add isdiff

diff --git a/isdiff b/isdiff
new file mode 100755 (executable)
index 0000000..cb6f85f
--- /dev/null
+++ b/isdiff
@@ -0,0 +1,70 @@
+#!/bin/bash
+# Copyright (C) 2014 Ian Kelling
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+isdiff() {
+    local help="Usage: isdiff [--help|-h] [-v] [-x] FILE1 FILE2
+Test if FILE1 and FILE2 have the same contents
+
+Returns 0 for same, 1 for diff, 2 for error.
+
+-v   verbose
+-r   use most reliable checksum available, ie. sha instead of md5"
+
+    local v x y reliable
+    while true; do
+        if [[ $1 == --help ]]  || [[ $1 == -[^-]* && $1 == *h* ]]; then
+            echo "$help"
+            return
+        elif [[ $1 == -[^-]* && $1 == *v* ]]; then
+            v=true
+            shift
+        elif [[ $1 == -[^-]* && $1 == *r* ]]; then
+            reliable=true
+            shift
+        else
+            break
+        fi
+    done
+
+    x=($(type -p sha512sum) $(type -p sha256sum) $(type -p sha1sum) $(type -p md5sum))
+    if [[ $reliable ]]; then
+        sumbinary=$x
+    else
+        sumbinary=${x[${#x[@]}-1]}
+    fi
+
+    [[ $sumbinary ]] || {
+       echo "Need 1 of sha512sum sha256sum sha1sum or md5sum for sum() function"
+       return 1
+    }
+    if [[ $# != 2 ]]; then
+       [[ $v ]] && echo Error: need 2 arguments.
+       return 2
+    fi
+    if [[ $v ]]; then
+       x=$($sumbinary < "$1" ) || return 2
+       y=$($sumbinary < "$2" ) || return 2
+    else
+       { x=$($sumbinary < "$1" ) ;} 2>/dev/null || return 2
+       { y=$($sumbinary < "$2" ) ;} 2>/dev/null || return 2
+    fi
+    if [[  $x == "$y" ]]; then
+       return 1 # same
+    else
+       [[ $v ]] && echo "$1" "$2" different.
+       return 0
+    fi
+}
+isdiff "$@"