Unix essentials

1. Remove starting and ending " ( double quotes ) in a word
      sed -e 's/^"//' -e 's/"$//'  -- And for Remove all " use sed -e 's/"//g'
2. Remove carriage return and new lines
      | tr -d '\n'   and \r for carriage return
3. Second word after = is : awk -F '=' '{print $2}'
4. Host name to a variable : hname=$(hostname)
5. CURRENTDATE="$(date +%Y%m%d%H%M%S)"
6. if [ $# -ne 1 ] -- Number of arguments for the script is not equal to 1
7. firstarg=$1
8. mkdir -p  -- if not create a directory , if exist ignore.
9. Remove last comma : sed 's/,$//'
10. Finding a private ip of a node where we have ssh access.
      ph=$(ssh $nodeip  '/sbin/ifconfig' >temp.txt)
      prip=$(cat temp.txt | grep -e "inet:" -e "addr:" | grep -v "inet6" | grep -v "127.0.0.1" | head -n 1 | awk '{print $2}' | cut -c6-)

11.To print particular line in the given file on console.
       sed -n 9406p abcd.lib

12.Find and remove all files with .gz extension from /tmp folder which are more than 4 days old.
     find /tmp/ -mtime +4 -name'*.gz' -exec rm {} \;

13. Recursively search for word with  numbering on file line.
      grep -irn "searchword"

14. remove last two letters iff they are ab
      t_param="$(echo ${s_name/%ab/})"
      or
      t_param="${s_name/%ab/}"

15. run bash in debug mode
      set -x
      export 'PS4=+${BASH_SOURCE}:${LINENO}:${FUNCNAME[0]}():'

     myscript.sh 2>debug.log

16. Remove filename and last / from a directory
        echo "/home/abc/trail/filename.txt" | sed 's|\\(.*\\)/.*|\\1|'

17. Remove last digit from a variable
         sed -i "s/$avar_name[0-9]/$avar_name/g" "file_name"