From The Collaborative International Dictionary of English v.0.48 :
1 \1\ adj.
1. used of a single unit or thing; not two or more; --
representing the number one as an Arabic numeral.
Syn: one, i, ane
[WordNet 1.5 +PJC]
From The Free On-line Dictionary of Computing (30 December 2018) :
$1
The first positional parameter in shell
programming and related languages. Occurrences of $1 are
replaced by the first actual argument provided by the user
when the shell script is run. $2 is replaced by the second
argument, and so on up to $9.
You may have arrived at this entry by following a URL like
"http://foldoc.org?$1", which is actually a template used to
generate pointers to FOLDOC definitions by replacing "$1" with
the term to be defined, e.g. in a wiki interwiki map.
(2006-09-10)