counter" "output"' | sed -s 's/\"/\\\\"/g'` > file

score 0 · Answer 6 · answered Jul 03 '17 at 09:07

0

Output a variable wrapped with single quotes:

printf "'"'Hello %s'"'" world

answered Jul 03 '17 at 09:07

Elior Malul

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Doesn't work if your variable contains literal single quotes, so this isn't reliable with unknown values. – Charles Duffy Jan 31 '19 at 20:55

score 0 · Answer 7 · answered Nov 22 '22 at 00:35

0

Adding another pair of single quotes arround the variable solved my problem.

For your case:

echo 'test text "here_is_some_test_text_'$counter'" "output"' >> ${FILE}

answered Nov 22 '22 at 00:35

DarkTrick

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R.Sicart · Answer 8 · 2016-10-18T14:40:23.597

-1

with a subshell:

var='hello' echo 'blah_'`echo $var`' blah blah';

edited Oct 18 '16 at 14:40

answered Jan 17 '14 at 18:32

R.Sicart

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Does not work, echoes ```blah_`echo $var` blah blah``` – Jonas Berlin Oct 14 '16 at 21:57
You're right, needs to be surrounded by double quotes instead of simple quotes. I fixed the answer. – R.Sicart Oct 18 '16 at 14:40
Your new answer will compress any whitespace in `$var`.. please see Ignacio Vazquez-Abrams' answer.. – Jonas Berlin Oct 19 '16 at 19:04
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That's a [useless use of `echo`](http://www.iki.fi/era/unix/award.html#echo). You'll be fine with `'blah_'"$var"' blah blah.'` But that's already in Ignacio's answer. – tripleee Jul 02 '18 at 20:17

How do I use variables in single quoted strings?

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