what is '/[A-Z]/ s| |/|gp' meaning?

Question

I am reading a sed tutorial at https://riptutorial.com/sed/example/13753/lines-matching-regular-expression-pattern.

Looks like

$ sed -n '/[A-Z]/ s| |/|gp' ip.txt

is filtering 'Add Sub Mul Div' out of the file, and convert it to 'Add/Sub/Mul/Div'

I really don't understand the regex considering I just read https://www.tldp.org/LDP/abs/html/x23170.html.

It does not even match the print syntax which is:

[address-range]/p

and is the pipe sign '|' here alternation?

Could anyone explain:

'/[A-Z]/ s| |/|gp'

in English?

Edit

I also found that the extra empty space before 's' and after '/' is allowed and does not do anything. the correct syntax should be:

[address-range]/s/pattern1/pattern2/

the syntax check of sed pattern is not strict, and confusing

Answer 1

• -n option turns off automatic printing
• sed allows to qualify commands with an address filtering, which could be regex or line addresses
  • for example, /foo/ d will delete lines containing foo
  • and /foo/ s/baz/123/ will change baz to 123 only if the line also contains foo
• /[A-Z]/ match only lines containing at least one uppercase alphabet
  • if such a line is matched:
  • s| |/|gp perform this substitution and print
  • s command allows delimiter other than / too (see Using different delimiters in sed commands and range addresses)
  • in this case, using | allows you to use / as a normal character instead of having to escape it