I just found and installed David Moore's libiptcdata with its iptc command-line utility. It's about the latter that my question is based.

The usage syntax is : iptc [OPTIONS] [FILE]...
where -m requires an IPTC field name, and -v is the value to assign or modify in that field. This value is a string bounded in double quotes. The thing I'm curious about (and as this little toy was written in 2005 I doubt Mr Moore is at his same email address as the one posted on his SourceForge manual page shows) is as follows:

How would one safely punctuate the value string, say, for a Caption or Special Instructions?

I've already tried an exclamation point, whereupon my bash shell reminded me that's a command in that shell (it noticed it even as it was in dbl-quotes). I suspect, then, that an alternate means of punctuation would have to be used. Having never installed or made any use of anything like this, I'm guessing it would either be the hex corresponding to the punctuation mark one wanted to represent, joined to the rest of the string by ampersand/s, or else an ampersand and another string containing the PM.
I suppose, also, that a hint or clue as to why would be in the C++ code in which this was written. Problem is, I don't know C++ well enough to know what to look for.

Could someone familiar with C++ coding download the libfiles (etc) and try to glean what the safer syntax would be to punctuate these strings [hex or &-signs between strings]?

Thanks for giving this a read.

BZT