Bash Guide (Handy guide for Dev)

a. Reading input

$ read var_name  #asks to input variable value
$ echo $var_name
$ echo "Hello, $var_name"

b. Crontab

Schedule automatically running jobs/scripts for the system background.

$ crontab -e  #create new cronjob

c. Wget

Download basically anything and everything on web.

$ wget -m -p -E -k www.example.com

The optional arguments are

-m, --mirror            Turns on recursion and time-stamping, sets infinite 
                          recursion depth, and keeps FTP directory listings.
-p, --page-requisites   Get all images, etc. needed to display HTML page.
-E, --adjust-extension  Save HTML/CSS files with .html/.css extensions.
-k, --convert-links     Make links in downloaded HTML point to local files.

To download complete website html only,

$ wget -m www.ktustudy.in

c. Piping & Grep

Piping takes the raw output into the next command. Grep filters output text with matched pattern.

$ cat *.html | grep "Secret"  #prints all line containing 'Secret'

d. Piping as input for program

$ python -c "print 'kelox'" | python name.py 
What's your name? 
Welcome, kelox

$ echo solo | python name.py 
What's your name? 
Welcome, solo

e. Sed (Stream Editor)

Performs searching, find and replace, insertion or deletion.

$ sed -i 's/old-text/new-text/g' input.txt.
$ cat *.html | sed 's/yooo/yasss/g' .   #replaces yooo with yasss