add Dockerfile

Dockerfile

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+FROM alpine
+MAINTAINER Shamil Ganiev <samolander@yandex.ru>
+
+WORKDIR /srv
+
+COPY cmd.sh /usr/bin
+
+RUN apk add --no-cache optipng bash git \
+    && echo 'PS1="\[\e[1;32m\][\u@\h \[\e[1;34m\]\W \[\e[1;32m\]]\[\033[00m\] "' > /root/.bashrc 
+
+CMD [ "cmd.sh" ]

cmd.sh

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+#!/usr/bin/env bash
+
+modified_files=`git diff --cached --name-only | grep .png`
+current_dir=`pwd`
+echo $modified_files
+if [ -z "$modified_files" ];then
+  exit 0
+else
+  for i in ${modified_files}; do optipng -o7 -quiet  ${i}; done
+fi
+