How to check if string exists in bash variable

user_16109956 0
Viewed 131

I have a variable $FOO with values one two three.

echo $FOO
one two three

Is there a way in bash to check if two exists and exactly matches one of the values of $FOO

I can do this

if [[ "two" =~ ^(one|two|three)$ ]]; then
    echo "two is in the list"
else
    echo "two is not in the list"
fi

And it works, but I'd like to check using the actual variable $FOO and not (one|two|three)$

Is this possible?

variables bash string
7 Answers

If the items in $FOO are guaranteed to be separated by spaces, you can use this:

if [[ " $FOO " = *" $TWO "* ]]; then
    ...

Note that this reverses the roles of $FOO and $TWO from what you might expect; it treats $FOO as the string to check against a pattern, and the pattern is essentially "something that contains $TWO". It also adds explicit spaces to $TWO to make sure it matches only full items, and similarly adds spaces around $FOO so that'll match the first and last items in it.

If the delimiters in $FOO might be tabs or other space-like characters, you can use this more complex pattern:

if [[ " $FOO " = *[[:space:]]"$TWO"[[:space:]]* ]]; then
user_898170

Heres how to do it below

FOO='one two three'
TWO='two'
if [[ "$FOO" == *"$TWO"* ]]; then
  echo "two is in the list"
fi

wildcard aka * is a symbol used to represent zero, one or more characters.

user_170289700

Using an array

$ FOO=(one two three)
$ n=0;while [[ $n -lt ${#FOO} ]]; do  [[ "${FOO[$n]}" == "two" ]] && echo "two is in the list"; n=$(( $n + 1 )); done
two is in the list
user_163721090

You can construct pattern with :

foo=(one two three)
pattern="^($(IFS="|"; echo "${foo[*]}"))\$"

if  [[ two =~ $pattern ]]; then
    echo "two is in the list"
else
    echo "two is not in the list"
fi
user_21256710

It's odd that nobody posted case. It's the simplest and most portable. Notice the added spaces around $FOO.

case " $FOO " in
*" two "*) echo two is in the list; ;;
*) echo two is not in the list; ;;
esac
user_90727530

You can try something like this

FOO="one two three"

foo=( $FOO )

if [[ "${foo[*]}" =~ ' two ' ]]
then
    echo "two is in the list"
else
    echo "two is not in the list"
fi

which will work for the simple cases (i.e. no spaces in the values)

user_2364650

This should also work for you.

FOO='one two three'
TWO='two'
if [[ "$FOO" =~ "$TWO"( |$) ]]
then
  echo "two is in the list"
else
    echo "two is not in the list"
fi

This will give an exact pattern match.

user_124255640
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