add string slices

teststrings

@@ -0,0 +1,80 @@
+x=string0
+y=$(x)
+# $(x) $(y)
+
+x="string1"
+y=$(x)
+# $(x) $(y)
+
+x="'string2'"
+y=$(x)
+# $(x) $(y)
+
+x='"string3"'
+y=$(x)
+# $(x) $(y)
+
+x=\"string4\"
+y=$(x)
+# $(x) $(y)
+
+x=\'string5\'
+y=$(x)
+# $(x) $(y)
+
+x="Hello World"[2:8]
+# $(x) should be: llo Wo
+
+x=Hello World[2:8]
+# "$(x)" should be: "Hello World[2:8]"
+
+x="Hello World"[2,3]
+# $(x) should be: llo
+
+x="Hello World"[1]
+# $(x) should be: e
+
+x="Hello World"[-1]
+# $(x) should be: d
+
+x="Hello World"[-2:]
+# $(x) should be: ld
+
+x="Hello World"[-2,6]
+# $(x) should be: ld
+
+x="Hello World"[1:1000]
+# $(x) should be: ello World
+
+x="Hello World"[1:-1000]
+# "$(x)" should be: ""
+
+x="Hello World"[:]
+# "$(x)" should be: "Hello World"
+
+x="Hello World"[1?6:0:]
+# "$(x)" should be: "World"
+
+x="Hello World"[1000]
+# "$(x)" should be: ""
+
+x="Hello World"[-1000]
+# "$(x)" should be: ""
+
+x="Hello World"[-1000,1005]
+# "$(x)" should be: "World"
+
+x="Hello World"[-1000:5]
+# "$(x)" should be: "World"
+
+x="Hello World"[7:4]
+# "$(x)" should be: ""
+
+x="Hello World"[1?3+4:0:7-8]
+# "$(x)" should be: "orl"
+
+x="Hello World"[7,-1]
+# "$(x)" should be: ""
+
+x='\"\\x'[2]
+# $(x) should be: x