docs: add 'Use Unix line endings in Unix tools' post

source/_posts/unix-tools-line-endings.md

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+---
+title: Use Unix line endings in Unix tools
+date: 2018-11-08 00:00:00
+tags:
+---
+
+Before you use any Unix tools to process some file, make sure the file only use Unix [line endings](https://en.wikipedia.org/wiki/Newline#Representation).
+
+<!-- more -->
+
+Note that many text files you downloaded most probably use Windows line endings.
+
+To [recap](https://en.wikipedia.org/wiki/Newline#Representation),
+
+Type | Line ending | Escape sequence
+---|--- | ---
+Windows | CR LF | \r\n
+Unix (including Linux distro, *BSD and macOS) | LF | \n
+Classic Mac OS (i.e. Mac OS 9 or older) | CR | \r
+
+Unix tools, regardless from Busy/ToyBox, GNU or BSD, only support Unix line endings. 
+
+So, before you use any of them, make sure you convert the file to Unix line endings, especially before `grep -f`.
+
+Use `dos2unix`  to convert from Windows to Unix line endings, e.g.
+
+```
+# STDIN to STDOUT
+cat input | dos2unix
+# STDIN to FILE
+cat input | dos2unix > output
+# Convert and replace current file
+dos2unix filename
+```
+
+If your distro includes BusyBox (e.g. Ubuntu), use `busybox dos2unix`.