Problems getting relatively simple regex to match in a bash script

Question

I'm reasonably proficient with regexes, but I'm having trouble with doing something simple in a Bash script.

I'm working with the following script excerpt:

    if [[ "$message" =~ "^The node was low on resource: ephemeral-storage.*$" ]]; then
        message="ephemeral storage"
    elif [[ "$message" =~ "^The node was low on resource: memory.*$" ]]; then
         message="memory"
    elif [[ "$message =~ ^The node was low on resource: \[DiskPressure\].*$" ]]; then
         message="disk"
    else
        echo "No match"
    fi

If the value in "message" begins with "The node was low on resource: ephemeral-storage. Container ...", this matches the LAST expression. I've been staring at this for quite a while, and I'm just not getting it.

I turned on verbose mode in the script, and I see the following in the output:

+ [[ The node was low on resource: ephemeral-storage. Container ...  =~ \^The node was low on resource: ephemeral-storage\.\*\$ ]]
+ [[ The node was low on resource: ephemeral-storage. Container ...  =~ \^The node was low on resource: memory\.\*\$ ]]
+ [[ -n The node was low on resource: ephemeral-storage. Container ...  =~ ^The node was low on resource: \[DiskPressure\].*$ ]]
+ message=disk

Note two things in this output. I'm eliding much of the value that's in the "message" variable with "...". Second, I see the "-n" on the output from the last elif. Clearly, that's not in my code, not explicitly. Checking the docs, I see the "-n" operator returns true if the string operand length is non-zero. So, if that's the code that's being executed, I can see why it's considering the last condition to be true, but I don't understand what it's doing here.

anubhava · Accepted Answer · 2020-04-27 18:39:42Z

1

Regex must not be quoted in BASH. However you can just use glob matching instead of regex:

case $message in
   "The node was low on resource: ephemeral-storage"*)
   message="ephemeral storage";;
   "The node was low on resource: memory"*)
   message="memory";;
   "The node was low on resource: [DiskPressure]"*)
   message="disk";;
   *)
   echo "No match";;
esac

edited Apr 27, 2020 at 18:39

answered Apr 27, 2020 at 18:35

anubhava

790k67 gold badges603 silver badges671 bronze badges

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

1 Comment

Michaël Le Barbier Over a year ago

If so it would be much easier to read to use a case/esac instead of this java-esque horror.

Philippe · Accepted Answer · 2020-04-27 19:00:12Z

0

It would be much easier if regex patterns are defined in variables :

message="The node was low on resource: ephemeral-storage. Container"

p_ephemeral='^The node was low on resource: ephemeral-storage.*$'
p_memory='^The node was low on resource: memory.*$'
p_disk='^The node was low on resource: \[DiskPressure\].*$'

if  [[ "$message" =~ $p_ephemeral ]]; then
    message="ephemeral storage"
elif [[ "$message" =~ $p_memory ]]; then
    message="memory"
elif [[ "$message" =~ $p_disk ]]; then
    message="disk"
else
   echo "No match"
fi

answered Apr 27, 2020 at 19:00

Philippe

27.7k4 gold badges28 silver badges45 bronze badges

Collectives™ on Stack Overflow

Problems getting relatively simple regex to match in a bash script

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related