created shell dir

shell/AWK.txt

@@ -0,0 +1,37 @@
+AWK
+
+    * searches files for lines that contain certain pattern
+    * performs operation described in AWK body on line with certain
+      pattern.
+    * performs operation described in AWK body on choosen line
+
+
+    * Basic structure
+
+        awk 'program_you_will_write' input-file1 input-file2
+
+        awk 'BEGIN{
+            code_in_BEGIN_section
+        }
+
+        { code_in_main_body_section }
+
+        END{
+            code_in_END_section
+        }' input-file1 input-file2
+
+    * AWK Commands
+
+        * In AWK body bash features doesn't work
+        * Completely new language in AWK body
+            * print
+            * if-else
+            * for loop
+            * ...
+        
+        * Completely new features we can call on specific line (specific text)
+            * NF (number of fields)
+            * NR (number of records)
+            * RS (records separator)
+            * $1,$2,.. (specific fields)
+            * ...

shell/Bash-Scripting.txt

@@ -0,0 +1,662 @@
+-> ls :
+
+    List all the file or folder present in the current directory.
+
+        Option:
+
+        * -l :  List all the file and folder with permission, owner,
+                and group details in form of vertically alinged list.
+        
+        * -a :  Display hidden (.)dotfile as well.
+
+-> pwd :
+
+    Print the current directory, present on the terminal.
+
+-> date :
+
+    Print the current date and time.
+
+-> chmod :
+
+    Used to change the permission of file or folder
+
+        Symbol Meaning :
+
+        * a : For all (including owner, group and others)
+        * u : For owner
+        * g : For group
+        * o : For others
+        * r : read permission ( number 4 )
+        * w : write permission ( number 2 )
+        * x : execute permission ( number 1 )
+
+        Option :
+
+        * a+x : Add execute permission for all.
+        * a-x : Remove execute permission for all.
+        * 755 : rwx - user , r-x - group, r-x - others
+
+    How to use?
+
+        chmod a+x "file/folder name"
+        chmod 755 "file/folder name"
+
+-> echo :
+
+    To Print argument on the terminal
+
+        Option:
+
+        * -n : Not to add newline.
+        * ".." : String to print
+        * $PATH : variable ( environment variable, etc. )
+
+-> $PATH environment variable :
+
+    Store the paths which help in invoking executable, script, etc,
+    without specifying whole path, where its present.
+
+    How to add path to $PATH?
+
+    export PATH=$PATH:$(pwd)
+                        or full path to intended directory.
+
+-> SHABANG (#!/bin/bash)
+
+    Tells to use this interpreter to run the script.
+    Same as /bin/bash ./script
+
+-> Variables :
+
+    To stores data and can be changed.
+
+    1. Explicit Defination :
+        VAR=value
+        COUNT=5
+        PATH=/var/lib
+
+    2. Read command :
+        read VAR
+        read COUNT
+        read PATH
+
+        Option :
+
+        * -p :  to print the parameter before read.
+
+            How to use?
+
+                read -p "Your name: " NAME
+
+        * -s :  to hide the input to be taken. Best use
+                for password.
+
+            How to use?
+            
+                read -sp "Your age: " AGE
+
+    3. Command Substitution :
+
+        To store the output of the command executed to the variable.
+
+        How to use?
+
+            VAR=$(pwd) or VAR=`pwd`
+
+
+    How to use variables?
+
+        Use $variableName for using variables.
+
+
+-> For Math Calculation :
+
+    1 . let
+
+        let RESULT=NUMBER+5
+        let NUMBER++
+        let NUMBER--
+        let NUMBER+=5
+        let NUMBER-=5
+
+    2. (( ))
+
+        RESULT=$(( NUMBER + 5 ))
+    
+    3. []
+
+        RESULT=$[ NUMBER + 5 ]
+    
+    4. expr 
+
+        RESULT=$(expr $NUMBER + 5)
+        RESULT=`expr $NUMBER + 5`
+        RESULT=`expr 2 + 3`
+
+    5. bc ( used for floating point number )
+
+        RESULT=`echo "$NUMBER * 1.9" | bc`
+
+
+-> Argument :
+
+
+    $0 - script name
+    $1 - first argument
+    $2 - second argument
+    $n - nth argument
+    "$@" - all argument, expands as "$1" "$2" "$3"
+            and so on.
