Implement read -n, and a placeholder for -r.

Addresses issue #26.

core/builtin.py

@@ -365,12 +365,32 @@ def Jobs(argv, job_state):
   return 0
 
 
+READ_SPEC = _Register('read')
+READ_SPEC.ShortFlag('-r')
+READ_SPEC.ShortFlag('-n', args.Int)
+
 def Read(argv, mem):
   # TODO:
-  # - parse flags.
   # - Use IFS instead of Python's split().
 
-  names = argv
+  arg, i = READ_SPEC.Parse(argv)
+
+  if not arg.r:
+    util.warn('*** read without -r not implemented ***')
+
+  names = argv[i:]
+  if arg.n is not None:
+    try:
+      name = names[0]
+    except IndexError:
+      name = 'REPLY'  # default variable name
+    s = os.read(sys.stdin.fileno(), arg.n)
+    #log('read -n: %s = %s', name, s)
+
+    state.SetLocalString(mem, name, s)
+    # NOTE: Even if we don't get n bytes back, there is no error?
+    return 0
+
   line = sys.stdin.readline()
   if not line:  # EOF
     return 1
@@ -387,11 +407,13 @@ def Read(argv, mem):
 
   strs = line.split(None, n-1)
 
+  # TODO: Use REPLY variable here too?
   for i in xrange(n):
     try:
       s = strs[i]
     except IndexError:
       s = ''  # if there are too many variables
+    #log('read: %s = %s', names[i], s)
     state.SetLocalString(mem, names[i], s)
 
   return status

gold/nix.sh

@@ -0,0 +1,32 @@
+#!/bin/bash
+#
+# Usage:
+#   ./nix.sh <function name>
+
+set -o nounset
+set -o pipefail
+set -o errexit
+
+# My simpler rewrite.
+isElfSimple() {
+  local path=$1  # double quotes never necessary on RHS
+  local magic
+
+  # read 4 bytes from $path, without escaping, into $magic var
+  read -r -n 4 magic < "$path"
+
+  # Return the exit code of [[
+  [[ "$magic" =~ ELF ]]
+}
+
+isElfSimpleWithStdin() {
+  seq 3 > /tmp/3.txt
+  while read line; do
+    echo $line
+    isElfSimple /bin/true && echo YES
+    isElfSimple $0 || echo NO
+    echo
+  done < /tmp/3.txt
+}
+
+"$@"

spec/builtins.test.sh

@@ -202,6 +202,18 @@ echo /$x/$y/$z/
 umask | grep '[0-9]\+'  # check for digits
 # status: 0
 
+### Read -n (with $REPLY)
+echo 12345 > $TMP/readn.txt
+read -n 4 x < $TMP/readn.txt
+read -n 2 < $TMP/readn.txt  # Do it again with no variable
+argv.py $x $REPLY
+# stdout: ['1234', '12']
+# N-I dash stdout: []
+
+### get umask
+umask | grep '[0-9]\+'  # check for digits
+# status: 0
+
 ### set umask in octal
 rm $TMP/umask-one $TMP/umask-two
 umask 0002

test/gold.sh

@@ -92,6 +92,10 @@ glob() {
   _compare gold/glob.sh
 }
 
+nix() {
+  _compare gold/nix.sh isElfSimpleWithStdin
+}
+
 all() {
   version-text
   count