Bash string comparision [duplicate]

Question

Please help.

I'm trying to compare string1 against string2 in a Bash script.

I can do the easy bit of:-

if [[ $string1 == $string2 ]]
then    
    yippee    
fi

What I'm having trouble with is the syntax for when

"the$string1" == $string2  or "a$string1" == $string2

or

 $string1 == the$string2 or $string1 == a$string2

I assume it's something like:-

if [[ $string1 == $string2 || "(a|the)$string1" == $string2 || $string1 == "(a|the)$string2" ]]

But it's not and I cannot seem to find the answer. (I'm obviously asking the wrong question!)

Thanks for any help.

PS I'd rather not use any external progs such as awk etc.

Can you provide some concrete examples of comparisons that should be considered equal and not equal? Do you just want to compare the two strings ignoring any leading a or the? — chepner
– chepner, Commented Mar 24, 2020 at 15:41
Possible duplicates stackoverflow.com/questions/19441521/bash-regex-operator stackoverflow.com/questions/18709962/… stackoverflow.com/questions/17420994/… — oguz ismail
– oguz ismail, Commented Mar 24, 2020 at 15:46

glenn jackman · Accepted Answer · 2020-03-24 15:44:20Z

0

You might want:

if [[ $string1 == *"$string2"* ]]; then
    echo "string1 contains string2"

elif [[ $string2 == *"$string1"* ]]; then
    echo "string2 contains string1"
fi

Within [[...]] the == operator is a pattern matching operator.

Ref: 6.4 Bash Conditional Expressions

For specifically an optional "a" or "the" prefix:

[[ $string1 == ?(a|the)"$string2" || $string2 == ?(a|the)"$string1" ]]

That uses bash's extended patterns, see 3.5.8.1 Pattern Matching

answered Mar 24, 2020 at 15:44

glenn jackman

249k42 gold badges233 silver badges362 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

glenn jackman Over a year ago

Note that the variable on the right-hand side is quoted: that is to treat it as literal text, in case the variable's contents contain shell globbing characters.

Collectives™ on Stack Overflow

Bash string comparision [duplicate]

1 Answer 1

1 Comment

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Linked

Related