+    "$*" - all argument as string, "$1c$2c$3", 
+            where c is IFS (Internal field
+            separator), which is usally whitespace.
+    $# - arguments count
+
+-> Redirecting and piping:
+
+    Redirecting
+
+    * STDIN (0) - Standard input (data provided to program)
+    * STDOUT (1) - Standard output (what program prints, defaultly to the terminal)
+    * STDERR (2) - Standard error (what error message program prints, defaultly to terminal)
+
+    examples:
+    cat file1.txt > output_from_cat.txt
+    cat file1.txt 1>output_from_cat.txt
+    cat file1.txt 2>error.txt
+    cat file1.txt 1>output_from_cat.txt 2>error.txt
+    cat file1.txt &> output_from_cat.txt (from both 1 and 2)
+    cat file1.txt 1> output_from_cat.txt 2>&1(redirecting error to output)
+
+    cat file1.txt >> output_from_cat.txt(adding output instead of replacing it)
+
+    Piping
+
+    output of preceeding program is input to succeeding
+    program.
+
+    Program1 | Program2
+
+    examples:
+    cat file.txt | wc -l
+    cat file.txt | head -5 | tail -3 | wc -l
+
+-> Exit Status
+
+    echo $?
+
+    $? will give a return value of previous command.
+    It's the return value, called EXIT STATUS.
+    Successfully exiting give 0 value otherwise
+    non-zero value.
+
+    We can exit script using exit command.
+    exit command can be used with number 0 - 255.
+
+-> If Statement
+
+    if[ condition ]; then
+        ....
+    elif[ condition ]; then
+        ....
+    elif[ condition ]; then
+        ....
+    else
+        ....
+    fi
+
+    * AND with if statement ?
+
+    if[ condition ] && [ condition ]; then
+        ....
+    fi
+
+    * OR wiht if statement ?
+
+    if[ condition ] || [ condition ]; then
+        ....
+    fi
+
+    * Negate if condition
+
+    if[ !condition ]; then
+        ....
+    fi
+
+    if![ condition ]; then
+        ....
+    fi
+
+-> Mathematical comparison:
+
+    * Operands
+
+        $ -eq   equal to
+        $ -ne   not equal to
+        $ -gt   greater than
+        $ -lt   less than
+        $ -ge   greater than or equal to
+        $ -le   less than or equal to
+
+    Examples:
+
+        if [ $VAR -eq 5 ]; then
+        if [ $VAR -gt 7 ]; then
+        if [ $VAR -eq 5 ] && [ $COUNT -ne 1 ]; then
+
+
+
+-> String Comaparison
+
+    * Comapare two strings
+    [ "$STR1" = "$STR2" ]
+    [ "$STR1" != "$STR2" ]
+
+    [ "$STR1" = "hello" ]
+    [ "$STR1" != "hello" ]
+
+    * Compare two strings - quotation marks?
+      Bash can handle it in another way [[ ]]
+
+      [[ $STR1 = $STR2 ]]
+      [[ $STR1 != $STR2 ]]
+
+      [[ $STR1 = "hello" ]]
+      [[ $STR1  != "hello ]]
+
+      This is not widely used and most scripts
+      are using quotation marks with single 
+      brackets
+
+    * Test if string is empty
+
+        [ -z "$STR1" ] returns true if STR1 holds
+                        an empty string
+
+        [[ -z $STR1 ]] possible, but not widely used
+        
+        [ -n "$STR1" ] returns true if STR1 holds
+                        a non-empty string
+
+        [[ -n $STR1 ]] possible, but not widely used
+
+    * Alphabetically compare two strings
+
+    [[ $STR1 > $STR2 ]]
+
+    [[ $STR1 < $STR2 ]]
+
+    No choice!!!
+
+    * Wildcards
+
+        [[ $STR1 == string-with-wildcards ]]
+
+    * Regular expression
+
+        [[ $STR1 =~ $regex ]]
+
+
+-> Wildcards (globbing patterns)
+|-----------------------------------------------------------------------|
+|   Symbol  |   Description     |   Example     |   Example matches     |
+|-----------------------------------------------------------------------|
+|   ?       |   Single          |   hel?        |   help, hell,         |
+|           |   character       |               |   hel1....            |
+|-----------------------------------------------------------------------|
+|   *       |   Any number of   |   ca*         |   car,ca,carpet,      |
+|           |   characters      |               |   carpenter,car112..  |
+|           |   (including zero)|               |                       |
+|-----------------------------------------------------------------------|
+|   []      |   Single character|   file[0-2]   |   file0,file1,file2   |
