modify files using sed in linux

 sed is a powerfull tool and you can find all details from here

delete a line containing a substring ("pattern")

sed -i '/pattern/d' file

replace a string

sed -e s/pattern//g -i file

using i.backup will keep a backup file of original and it is safer.  

sed -e "s/pattern//g" -i.backup file

Get parent directory name of shell script

 pwd | rev | cut -d/ -f1 | rev

lets see arguments for cut used with above command

spliting delimeter is given to -d, in this case \

required argument is given to -f, in this case 1

rev is used to reverse the string because parent directory name is the first argumet from reverse of pwd.

Get substring of a string in shell

 I wanted to get a only file names from the output of  command find . -maxdepth 1 -type d

This returns a strings contains "./" at the begining.

./1-case

./2-case

./3-case

./4-case

./5-case

./6-case

to remove first two characters i used command cut. as follows

echo "./1-case" | cut -c3-

-c means return characters

3- means from 3rd character to end

other examples

-c3 will return only 3rd character

-c3-4 will return characters form 3rd to 4th

 

Get the all folder names in current directory

 I wanted to copy a file from one location to multiple folders. We'll have to copy multiple times if we do it manally. Lets see how to use shell script to copy to every folder in one go using shell scripting.

main parts we need to do.

1. get all directories.

    find . -maxdepth 1 -type d

2. loop through every directory name, returned from 1, and copy file to each folder.

using foreach loop in s shell (.csh) 

> foreach dir ( ` find . -maxdepth 1 -type d` )
> foreach? cp ~/Scripts/convert.py $dir
> foreach? end

using for loop in bash shell (.sh)

Other commands to get all directory names

1. ls -d */
2. ls -l | grep `^d'

Overview of TDD and BDD

I wanted to know what are the differences between Test Driven Development and Behaviour Driven Development. So I went through many youtube videos and found following videos useful. 

Test Driven Development

Behaviour Diven Divelopment

Hello world of shell scripts

 

Just started recalling shell scripting again and I thought it would be good the post those somewhere.

So I started with following hello world. Not the simplest script, but it doesnt contain complex stuff. this script contains,

• How to comment,
• Output values using echo,
• Execute some simple commands,
• Assign output of a command to a variable,
• print variable values using echo.

Just ran above script to break the inertia and get me started.

lets see some basics about shell scripting.

Most people are confused with the extension of shell scripts at the begining. some scripts have .sh extension some have .csh extension. 

I found below stackoverflow answers are nicely explained about that.

SOF Link 1

SOF Link 2

Content from link 1

bash and sh are two different shells. Basically bash is sh, with more features and better syntax. Most commands work the same, but they are different.Bash (bash) is one of many available (yet the most commonly used) Unix shells. Bash stands for "Bourne Again SHell",and is a replacement/improvement of the original Bourne shell (sh).

Content from link 2

.sh is indicative of a script for the Bourne shell (sh) or the Bourne Again shell (bash), which is generally a superset of its predecessor.

.csh is indicative of a script for the C shell (csh), which, being a shell, is largely similar, but significantly different as soon as you start doing anything much more complex than running a series of static commands.

Both shells are generally available on any POSIXy environment, and indeed both are often preinstalled, though bash (and its cousin sh) are a little more ubiquitous in my experience.

I say 'indicative' above, because the idea of a file extension doesn't technically exist and has no semantic or syntactical meaning. A file could be named script.steve or documentation.exe or include.h and still actually be a shell script. For more definitive confirmation, look at the first line of the file. For a script designed to be executed directly, it should start with a shebang line, which starts with an octothorpe (#), a bang (!), and the path to the executable which should run the script. For example:

#!/usr/local/bin/bash

or

#!/usr/bin/python3