How to parse a path with regex - optional fields

Question

I am using the following regex: (example here: https://regex101.com/r/dVTUrM/1)

\/(?<field1>.{4})\/(?<field2>.*?)\/(?<field3>.*?)\/(?<field4>.*?)\/(?<field5>.*?)\/(?<field6>.*)

to parse the following text:

pyramid:/A49E/18DA-6FAB-4921-8AEB-45A07B162DA5/{E3646FA1-4652-45E9-885A-3756FC574057}/{F1864679-1D9D-4084-B38D-231D793AA15D}/9/abc.tif

giving the following result:

Group `field1`  9-13    `A49E`
Group `field2`  14-46   `18DA-6FAB-4921-8AEB-45A07B162DA5`
Group `field3`  47-85   `{E3646FA1-4652-45E9-885A-3756FC574057}`
Group `field4`  86-124  `{F1864679-1D9D-4084-B38D-231D793AA15D}`
Group `field5`  125-126 `9`
Group `field6`  127-134 `abc.tif`

But if field5 and field 6 are missing:

pyramid:/A49E/18DA-6FAB-4921-8AEB-45A07B162DA5/{E3646FA1-4652-45E9-885A-3756FC574057}/{F1864679-1D9D-4084-B38D-231D793AA15D}

I would like this to work and for field5 and field6 to be blank.

Is this possible by modifying the regex statement?

Note: only field6 may be missing as well.

Can you put non-capturing parentheses around the optional bits, and a ? qualifier? That is, use …/(?:(?<field5>.*?)(?:\/(?<field6>.*))?)? at the end… Or some variant on this. You might need to review the greediness of field 6. — Jonathan Leffler
– Jonathan Leffler, Commented Mar 8, 2017 at 20:16

Joey · Accepted Answer · 2017-03-08 20:38:54Z

1

Here you go:

(?x)^pyramid:
/(?P<field1>[^/]{4})
/(?P<field2>[^/]+)
/(?P<field3>[^/]+)
/(?P<field4>[^/]+)
(?:
    /(?P<field5>[^/]+)
    /(?P<field6>[^/]+)
)?

See a demo on regex101.com.

Or, in short (without the verbose flag):

^pyramid:/(?P<field1>[^/]{4})/(?P<field2>[^/]+)/(?P<field3>[^/]+)/(?P<field4>[^/]+)(?:/(?P<field5>[^/]+)/(?P<field6>[^/]+))?

Depending on the programming language / flavour used, you might use other delimiters like ~ so that you don't need to escape the forward slashes anymore. The (?: ... ) construct is a non capturing group which is made optional with ? to allow 4 or 6 (but not five!) fields.

edited Mar 8, 2017 at 20:38

Joey

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answered Mar 8, 2017 at 20:19

Jan

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5 Comments

Jordan Running Over a year ago

Why not drop the x flag and use [^/] instead of [^/\r\n]?

Jan Over a year ago

@Jordan: You're absolutely right, just copied it from regex101.com and the newline was there to illustrate the different lines though they're not needed in the actual expression.

Jan Over a year ago

@Jordan: Updated to reflect your thoughts.

Brian Rice Over a year ago

I updated it to this: regex101.com/r/y1kfox/2 as field6 can be missing or field5 and field6 can be missing... and also the word pyramid can be any string value.

Brian Rice Over a year ago

Ok... not sure why I was having trouble... but this works with my modifications and yours. regex101.com/r/y1kfox/3

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