+|           |   from range      |   [hd]ello    |   hello or dello      |
+|-----------------------------------------------------------------------|
+|   {}      |   Comma seperated |   {*.txt,     |   hello.txt,doc.txt,  |
+|           |   terms           |   *.pdf}      |   source.pdf, book.pdf|
+|-----------------------------------------------------------------------|
+|   [!]     |   Any character   |   file[!1]    |   file2,file3....     |
+|           |   listed in       |               |                       |
+|           |   brackets        |               |                       |
+|-----------------------------------------------------------------------|
+
+    * some useful character classes: (use it within [])
+
+    |-------------------------------------------|
+    |   [:upper:]   |   Uppercase character     |
+    |   [:lower:]   |   Lowercase character     |
+    |   [:alpha:]   |   Alphabetic character    |
+    |   [:digit:]   |   Number character        |
+    |   [:alnum:]   |   Alphanumric character   |
+    |               |   (alpha + digit)         |
+    |   [:space:]   |   whitespace character    |
+    |               |   (space, tab, newline)   |
+    |-------------------------------------------|
+
+* [[ $STRING == pattern_with_wildcards ]]
+* [[ $STRING == file[0-9].txt ]]
+* [[ $STRING == rich* ]]
+
+
+-> Regular Expressions
+
+|-----------------------------------------------------------|
+|   Symbol  |   Description |   Example |   Example matches |
+|-----------------------------------------------------------|
+|   .       |   any single  |   bo.k    |   book,bo1k, ...  |
+|           |   character   |           |                   |
+|-----------------------------------------------------------|
+|   *       |   preceeding  |   co*l    |   cl,col,cool, ...|
+|           |   item must   |           |                   |
+|           |   match zero  |           |                   |
+|           |   or more     |           |                   |
+|           |   times       |           |                   |
+|-----------------------------------------------------------|
+|   ^       |   Start of    |   ^hello  |   line starting   |
+|           |   the line    |           |   with hello      |
+|           |   marker      |           |                   |
+|-----------------------------------------------------------|
+|   $       |   End of the  |   hello$  |   line ending     |
+|           |   line marker |           |   with hello      |
+|-----------------------------------------------------------|
+|   []      |   Any one of  |   coo[kl] |   cook or cool    |
+|           |   of character|           |                   |
+|           |  enclosed in[]|           |                   |
+|-----------------------------------------------------------|
+|   [-]     |  Any character|  file[1-3]|  file1,file2,file3|
+|           |   within the  |           |                   |
+|           |   range       |           |                   |
+|-----------------------------------------------------------|
+|   [^]     |  Any character|   file[^0 |   file8,file9     |
+|           |   except those|   1234567]|                   |
+|           |   enclosed in |           |                   |
+|           |   brackets    |           |                   |
+|-----------------------------------------------------------|
+|   ?       |   preceeding  |   colou?r |   color,colour    |
+|           | item must     |           |   NOT colouur     |
+|           | one or zero   |           |                   |
+|           |   times       |           |                   |
+|-----------------------------------------------------------|
+|   +       | preceeding    |   file1+  |   file1,file11,   |
+|           | item must     |           |   file111         |
+|           | match one or  |           |   NOT file        |
+|           |   more times  |           |                   |
+|-----------------------------------------------------------|
+|   {n}     | preceeding    |   [0-9]{3}|   Any three digit:|
+|           | item must     |           |   097,256,787,... |
+|           | match n times |           |                   |
+|-----------------------------------------------------------|
