Added Tee commands

tail_less_cat_head.md

@@ -1,4 +1,4 @@
-# <a name="cat-less-tail-and-head"></a>Cat, Less, Tail and Head
+# <a name="cat--tail-and-head"></a>Cat, Less, Tail, Head and Tee
 
 **Table of Contents**
 
@@ -27,6 +27,14 @@
     * [combining head and tail](#combining-head-and-tail)
     * [Further Reading for head](#further-reading-for-head)
 * [Text Editors](#text-editors)
+* [Tee](#Tee)
+    * [Write output to stdout, and also to a file](#output-to-stdout)
+    * [Write the output to two commands](#output-to-two-commands)
+    * [Misc Tee Command Operations](#Misc)
+
+
+
+
 
 <br>
 
@@ -680,3 +688,39 @@ Powerful text editors
 * [sublime](https://www.sublimetext.com/)
 
 Check out [this analysis](https://github.com/jhallen/joes-sandbox/tree/master/editor-perf) for some performance/feature comparisons of various text editors
+
+
+## <a name="Tee"></a>Tee
+
+### <a name="output-to-stdout"></a>Write output to stdout, and also to a file
+```
+  The following command displays output only on the screen (stdout).
+      $ ls 
+
+  The following command writes the output only to the file and not to the screen.
+      $ ls > file
+
+  The following command (with the help of tee command) writes the output both to the screen (stdout) and to the file.
+      $ ls | tee file
+```
+
+### <a name="output-to-two-commands"></a>Write the output to two commands
+```
+   You can also use tee command to store the output of a command to a file and redirect the same output as an input to another   command.
+
+   The following command will take a backup of the crontab entries, and pass the crontab entries as an input to sed command which will do the substituion. After the substitution, it will be added as a new cron job.
+
+      $ crontab -l | tee crontab-backup.txt | sed 's/old/new/' | crontab –
+```
+
+### <a name="Misc"></a>Misc Tee Command Operations
+```
+   By default tee command overwrites the file. You can instruct tee command to append to the file using the option –a as shown below.
+
+      $ ls | tee –a file
+
+   You can also write the output to multiple files as shown below.
+
+      $ ls | tee file1 file2 file3
+
+```