Initial commit

- Cloned from https://gitlab.mynisum.com/devops/devops-foundation/tree/master/bash-scripting

bash-scripting.md

+# DevOps Foundation - Bash Scripting
+
+## Table of Contents
+
+[1-Script Parent path](#parentpath)
+
+[2-Quote Marks](#quotemarks)
+
+[3-Logic and comparisons](#logicalcomparison)
+
+[4-Conditional statements](#conditionalstmt)
+
+[5-Ranges](#ranges)
+
+[6-Iterations](#iterations)
+
+[7-Builtin Variables](#builtinvariables)
+
+[8-Math Operations](#mathoperations)
+
+[9-Defining and Initializing Array](#array)
+
+[10-Using awk](#awk)
+
+[11-Using sed](#sed)
+
+[12-Using tr](#tr)
+
+[13-Parameter Expansion](#parameterexpansion)
+
+
+
+<a name="parentpath"/>
+
+## Script Parent path
+
+---
+
+* Good practice to define Script folder if you reference
+* other scripts with respect to current script
+
+```
+PARENT_PATH=$( cd "$(dirname "${BASH_SOURCE[0]}")" ; pwd -P )
+```
+
+<a name="quotemarks"/>
+
+## Quote Marks
+
+---
+
+```
+echo 'fixed literal'
+foo=4
+echo "Interpolate variables such as $foo"
+echo "This is how we escape \"quotes\" within quotes"
+`excute another command` and assigns to a variable
+bar=`ls -l`
+bar=`date`
+```
+
+<a name="logicalcomparison"/>
+
+## Logic and comparisons
+
+---
+
+*Numeric Comparisons*
+
+| Comparison | Description |
+| --- | --- |
+| int1 -eq int2 | Returns True if int1 is equal to int2. |
+| int1 -ge int2 | Returns True if int1 is greater than or equal to int2. |
+| int1 -gt int2 | Returns True if int1 is greater than int2. |
+| int1 -le int2 | Returns True if int1 is less than or equal to int2 |
+| int1 -lt int2 | Returns True if int1 is less than int2 |
+| int1 -ne int2 | Returns True if int1 is not equal to int2 |
+
+
+*String Comparisons*
+
+| Comparison | Description |
+| --- | --- |
+| str1 == str2 	| Returns True if str1 is identical to str2. |
+| str1 != str2 | Returns True if str1 is not identical to str2. |
+| str | Returns True if str is not null. |
+| -n str | Returns True if the length of str is greater than zero. |
+| -z str | Returns True if the length of str is equal to zero. (zero is different than null) |
+
+*File Comparisons*
+
+| Comparison | Description |
+| --- | --- |
+| -d filename | Returns True if file, filename is a directory. |
+| -f filename | Returns True if file, filename is an ordinary file. |
+| -r filename | Returns True if file, filename can be read by the process. |
+| -s filename | Returns True if file, filename has a nonzero length. |
+| -w filename | Returns True if file, filename can be written by the process. |
+| -x filename | Returns True if file, filename is executable. |
+
+
+*Expression Comparisons*
+
+!expression
+
+Returns true if expression is not true
+expr1 -a expr2
+
+Returns True if expr1 and expr2 are true. ( && , and )
+expr1 -o expr2
+
+<a name="conditionalstmt"/>
+
+## Conditional Statement
+
+---
+
+If...then
+
+```
+if [ expression ]
+then
+	commands
+fi
+```
+
+If..then...else
+
+```
+if [ expression ]
+then
+	commands
+else
+	commands
+fi
+```
+
+If..then...else If...else
+
+```
+if [[ expression ]]
+then
+	commands
+elif [[ expression2 ]]
+then
+	commands
+else
+	commands
+fi
+```
+
+<a name="ranges"/>
+
+## Ranges
+
+---
+
+```
+echo {1..10}        	# prints 1 to 10
+echo {1..10..2}			# prints 1 to 10 incrementing by 2
+echo {a..z}        		# prints a to z
+echo {A..Z}         	# prints A to Z
+echo {A..Z}{1..2}  		# prints a combination A1 A2 B1 B2 C1 C2 ... 
+echo foo{A..Z}{1..2}	# prints a combination fooA1 fooA2 fooB1 fooB2 ... 
+
+echo $(seq 1 10)		# prints 1 to 10
+echo $(seq 1 2 10)		# prints 1 to 10 increment by 2
+```
+
+<a name="iterations"/>
+
+## Iteration (Loops)
+---
+
+```
+for var1 in list
+do
+	commands
+done
+```
+
+```
+while [ expression ]
+do
+	commands
+done
+```
+
+<a name="builtinvariables"/>
+
+## Built in variables
+
+---
+
+| Variable | Description |
+| --- | --- |
+| $1-$N | Stores the arguments (variables) that were passed to the shell program from the command line.|
+| $? | Stores the exit value of the last command that was executed.|
+| $0 | Stores the first word of the entered command (the name of the shell program). |
+| $* | Stores all the arguments that were entered on the command line ($1 $2 ...). |
+|"$@" | Stores all the arguments that were entered on the command line, individually quoted ("$1" "$2" ...). |
+
+<a name="mathoperations"/>
+
+## MATH Operations
+
+```
+op1=4
+op2=5
+result=$(( op1 + op2 ))		# result=9
+result=$(( op2 - op1 ))		# result=1
+
+result=$(( 4 * 5 ))			# result=20
+result=$(( 4 % 2 ))			# result=0
+result=$(( 4 % 2 == 0))		# result=1
+
+echo "$op1 * $op2" | bc  	# result=20
+echo "$op1 * 1.2" | bc 		# result=4.8
+```
+
+<a name="array"/>
+
+## Defining and Initializing Array
+
+```
+declare -a  array       # An empty array is defined
+
+array[0]=valA           # Setting value of a given array index
+array[1]=valB
+array[2]=valC
+
+array=( valA valB valC )  # another way
+
+${array[i]}               # displays array's value for this index.
+						  # If no index is supplied, array element 0 is assumed
+${#array[i]}              # to find out the length of any element in the array
+${#array[@]}              # to find out how many values there are in the array
+
+```
+
+<a name="awk"/>
+
+## Using AWK
+
+
+| Variable | Description |
+| --- | --- |
+| $0 | Complete line |
+| $1 | First column |
+| $2 | Second column |
+| $X | so on |
+| NF | Number of columns |
+| NR | Total lines |
+
+-F : Column Separator
+
+awk -F, ' { print $0 }'
+
+with search condition
+```
+awk -F, ' $1 == "foo" { print $0 }'	 myfile.csv  # Filter lines with 1st column "foo" and print
+
+awk -F, '{ print $3","$4" }' myfile.csv # Print column 3 and 4 of all lines
+```
+
+<a name="sed"/>
+
+## Using sed
+
+Syntax:
+sed 's/pattern/replacewith/g' inputfile
+
+where 'g' stands for Global. Multiple occurence of pattern will be replaced
+
+For Regex:
+^ Begin of Line
+$ End of Line
+
+Inplace substition of file
+-i : To change in file
+
+
+Example:
+The following statement will change the value enabled from 0 to 1 and display on screen. If '-i' is added in the arguments, it will change in the file
+
+```
+sed 's/enabled=0/enabled=1/'  /etc/yum.repos.d/CentOS-Vault.repo
+```
+
+<a name="tr"/>
+
+## Using tr
+
+Examples:
+
+```
+cat myfile | tr "is" "an"			# will change occurrance "i" with "a" and "s" with "n"
+cat myfile | tr ' ' ',' 		   # change space to comma
+cat myfile | tr ' ' '\n' 		   # change space to newline
+cat myfile | tr 'a-z' 'A-Z' 	   # Change lower case to upper case
+
+
+cat myfile | tr -d 'o' 		       # will delete occurance of "o"
+cat myfile | tr -s 				   # will remove double spaces to single space
+```
+
+<a name="parameterexpansion"/>
+
+## Parameter Expansion
+
+```
+${varname:-word}             # if varname exists and isn't null, return its value;
+							 # otherwise return word
+
+${varname:=word}             # if varname exists and isn't null, return its value;
+							 # otherwise set it word and then return its value
+
+
+FILE="/home/asad/test.tar.gz"
+echo "${FILE#*.}"     		 # print tar.gz
+echo "${FILE##*.}"    		 # print gz
+ext="${FILE#*.}"      		 # store output in a shell variable
+echo "$FILE has $ext"		 # display it
+```
+
+---
+
+## Questions:
+
+[1. Generate SQL](./questions/1-generate-sql.md)
+
+[2. Parse Columns](./questions/2-parse-columns.md)
+
+[3. String Manipulation](./questions/3-string-manipulation.md)
+
+[4. Iteration](./questions/4-iteration.md)
+
+[5. Generate Report](./questions/5-generate-report.md)

