[examples/cat] Add cat example.

examples/cat.lua

@@ -0,0 +1,78 @@
+#!/bin/env lua
+-- Trimmed down cat(1) utility.
+--
+-- Concatenate files to stdout, making sure bytes are actually written
+-- out successfully.
+--
+-- SYNOPSIS:
+-- cat.lua [-u] <FILES...>
+--
+-- NOTE: utility doesn't explicitly allow to concatenate stdin.
+local osx = require 'osx'
+local io = require 'io'
+
+local uflag = false
+
+local function cat(path)
+    local ferr = io.stderr
+
+    local f, err = io.open(path, 'r')
+    if err then
+        ferr:write(err, "\n")
+        return false
+    end
+
+    local success = true  -- unless it happens to be a failure
+    local fout = io.stdout
+
+    while true do
+        local buf, err = f:read(4096)
+        if err then
+            ferr:write(err, "\n")
+            success = false
+        end
+        if not buf then
+            break  -- done with file
+        end
+        assert(fout:write(buf))
+    end
+    f:close()
+
+    assert(fout:flush())
+    if not osx.isatty(fout) then
+        assert(osx.commit(fout))
+    end
+    return success
+end
+
+local function parseargs(...)
+    local files = {}
+    for i = 1, select('#', ...) do
+        local arg = select(i, ...)
+        if arg == '-u' then
+            uflag = true
+        else
+            files[#files+1] = arg
+        end
+    end
+    if #files == 0 then
+        error("Missing file arguments")
+    end
+    return files
+end
+
+local files = parseargs(...)
+
+io.stdout:setvbuf(uflag and 'no' or 'full')
+
+local success = true
+for _, path in ipairs(files) do
+    if not cat(path) then
+        success = false
+    end
+end
+
+if not success then
+    os.exit(1)
+end
+