+|   {n,}    | Minimum number|  [0-9]{3,}|   Any three digit |
+|           | of times the  |           |   111,097,256,787.|
+|           | preceeding    |           |                   |
+|           | item should   |           |                   |
+|           | match         |           |                   |
+|-----------------------------------------------------------|
+|   {n,m}   | Minimum and   | [0-9]{1,3}|   1,158,26, ...   |
+|           | maximum number|           |   NOT 1258,1111,..|
+|           | of times the  |           |                   |
+|           | preceeding    |           |                   |
+|           | item should   |           |                   |
+|           | match         |           |                   |
+|-----------------------------------------------------------|
+|   \       | Escape        |   hell\.o |   hell.o          |
+|           | character -   |           |   NOT:helllo,     |
+|           | escape any of |           |   hell1o...       |
+|           | the special   |           |                   |
+|           | character,    |           |                   |
+|           | ignore the    |           |                   |
+|           | meaning of    |           |                   |
+|           | them          |           |                   |
+|-----------------------------------------------------------|
+
+-> Regex in Bash
+
+    * [[ $STRING =~ $REGEX ]]
+    * REGEX="http://.*\.jpg"
+    * ${BASH_REMATCH[0]} -> part of the STRING which match
+                            REGEX (e.g. http://images.jpg)
+    * ${BASH_REMATCH[1]} -> part of the REGEX which is
+                            enclosed in first parentheses,
+                            e.g.
+                            REGEX="http://(.*)\.jpg" -> which
+                            would represents as "images"
+
+
+-> Filesystem Related Tests
+
+|-----------------------------------------------------------------------|
+|   File Test operators |   Description, what is returned               |
+|-----------------------------------------------------------------------|
+|   [ -e $VAR ]         |   True if variable hold existing file (file   |
+|                       |   or directory)                               |
+|-----------------------------------------------------------------------|
+|   [ -f $VAR ]         |   True if variable holds an existing regular  |
+|                       |   file                                        |
+|-----------------------------------------------------------------------|
+|   [ -d $VAR ]         |   True if variable holds an existing directory|
+|-----------------------------------------------------------------------|
+|   [ -x $VAR ]         |   True if variable is an executable file      |
+|-----------------------------------------------------------------------|
+|   [ -L $VAR ]         |   True if variable holds th path of a symlink |
+|-----------------------------------------------------------------------|
+|   [ -r $VAR ]         |   True if variable holds file that is readable|
+|-----------------------------------------------------------------------|
+|   [ -w $VAR ]         |   True if variable holds file that is writable|
+|-----------------------------------------------------------------------|
+
+        * Example:
+            if [ -f $FILE ]; then
+                echo File exists
+            else
+                echo File does not exists
+            fi
+
+-> && and ||
+
+    *examples
+        [ $? -eq 0 ] && echo command OK || echo something went wrong
+            |-----------------|                      |
+        if true             execute this             |
+                            if NOT true              |
+                                |--------------------|
+
+
+-> For loops
+
+    for arg in [list]
+    do
+        command(s)..
+    done
+
+    * Example 
+        for PLANET in "Mercury Venus Earth"
+        do
+            echo $PLANET
+        done
+
+        for file in *.txt
+        do
+            $file
+        done
+
+-> For loops - C style for loops
+
+    for ((i=1; i <= 10 ; i++))
+    do
+        echo $i
+    done
+
+-> While loop
+
+    while [ condition ]
