compare strings on Bash does not works

Question

is this correct?

    existed_design_document=$(curl "Administrator:*******@couchbase:8092/$MY_APP_DB_BUCKET/_design/dev_$environment" | jq '.error ')

    echo "$existed_design_document"
    if [ "$existed_design_document" == "not_found" ]
       then
         echo "The document design does not exist"
    fi

I see in the echo the value "not_found" but still I´m not getting into the if. Any idea why?

what's the output of declare -p existed_design_document or printf '%q\n' "$existed_design_document"? Like so you'll see if there are funny characters in your variable. echo is not reliable for this kind of inspections. — gniourf_gniourf
– gniourf_gniourf, Commented Oct 26, 2015 at 16:25
bash allows == inside [...], but it's good to get in the habit of using = instead (or use [[ ... == ... ]]). — chepner
– chepner, Commented Oct 26, 2015 at 16:34

Community · Accepted Answer · 2017-05-23 12:08:32Z

2

When I try with this baby example:

$ a=$(echo '{"error": "not_found"}' | jq .error)

I get:

$ declare -p a
declare -- a="\"not_found\""

So the quotes are also in the output of jq. So you need this:

if [[ $existed_design_document = "\"not_found\"" ]]

As @EtanReisner points out (thanks!): jq has the -r flag:

       With  this  option, if the filter´s result is a string then it will
       be written directly to standard output rather than being  formatted
       as a JSON string with quotes. This can be useful for making jq fil‐
       ters talk to non-JSON-based systems.

So you should even do this:

existed_design_document=$(curl "Administrator:*******@couchbase:8092/$MY_APP_DB_BUCKET/_design/dev_$environment" | jq -r .error)
echo "$existed_design_document"
if [[ $existed_design_document = "not_found" ]; then
     echo "The document design does not exist"
fi

edited May 23, 2017 at 12:08

CommunityBot

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answered Oct 26, 2015 at 16:29

gniourf_gniourf

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2 Comments

Etan Reisner Over a year ago

The jq flag -r would also be useful here.

gniourf_gniourf Over a year ago

@EtanReisner Oh cool! (I didn't even read jq's man page, just answered from obvious facts… but will edit the answer).

user2350426 · Accepted Answer · 2015-10-26 22:50:46Z

0

One more reliable solution that is not affected by quotes, but only looks for a given string is based on regex. This will match your text:

if [[ $existed_design_document =~ not_found ]]; then
     echo "The document design does not exist"
fi

That will match anything that contain not_found, so, it is more flexible, but also could match some UN-expected strings. It is a trade-off between flexibility and precision.

answered Oct 26, 2015 at 22:50

user2350426

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