input/sample.txt

+1,Apple,Color is Red
+2,Mango,Color is Orange
+3,Banana,Color is Yellow
\ No newline at end of file

questions/1-generate-sql.md

+###1. Create a script to read a comma delimited file
+
+Read a CSV file containing 3 columns, as shown below and generating an output of SQL statements
+ 
+File: ./input/sample.txt
+
+```
+1,Apple,Color is Red
+2,Mango,Color is Orange
+3,Banana,Color is Yellow
+```
+ 
+
+Output file:
+
+```
+insert into myfruits (code,name,color) values (1,"Apple","Color is Red")
+insert into myfruits (code,name,color) values (2,"Mango","Color is Orange")
+insert into myfruits (code,name,color) values (3,"Banana","Color is Yellow")
+```

questions/2-parse-columns.md

+### 2. Parse column
+
+Given a username that exists locally on a linux machine, print home directory of the user. In case the user is not found. It should return an error
+
+hint: list of users and their home directory can be found in /etc/passwd
+
+#### Example 1
+
+```
+./myscript.sh root
+```
+
+Output:
+
+```
+Home directory: /var/root
+```
+
+#### Example 2
+
+```
+./myscript.sh usernonexists
+```
+
+Output:
+
+```
+User "usernonexists" not found
+```
+

questions/3-string-manipulation.md

+###3. String Manipulation
+
+Write a shell script that accept one or more file names as argument and prints all names in uppercase, provided they exist in current directory.
+
+Example: 
+```
+myscript.sh $(ls)
+```

questions/4-iteration.md

+### 4. Iteration
+
+Print Odd Number between 1 and 50
+
+Output:
+```
+Number is : 1
+Number is : 3
+Number is : 5
+Number is : 7
+Number is : 9
+.
+.
+```
\ No newline at end of file

questions/5-generate-report.md

+### 5. Generate Report
+Parse sample text file of timesheet users and generate customer will billable hours
+
+Input File: ./bin/timesheet.txt
+
+Output Sample:
+
+```
+Customer               : Hours     
+Creative minds         :     604.0
+Disney Arts            :    5494.0
+Enterprise solutions   :    1530.0
+Fake Enterprise        :     600.0
+Gadget Store           :    4332.0
+Kids Bank              :   10905.5
+King Kong carpenter    :     680.0
+Total                  :   26777.5
+```