Succor in September 2023, we extended the curl present line instrument with a brand aloof moderately evolved and versatile variable gadget. Using this, users can use recordsdata, atmosphere variables and more in a highly effective way when constructing curl present traces in ways no longer beforehand doable – with practically all original present line alternatives.
curl present traces were already reasonably succesful sooner than this, however these aloof variables absolutely took it up several additional notches.
Come February 2025
In the pending curl 8.12.0 release, we extend this variable increase a puny little bit of additional. Beginning now, you might per chance put a variable to defend the contents of a partial file. Win a byte differ from a given file precise into a variable and use that variable within the present line, barely than the utilization of the total file.
You’re going to salvage the first few bytes and use as a username, you might per chance salvage a hundred bytes within the heart of a file and POST that or dwell endless assorted things.
Byte differ
You demand curl to learn a byte differ from a file barely than the total one by appending ;[n-M] to the filename, when you happen to put a variable. Where N and M are the first and the final byte offsets into the file, 0 being the first byte. Whenever you happen to tear over the 2nd number, it approach unless the stop of file.
As an instance, salvage the first 32 bytes from a file named secret and map as password for daniel:
curl --variable "pwd@secret;[0-31]"
--assign bigger-person daniel:{{pwd}}
https://instance.com/
Skip the first thousand bytes from a file named localfile and ship the remainder of it in a POST:
curl --variable "upload@localfile;[1000-]"
--assign bigger-submit '{{upload}}'
https://instance.com/
With functions
You might per chance pointless to divulge additionally mix the byte offsets with the ordinary assign bigger functions. As an instance, salvage the first hundred bytes from the file called random and ship them execrable64 encoded in a POST:
curl --variable "binary@random;[0-99]"
--assign bigger-submit '{{binary:b64}}'
https://instance.com/
I hope you will cherish it.
Update
After his submit became first published, now we have discussed the proper syntax for this option and have determined to tweak it a puny little bit of to assign it much less doubtless that old curl variations might per chance well also simply be tricked when making an strive a brand aloof present line alternatives. I will change this blog submit accordingly once the aloof syntax has landed.
