~ $ mkdir tmp 
~ $ cd tmp 
~/tmp $ mkdir a 
~/tmp $ cd a 
~/tmp/a $ mkdir b 
~/tmp/a $ cd b 
~/tmp/a/b/ $ mkdir c 
~/tmp/a/b/ $ cd c 
~/tmp/a/b/c $ 

mkdir -p tmp/a/b/c 

cp a.tar.gz /tmp 
cd /tmp 
tar xzvf a.tar.gz 

tar xzvf -C /tmp a.tar.gz 

cat a.txt | grep "a" 

grep "a" a.txt 

cat a.txt | grep "a" | wc -l 

grep -c "a" a.txt 

~/tmp $ ls -l /tmp| grep Dec 
-rw-r--r-- 7 joe joe 12043 Jan 27 20:36 December_Report.pdf 
-rw-r--r-- 1 root root 238 Dec 03 08:19 README 
-rw-r--r-- 3 joe joe  5096 Dec 14 14:26 archive.tar 
~/tmp $ 

~/tmp $ ls -l | awk '$6 == "Dec"' 
-rw-r--r-- 3 joe joe  5096 Dec 14 14:26 archive.tar 
-rw-r--r-- 1 root root 238 Dec 03 08:19 README 
~/tmp $