test - set status according to condition

Test  evaluates  the  expression  expr.  If the value is true the exit status is null; otherwise the exit
       status is non-null.  If there are no arguments the exit status is non-null.

       The following primitives are used to construct expr.

       -rfile    True if the file exists (is accessible) and is readable.
       -wfile    True if the file exists and is writable.
       -xfile    True if the file exists and has execute permission.
       -efile    True if the file exists.
       -ffile    True if the file exists and is a plain file.
       -dfile    True if the file exists and is a directory.
       -sfile    True if the file exists and has a size greater than zero.
       -tfildes  True if the open file whose file descriptor number is fildes (1 by default) is the  same  file
                  as /dev/cons.
       -Afile    True if the file exists and is append-only.
       -Lfile    True if the file exists and is exclusive-use.
       -Tfile     True if the file exists and is temporary.
       s1=s2    True if the strings s1 and s2 are identical.
       s1!=s2   True if the strings s1 and s2 are not identical.
       s1         True if s1 is not the null string.  (Deprecated.)
       -ns1      True if the length of string s1 is non-zero.
       -zs1      True if the length of string s1 is zero.
       n1-eqn2  True  if  the  integers  n1 and n2 are arithmetically equal.  Any of the comparisons -ne, -gt,
                  -ge, -lt, or -le may be used in place of -eq.  The (nonstandard) construct -lstring,  meaning
                  the length of string, may be used in place of an integer.
       a-ntb    True if file a is newer than (modified after) file b.
       a-otb    True if file a is older than (modified before) file b.
       f-oldert True  if  file  f  is  older than (modified before) time t.  If t is a integer followed by the
                  letters y(years), M(months), d(days),  h(hours),  m(minutes),  or  s(seconds),  it  represents
                  current  time  minus  the  specified time.  If there is no letter, it represents seconds since
                  epoch.  You can also concatenate mixed units.  For example, 3d12h means three days and  twelve
                  hours ago.

       These primaries may be combined with the following operators:

       !         unary negation operator
       -o        binary or operator
       -a        binary and operator; higher precedence than -o(expr)  parentheses for grouping.

       The primitives -b, -u, -g, and -s return false; they are recognized for compatibility with POSIX.

       Notice that all the operators and flags are separate arguments to test.  Notice also that parentheses and
       equal signs are meaningful to rc and must be enclosed in quotes.

Test  is  a  dubious  way  to check for specific character strings: it uses a process to do what an rc(1)
       match or switch statement can do.  The first example is not only  inefficient  but  wrong,  because  test
       understands the purported string "-c" as an option.

              if (test $1 '=' "-c") echo OK # wrong!

       A better way is

              if (~ $1 -c) echo OK

       Test whether is in the current directory.

              test-fabc-o-dabc

       test - set status according to condition

rc(1)

                                                                                                    TEST(1plan9)

/src/cmd/test.c

testexpr