A single sentence in a man page doesn't stand alone. If you look at the SYNOPSIS section of the xargs man page on macOS you'll see:

Code:

SYNOPSIS
     xargs [-0opt] [-E eofstr] [-I replstr [-R replacements]] [-J replstr]
           [-L number] [-n number [-x]] [-P maxprocs] [-s size]
           [utility [argument ...]]

Every time you see "replstr" on this man page as underlined text, it will be referring to the option-argument given to a -I or a -J option. Every time you see "replacements" on this man page as underlined text, it will be referring to the option-argument to the -R option. As noted on the description of the -I option, if no -R option is present on the command line, the value of "replacements" defaults to 5.

In the command line:

Code:

cat fruits.txt | xargs -I {} echo "I like {}"

or the better command line (using fewer system resources, running faster, and producing the same output):

Code:

xargs -I {} echo "I like {}" < fruits.txt

there are two occurrences of the string {}: first occurrence is as the option-argument to the -I option and second is in the quoted argument to the echo command. With the -I {} option, each time {} appears (or occurs) in the command line arguments that xargs will be executing, it will be replaced by the contents of the current line of input read from standard input. So, if you get:

Code:

I like banana
I like apple
I like pear
...

from one of the above command lines, you'll get:

Code:

I like banana, I really like banana
I like apple, I really like apple
I like pear, I really like pear
...

from the command line:

Code:

xargs -I {} echo "I like {}, I really like {}" < fruits.txt

in other words, each occurrence of the -I option-argument in the command line arguments will be replaced by a copy of the current input line.

Does this help?