concat - Man Page

concat ?arg arg ...?

This command joins each of its arguments together with spaces after trimming leading and trailing white-space from each of them.  If all of the arguments are lists, this has the same effect as concatenating them into a single list. Arguments that are empty (after trimming) are ignored entirely. It permits any number of arguments; if no args are supplied, the result is an empty string.

Although concat will concatenate lists, flattening them in the process (so giving the following interactive session):

% concat a b {c d e} {f {g h}}
a b c d e f {g h}

it will also concatenate things that are not lists, as can be seen from this session:

% concat " a b {c   " d "  e} f"
a b {c d e} f

Note also that the concatenation does not remove spaces from the middle of values, as can be seen here:

% concat "a   b   c" { d e f }
a   b   c d e f

(i.e., there are three spaces between each of the a, the b and the c).

append(n), eval(n), join(n)

concatenate, join, list

after(n), append(n), eval(n).