16.4.3 Relations for expr

expr supports the usual logical connectives and relations. These are higher precedence than either the string or numeric operators (previous sections). Here is the list, lowest-precedence operator first.

`|'

Returns its first argument if that is neither null nor 0, otherwise its second argument.

`&'

Return its first argument if neither argument is null or 0, otherwise 0.

`< <= = == != >= >'

Compare the arguments and return 1 if the relation is true, 0 otherwise. == is a synonym for =. expr first tries to convert both arguments to numbers and do a numeric comparison; if either conversion fails, it does a lexicographic comparison using the character collating sequence specified by the LC_COLLATE locale.