+    do
+        command(s)
+    done
+
+-> C-style While loop
+
+    while (( condition ))
+    do
+        command(s)
+    done
+
+    * Example
+        A=1
+        LIMIT=10
+        while (( A < LIMIT )) //no $ here
+        do
+            touch $A
+            let A++
+        done
+
+-> Reading Files with While loop
+
+    while read line
+    do
+        command(s)..
+    done < "$FILENAME"
+
+    cat "$FILENAME" |
+    while read line
+    do
+        echo $line
+    done
+
+-> Case:
+
+    case "$VAR" in
+
+        "$condition1")
+            command(s)...
+        ;;
+        "$condition2")
+            command(s)...
+        ;;
+        *)
+        command(s)..
+        ;;
+    esac
+
+    *Example:
+
+    case "$(whoami)" in
+
+     "root")
+            echo you are root
+            ;;
+     "richard"|"susan")
+            echo you are user
+            ;;
+     *)
+            echo I don't know you
+            ;;
+    esac
+
+-> shift 
+    It's a command to throw away the parameter count
+    that is given to the script.
+
+
+-> getopts:
+
+    * easy way how to parse short positional parameters (-f)
+    * doesn't support long positional parameters ( --help )
+    
+    * getopts optstring name
+
+    -> For examples:
+
+        #!/bin/bash
+
+        while getopts a:b:cd param; do
+         case $param in                                                     OPTIND is initialized to 1
+            a)  echo ""                                                     each time the shell or a
+                echo "parameter 'a' with argument: $OPTARG"                 shell script is invoked.
+                ;;
+            b)  echo "parameter 'b' with argument: $OPTARG"                 getopts places index of the
+                ;;                                                          next argument to be
+            c)  echo "parameter 'c' selected (no colon, no argument)"       processed into the variable
+                ;;                                                          OPTIND
+            d)  echo "parameter 'd' selected (no colon, no argument)"
+                ;;
+         esac
+        done
+
+
+-> getopt:
+
+    * parse command options (enhanced)
+
+    opts=`getopt -o a::b:cde --long file::,name::,help -- "$@"`
+    eval set -- "$opts"
+
+    #!/bin/bash
+
+    echo "All arguments: $@"
+    opts=`getopt -o a::b:cde --long file::,name:,help -- "$@"`
+    eval set -- "$opts"
+    echo "All arguments after getopt: $@"
+
+-> Arrays:
+
+    * Declaration
+        * ARRAY=(value1 value2 .. valueN)
+        * ARRAY=(one,two,three)
+
+    * Calling
+        * ${ARRAY[0]}   #one
+        * ${ARRAY[1]}   #two
+        * ${ARRAY[2]}   #three
+
+    
+    * ARRAY=(one,two,three)
+
+        ${ARRAY[0]}     #one
+        ${ARRAY[1]}     #two
+        ${ARRAY[2]}     #three
+        ${ARRAY[@]}     #all items in Arrays
+        ${ARRAY[*]}     #all items in array, delimited by first character of IFS
+        ${!ARRAY[@]}    #all indexes in the array ( @/* )
+        ${#ARRAY[@]}    #number of items in the array ( @/* )
+        ${#ARRAY[0]}    #length of item zero
+
+-> Functions
+
+    * function_name(){
+        <commands>
+      }
+
+    * function function_name{
+        <commands>
+      }
+
+    * Example
+        | function hello{
+        |     echo hello
+        | }
+        |
+        | echo "output from function hello: "
+        | hello
+
+
+
+        | function hello{
+        |     echo hello $1
+        |     return 11
+        | }
+        |
+        | echo "output from function hello: "
+        | hello richard
+        | echo "return value from function hello is: $?"
+
+
+
+        | function hello {                      function hello{
+        |   name=$1                                 local name=$1
+        |   echo "hello $name"                      echo "hello $name"
+        | }                                     }
+        |
+        | echo "enter your name:"               echo "enter your name:"
+        | read name     #richard                read name       #richard
+        | hello Peter   #hello Peter            hello Peter     #hello Peter
+        | echo $name    #Peter                  echo $name      #richard

