How to compare bash variable with double quotes

Question

I have this code

STATUS=`echo "test"`


if [ $STATUS == "test" ]; then
   exit 0
fi

I have tried everything and i am not able to make it true.

I tried

"$STATUS" == "test"
eval $STATUS == "test"
${STATUS[@]} == "test"

The only thing that worked is

$STATUS == \"test\"

Answer 1

The code in the question works, meaning it will execute the exit 0 statement.

Your

STATUS=`echo "test"`

is the same as

STATUS="test"

and (in this case) as

STATUS=test

i.e. the variable STATUS is assigned test as the value (there are no double quotes in the value).

To test this against the value test, do

if [ "$STATUS" = "test" ]

or

if [[ $STATUS == "test" ]]

If STATUS has the value "test", as in

STATUS='"test"'

then use that string in the comparison:

if [ "$STATUS" = '"test"' ]

or

if [[ $STATUS == '"test"' ]]

See also:

• What is the difference between the Bash operators [[ vs [ vs ( vs ((?
• what are the differences between `==` and `=` in conditional expressions?

Answer 2

Those escaped quotes in \"test\" make me think that there's some confusion about the quoting rules of shell, because the first piece of code works as intended and $STATUS == \"test\" shouldn't (unless you wrote STATUS=`echo '"test"'` or something similar).

To properly clarify this confusion, it is needed to explain some shell concepts.

---

Quoting

In POSIX shells, quoting is one of the most important mechanisms. Unfortunately, it is also a very confusing topic and, when used incorrectly, a big source of bugs and weird behavior in scripts.

The basic rules are the following:

1. Escape character \: Preserves the literal value of the next character that follows, with the exception of <newline>.
2. Double quotes ": Preserves the literal value of all characters within the quotes, with the exception of $, `, \ and, when history expansion is enabled, !.
3. Single quotes ': Preserves the literal value of all characters within the quotes, without exceptions.

Command substitution

Command substitution allows the output of a command to replace the command itself. Its syntax is either $(command) or `command`, although the former is prefered.

Test command

The test command (also known as [ in POSIX and [[ in shells like bash, ksh and zsh) let you use many useful conditional and arithmetical expressions. For example, it can check if a given regular file exists and is readable, if two strings are equal or if a number is greater than another.

---

Now, analyzing the code:

STATUS=`echo "test"`

The command substitution here is useless, as it could have been written as STATUS="test". Note that the double quotes are not printed by echo, so STATUS holds test as its value.

if [ $STATUS == "test" ]; then
   exit 0
fi

Here are, at least, 3 potential flaws:

1. The unquoted $STATUS could be affected by word splitting.
2. == is non-POSIX syntax. Use = if you care about portability.
3. if and exit 0 are useless in this scenario as [ already does the intended job.

Also, note that, as the previous line of code, the double quotes are not taken literally, so the resulting command (after expansion and quote removal) is [ test = test ], which is true.

---

But if your goal was to have "test" as the value of STATUS, then

STATUS=\"test\"
STATUS="\"test\""
STATUS='"test"'

are all valid assignments and

[ "$STATUS" = \"test\" ]
[ "$STATUS" = "\"test\"" ]
[ "$STATUS" = '"test"' ]

are all valid conditional expressions.

Answer 3

The solution to this problem may differ based on what shell you are using. Also, ensure that $STATUS contains "test" before the compare with a "echo $STATUS" line in your script. Checking the contents of variables is very helpful for debugging. Although unlikely, there is a small chance some other program is setting it, in which case it will obviously fail.

Generally speaking though, the code you have written SHOULD work. If it isn't the problem might have to be with any other code in the script, the shell itself or some other program interfering. You can try exporting the variable system wide with export to ensure it's set properly. This should override any interfering values. Keep in mind if another program is interfering, it might not like it's variables getting changed.

As a reference, I will provide the following information:

The best way to set a variable to a simple state like "test" is simply:

VARIABLE="value"

While you can use echo to return text into a variable, for strings like test, there's no reason for it. Unless you intend to insert control characters like line feeds using echo -e or printf.

The recommended way to compare a string is with either of these:

if [ "$VARIABLE" = "value" ]; then
if [[ $VARIABLE == value ]]; then

If you haven't already tried it, try using the newer [[, also known as extended test, instead of [, also known as the classic test.

http://wiki.bash-hackers.org/commands/classictest

http://wiki.bash-hackers.org/syntax/ccmd/conditional_expression

These are great resources to help you with getting further information if you want to know all the details about the test operators.