Difference between revisions of "BASH/C2/Conditional-execution/English-timed"

|'''Time'''

|'''Narration'''

| Use of '''test''' command and

| '''Conditional''' statements.  

| If not, for relevant tutorials, please visit our website which is as shown.

| '''Ubuntu Linux 12.04 ''' OS and

| '''GNU Bash''' version '''4.1.10'''

| It returns 0 (zero) for '''True''' and '''1''' (one) for '''False'''.

| '''Return''' value depends on the evaluation of the expression.

| One can get the '''return''' status by typing Dollar and question mark sign ($?).  

| One- by using the keyword ''' test'''.

| And other by using the expression enclosed within square brackets.

| It returns  zero  which means ''' True'''.  

| '''opening square bracket space 4 space hyphen eq space 4 space closing square bracket semicolon space echo space''' dollar sign and a question mark. Press '''Enter'''.

|  It returns zero which means ''' True'''.  

| Let's take another expression. Type:

'''test space 4 space hyphen eq space 5 semicolon space echo space''' dollar sign question mark.

| It returns one which means '''False'''.  

| opening square bracket space '''4''' space hyphen '''eq''' space '''5''' space closing square bracket semicolon space '''echo''' space dollar sign and a question mark. Press '''Enter'''.

| It also returns one which means '''False'''.  

| Now, let us go back to our '''slides'''.

| On the next line, type: '''commands''' or  '''statements''' that you want to '''execute'''.

| Lastly, end the '''if''' loop with '''fi.'''

| The basic rules of '''condition''' are:

| Always keep spaces between the brackets and the expression.

| Always terminate the line using semicolon before keyword “'''then”'''.

| Semicolon is used to terminate the statement or an expression.

|  It is recommended to quote '''string variables''' if you use them in '''condition'''.

| Let us see an example on '''if''' statement.

| Come back to our '''terminal'''.

| This is the first line of '''Bash shell script''' known as '''shebang line.'''

| An integer 100 is assigned to a variable '''count.'''

| Here, '''-eq''' is comparison operator.

| If the '''condition''' is True, it will display the message '''count is 100'''.

| Now '''save''' the file by pressing''' Ctrl + S'''.

| Try changing the value of variable '''count ''' and '''execute''' the script.

|  Now switch back to our '''slides'''.  

| On the next line, type commands.

| And again type some other commands.

| Come back to the '''terminal'''.

| I will open the file '''ifelse.sh'''.

| As '''abc123''' is a string, it should be written within double-quotes.

| The '''read''' command reads one line of data from the '''standard input.'''

| In this case, '''standard input''' is our keyboard.

| Hyphen '''s''' is for '''silent mode'''

| which means the entered password will not be displayed as we type.

| Hyphen '''p''' is for '''prompt'''.

| It will display a string “'Enter password: ” before it takes '''input''' from user.

| '''mypassword''' is a variable.

| If the password matches, it displays the message:

|  Now '''save''' the file by pressing '''Ctrl, s'''.

| Come back to our '''terminal''', make the file executable. Type:'''chmod''' space '''plus x''' space '''ifelse.sh'''. Press '''Enter.'''

| Type: '''dot slash ifelse.sh .''' Press ''' Enter.'''

| '''Enter password''': I will type '''abc'''. Press '''Enter'''.

| It is displayed as: '''Password accepted'''.

| In this tutorial, we have covered usage of '''test''' command, simple '''if''' statement and '''if-else '''statement.

| Write a script, take your name as an input.

| It should check this name with your system's username.

| Else, it should display “'''Try again'''”.

| Spoken Tutorial project is a part of the "Talk to a Teacher" project.