shell/arguments.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+IFS=","
+echo "Script name: $0"
+echo "First argument: $1"
+echo "Second argument: $2"
+echo "All arguments with \$@: $@"
+echo "All arguments with \$*: $*"
+echo "Arguments count: $#"

shell/array.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+
+ARRAY=($(ls *.txt))
+COUNT=0
+echo -e "FILE NAME \t WRITEABLE"
+for FILE in "${ARRAY[@]}"
+do
+    echo -n $FILE
+    echo -n "[${#ARRAY[$COUNT]}]"
+    if [ -w "$FILE" ]; then
+        echo -e "\t YES"
+    else
+        echo -e "\t NO"
+    fi
+
+    let COUNT++
+done

shell/case.sh

@@ -0,0 +1,43 @@
+#!/bin/bash
+
+#read data from users and make them option to recheck
+#if provided data are correct
+
+echo -n "Enter your name: "
+read NAME
+echo -n "Enter your age: "
+read AGE
+echo -n "Enter your department: "
+read DEP
+
+echo "You've entered following: "
+echo "Name:             $NAME"
+echo "AGE:              $AGE"
+echo "Department:       $DEP"
+
+CHECK=0
+while [ $CHECK -eq 0 ]
+do
+
+    echo -n "Is that correct? [Y/n] "
+    read ANSWER
+
+    case "$ANSWER" in
+        "Y"|"y" )
+                echo "Name:         $NAME" >> empl.txt
+                echo "AGE:          $AGE"  >> empl.txt
+                echo "Department:   $DEP"  >> empl.txt
+                echo "================================" >> empl.txt
+                echo "Your data were saved into employee file"
+                CHECK=1
+                ;;
+        "N"|"n" )
+                echo "Nothing was saved, run the script again \
+if you want to add data to employee file"
+                CHECK=1
+                ;;
+        * )
+                echo "Wrong answer provided"
+    esac
+
+done

shell/filetest.sh

@@ -0,0 +1,49 @@
+#!/bin/bash
+
+#for provided file print the summary of what permissions users has granted
+#example:   ./filetest.sh hello.txt
+#READ:      YES
+#WRITE:     NO
+#EXECUTABLE:NO
+
+#argument check
+
+if [ $# -ne 1 ]; then
+    echo "Provide exactly one argument"
+    exit 1
+fi
+
+#variable assignment
+FILE=$1
+
+#check if the file exists 
+if [ -f $FILE ]; then
+
+    #default variables
+    VAR_READ="NO"
+    VAR_WRITE="NO"
+    VAR_EXEC="NO"
+
+    #check if file is readable
+    if [ -r $FILE ]; then
+        VAR_READ="YES"
+    fi
+
+    #check if file is writable
+    if [ -w $FILE ]; then
+        VAR_WRITE="YES"
+    fi
+
+    #check if file is executable
+    if [ -x $FILE ]; then
+        VAR_EXEC="YES"
+    fi
+
+    #write permissions summary to user
+    echo "==FILE:   $FILE=="
+    echo "READ:         $VAR_READ"
+    echo "WRITE:        $VAR_WRITE"
+    echo "EXECUTABLE:   $VAR_EXEC"
+else
+    echo $FILE does not exists
+fi

shell/function.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+
+function addition {
+    local FIRST=$1
+    local SECOND=$2
+
+    let RESULT=FIRST+SECOND
+    echo "Result is: $RESULT"
+    let FIRST++
+    let SECOND++
+    return $RESULT
+}
+
+#do the addition of two numbers
+echo -n "Enter first number: "
+read FIRST
+echo -n "Enter second number: "
+read SECOND
+addition $FIRST $SECOND
+
+echo "RETURN: $?"
+echo "Printing variable:"
+echo "FIRST: $FIRST"
+echo "SECOND: $SECOND"

