Add a prefix and a suffix to a string

[NikosAlexandris]

How can one simply add a prefix and a suffix to a string, using put and gsub or else ssub?

I am trying something like

put -S '$v=ssub($v,"^([^_].*)","_$v")'

for adding a _ as a prefix, but it obviously does not work.

[NikosAlexandris]

The following works:

then put -S '$v=sub($v,"^","`")' then put -S '$v=sub($v,"$","`")'

But, I can't seem to make a single call out of it... 🤷🏼

[NikosAlexandris]

Indeed, I am interested in an mlr solution using sub or gsub or ssub.

In this case all input data are strings -- but, thank you, I will keep it in mind to check for the data type.
And, why not including the _SUFF in the sub example? I.e. how to do prefix and suffix in one step using sub?

[aborruso]

And, why not including the _SUFF in the sub example? I.e. how to do prefix and suffix in one step using sub?

What about using regex syntax

Running echo 'a=hello' | mlr put -S '$a=sub($a,"^(.+)$","PRE_"."\1"."_SUFF")' you will have a=PRE_hello_SUFF

[NikosAlexandris]

Thanks @aborruso -- I was looking for this! put -S '$v=sub($v,"^(.+)$",""."\1"."")' (for me and also for aborruso/millerQuestions@8a4a47f#diff-27033d9dd92fa04ad7a610845e3354c61fc8ce5fe2abd7c35c17c260cd16e2adR23).

[NikosAlexandris]

And, why not including the _SUFF in the sub example? I.e. how to do prefix and suffix in one step using sub?

What about using regex syntax

Running echo 'a=hello' | mlr put -S '$a=sub($a,"^(.+)$","PRE_"."\1"."_SUFF")' you will have a=PRE_hello_SUFF

Can you please put it in a separate answer, so I can mark it as answered?

[trantor]

In this case all input data are strings -- but, thank you, I will keep it in mind to check for the data type.
And, why not including the _SUFF in the sub example? I.e. how to do prefix and suffix in one step using sub?

Well @NikosAlexandris , I was merely referring to your example using the start of pattern anchor. I thought that you might have had some additional trouble since, as @aborruso showed, the string substitution is rather similar to your average awk or similar, with \0 \1 and the likes as back-references.

There's an example of the back-reference expansion here in passing, however the whole regex topic is not exactly explained in detail in the docs. That might be something to improve upon for the new release @johnkerl .
My bad, here it is

Anyway @aborruso a (imho) better answer in this case is

$ echo 'a=hello' | mlr put -S '$a=sub($a,".*","PRE_\0_SUFF")'
a=PRE_hello_SUFF

No needless concatenation operators, no unnecessary capture group.

[aborruso]

And, why not including the _SUFF in the sub example? I.e. how to do prefix and suffix in one step using sub?

What about using regex syntax

Running echo 'a=hello' | mlr put -S '$a=sub($a,"^(.+)$","PRE_"."\1"."_SUFF")' you will have a=PRE_hello_SUFF

[johnkerl]

@NikosAlexandris can you show some sample input and desired output? At present I think you can do $v = "prefix" . $v . "suffix" but maybe I misunderstand the question ...

[NikosAlexandris]

@johnkerl This is happening here: https://github.com/aborruso/millerQuestions/blob/8b77f635d6a25191342892dcc141c48dcdc9e07b/script/millerQuestions.sh#L23 with input from https://github.com/aborruso/millerQuestions/blob/8b77f635d6a25191342892dcc141c48dcdc9e07b/data/millerQuestions.yml#L1-L5 for example.

[NikosAlexandris]

Thank you @johnkerl! Way easier and readable... Will update the script.