September 2017 Update

Task/Binary-strings/Jq/binary-strings-2.jq

@@ -0,0 +1,70 @@
+## Creation of an entity representing an empty binary string
+
+[]
+
+## Assignment
+
+# Unless a check is appropriate, assignment can be done in the
+# usual ways, for example:
+
+[0] as $x    # assignment to a variable, $x
+
+s as $x      # assignment of s to a variable
+
+.key = s     # assignment to a key in a JSON object
+
+# If s must be checked, these become:
+
+(s|check_binary) as $x
+
+.key = (s|check_binary)
+
+## Concatenation:
+
+str+str2
+
+## Comparison
+
+[72,101,108,108,111] == ("Hello"|explode)  # evaluates to true
+
+# Other jq comparison operators (!=, <, >, <=, >=) can be used as well.
+
+## Cloning and copying
+# In jq, all entities are immutable and so the distinction between
+# copying and cloning is irrelevant in jq.
+# For example, consider the expression "$s[0] = 1"
+# in the following:
+
+[0] as $s | $s[0] = 1 | $s
+
+# The result is [0] because the expression "$s[0] = 1"
+# evaluates to [1] but does not alter $s.  The value of
+# $s can be changed by assignment, e.g.
+
+[0] as $s | $s[0] = 1 | . as $s
+
+## Check if an entity represents the empty binary string
+
+length == 0
+# or
+s == []
+
+## append a byte, b
+
+s + [b]                 # if the byte, b, is known to be in range
+s + ([b]|check_binary)  # if b is suspect
+
+## Extract a substring from a string
+
+# jq uses an index origin of 0 for both JSON arrays strings,
+# so to extract the substring with indices from m to (n-1)
+# inclusive, the expression s[m:n] can be used.
+
+# There are many other possibilities, such as s[m:], s[-1], etc.
+
+## Replace every occurrence of one byte, x, with
+## another sequence of bytes presented as an array, a,
+## of byte-valued integers:
+
+reduce .[] as $byte ([];
+  if $byte == x then . + a else . + [$byte] end)