shell/getopt.sh

@@ -0,0 +1,40 @@
+#!/bin/bash
+
+echo "All arguments: $@"
+
+opts=`getopt -o a::b:cde --long file::,name:,help -- "$@"`
+eval set -- "$opts"
+echo "All arguments after getopt: $@"
+
+while [ $# -gt 0 ]
+do
+    case "$1" in
+        -a) echo "parameter 'a' selected with argument: $2"
+            shift 2 #same of 2 shift command
+            ;;
+        -b) echo "parameter 'b' selected with argument: $2"
+            shift 2
+            ;;
+        -c) echo "paramter 'c' selected"
+            shift
+            ;;
+        -d) echo "paramter 'd' selected"
+            shift
+            ;;
+        -e) echo "paramter 'e' selected"
+            shift
+            ;;
+        --file) echo "parameter 'file' selected with argument: $2"
+                shift 2
+                ;;
+        --name) echo "parameter 'name' selected with argument: $2"
+                shift 2
+                ;;
+        --help) echo "parameter 'help' selected"
+                shift
+                ;;
+        *)      echo "something else: $1"
+                shift
+                ;;
+    esac
+done

shell/getopts.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+while getopts a:b:cd param;
+do
+    case $param in
+        a) echo "parameter 'a' with argument: $OPTARG"
+            ;;
+        b) echo "parameter 'b' selected with argument: $OPTARG"
+            ;;
+        c) echo "parameter 'c' selected (no colon, no argument)"
+            ;;
+        d) echo "parameter 'd' selected"
+            ;;
+    esac
+done

shell/print.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+#create script for printing files, which will display
+#also line numbers
+
+#argument check
+if [ $# -ne 1 ]; then
+    echo "Exactly one arugment is needed, run: $0 file-path"
+    exit 1
+fi
+
+#check if provided argument is a file
+if ! [ -f "$1" ]; then
+    echo "File you've specified doesn't exist"
+    exit 2
+fi
+
+FILENAME=$1
+COUNT=1
+
+while read line
+do
+    echo "$COUNT: $line"
+    let COUNT++
+done < "$FILENAME"

shell/regex.sh

@@ -0,0 +1,38 @@
+#!/bin/bash
+
+#provide one word/sentence as an argument to the script.
+#If in that sentence will be ip addresss, find out, if that
+#ip address is reachable or not.
+
+#argument check
+if [ $# -ne 1 ]; then
+    echo "Provide exactly one argument e.g. $0 argument"
+    exit 1
+fi
+
+VAR1=$1
+#ip address regex
+REGEX="[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[[:digit:]]{1,3}"
+
+#regex check
+if ! [[ $VAR1 =~ $REGEX ]]; then
+    echo "No IP address provided"
+    exit 2
+fi
+
+IP=${BASH_REMATCH[0]}
+
+#find if ip address is reachable or not
+ping -c4 $IP 1>/dev/null
+
+#1>/dev/null
+#It will redirect standard output and prevent
+#any output to print on screen.
+
+if [ $? -eq 0 ]; then
+    STATUS="ALIVE"
+else
+    STATUS="DEAD"
+fi
+
+echo "IP found: $IP ($STATUS)"

shell/secret.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+echo -n Your age:
+read AGE
+
+#Problem with output as () cause to execute command in subshell.
+#[ $AGE -lt 20 ] && (echo You are not allowed to see secret; exit 1) || echo Welcome
+
+#command execute it same shell
+[ $AGE -lt 20 ] && { echo You are not allowed to see secret; exit 1;} || echo Welcome
+
+echo Secret is that there is no secret

shell/text.txt

@@ -0,0 +1,4 @@
+line 1
+line 2
+something 3
+something 4

shell/time_measurement.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+#start time measurement from here
+START=$(date +%s)
+CURRENT_DIRECTORY=$(pwd)
+sleep 2 #sleep 2 seconds
+END=$(date +%s)
+
+#end time measurement
+DIFFERENCE=$(( END - START ))
+
+echo
+echo Time elapsed: $DIFFERENCE seconds.