Difference between revisions of "Linux/C2/The-Linux-Environment/English-timed"

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{| border=1
 
{| border=1
−
!Time
+
|'''Time'''
−
!Narration
+
|'''Narration'''
 
|-
 
|-
  
 
|00:00
 
|00:00
−
|Welcome to this spoken tutorial on the Linux environment and ways to manupulate it.
+
|Welcome to this spoken tutorial on '''The Linux Environment''' and ways to manipulate it.
 
|-
 
|-
 
|00:07
 
|00:07
−
|A working linux system, preferably Ubuntu will be required to try out the examples illustrated in this tutorial.
+
|A working Linux system, preferably Ubuntu will be required to try out the examples illustrated in this tutorial.
 
|-
 
|-
 
|00:13
 
|00:13
−
|We assume that you know how to get started with the Linux operating system and have some basic idea about commands, file systems and shell .
+
|We assume that you know how to get started with the Linux operating system and have some basic idea about '''commands, file systems''' and '''shell'''.
 
|-
 
|-
 
|00:22
 
|00:22
−
|If you are interested, or need to brush these concepts up , please feel free to do so through another spoken tutorial available on our website.
+
|If you are interested or need to brush these concepts up, please feel free to do so through another spoken tutorial available on our website.
 
|-
 
|-
 
|00:32
 
|00:32
−
|Please note that Ubuntu 10.10 was used for recording this tutorial.
+
|Please note that '''Ubuntu 10.10''' was used for recording this tutorial.
 
|-
 
|-
 
|00:36
 
|00:36
−
|Please also note that Linux is case sensitive and all the commands used in this tutorial are in lower case unless otherwise mentioned.
+
|Please also note that Linux is ''case sensitive'' and all the commands used in this tutorial are in lower case unless otherwise mentioned.
 
|-
 
|-
 
|00:46
 
|00:46
Line 26: Line 26:
 
|-
 
|-
 
|00:55
 
|00:55
−
|Linux can be highly customized by changing the settings of the shell.  
+
|Linux can be highly customized by changing the settings of the '''shell'''.  
 +
 
 
|-
 
|-
 
|00:58
 
|00:58
−
|Let us understand how all this can be done.
+
|Let us understand how all this can be done.The behavior of the shell is generally determined by the '''shell variables'''.
−
|-
+
 
−
|00:59
+
−
|The behaviour of the shell is generally determined by the shell variables.
+
 
|-
 
|-
 
|01:04  
 
|01:04  
−
|There are mainly two kinds of shell variables:
+
|There are mainly two kinds of shell variables: '''Environment Variables''' and '''Local Variables'''.
−
 
+
−
Environment Variables and
+
−
 
+
−
Local Variables
+
 
|-
 
|-
 
|01:12
 
|01:12
Line 45: Line 40:
 
|-
 
|-
 
|01:19
 
|01:19
−
|These are also available in subshells spawned by the shell like the ones for running shell scripts.  
+
|These are also available in sub-shells spawned by the shell like the ones for running '''shell scripts'''.  
 
|-
 
|-
 
|01:24
 
|01:24
−
|Local Variables , which as the name suggests have a more restricted or limited availability.  
+
|Local Variables, which as the name suggests, have a more restricted or limited availability.  
 
|-
 
|-
 
|01:31
 
|01:31
−
|These are not available in the subshells spawned by the shell.  
+
|These are not available in the sub-shells spawned by the shell.  
 
|-
 
|-
 
|01:36  
 
|01:36  
−
|While in this tutorial, we will mainly talk about environment variables, let us first see how the value of these shell variables can be seen.
+
|While in this tutorial, we will mainly talk about environment variables. Let us first see how the value of these shell variables can be seen.
 
|-
 
|-
 
|01:48
 
|01:48
−
|To see all the variables available in the current shell , we run the command set.
+
|To see all the variables available in the current shell, we run the command '''set'''.
 
|-
 
|-
 
|01:53
 
|01:53
−
| '''Type at the terminal'''
+
| Type at the terminal: '''set''' space pipeline character '''more''' and press Enter.
−
"set space 'vertical-bar' more" and press enter.
+
 
|-
 
|-
 
|02:00
 
|02:00
−
|We can see all the current shell variables ,
+
|We can see all the current shell variables.
 
|-
 
|-
 
|02:04
 
|02:04
−
|For example : take a look at the HOME environment variable also notice the value assigned to it.
+
|For example: take a look at the '''HOME''' environment variable, also notice the value assigned to it.
 
|-
 
|-
 
|02:15
 
|02:15
−
|press Enter to move through the list and in order to come out press q
+
|Press '''Enter''' to move through the list and in order to come out press '''q'''.
 
|-
 
|-
 
|02:21
 
|02:21
−
|Here the output from set was pipelined to more in order to display a more systematic multipage output of the variable list.
+
|Here, the output from '''set''' was pipelined to '''more''' in order to display a more systematic multipage output of the variable list.
 
|-
 
|-
 
|02:38
 
|02:38
−
|To see only the environment variables run the command env
+
|To see only the environment variables, run the command '''env'''.
 
|-
 
|-
 
|02:45
 
|02:45
−
|'''Type at the terminal'''
+
|Type at the terminal:'''env''' space 'vertical-bar' '''more''' and press Enter.
−
 
+
−
"env  space 'vertical-bar' more" and press enter
+
 
|-
 
|-
 
|02:52
 
|02:52
−
|For example,
+
|For example, notice the '''SHELL''' variable whose value is '''slash bin slash bash'''.  
−
 
+
−
Notice the SHELL variable whose value is slash bin slash bash .  
+
 
|-
 
|-
 
|03:00
 
|03:00
−
|Again, you may press q to come out of the list.
+
|Again, you may press '''q''' to come out of the list.
 
|-
 
|-
 
|03:07
 
|03:07
−
|Now let us discuss some of the more important environment variables in linux.  
+
|Now let us discuss some of the more important environment variables in Linux.  
 
|-
 
|-
 
|03:11
 
|03:11
Line 101: Line 91:
 
|-
 
|-
 
|03:19
 
|03:19
−
|To see what a variable actually stores we have to prefix a dollar sign to the name of that variable and use the echo command along with it.
+
|To see what a variable actually stores, we have to prefix a dollar sign to the name of that variable and use the '''echo''' command along with it.
 
|-
 
|-
 
|03:30
 
|03:30
−
|The first environment variable that we would see is the SHELL variable.  
+
|The first environment variable that we would see is the '''SHELL''' variable.  
 
|-
 
|-
 
|03:35
 
|03:35
Line 110: Line 100:
 
|-
 
|-
 
|03:37
 
|03:37
−
|To see what is the value of the SHELL variable, type
+
|To see what is the value of the '''SHELL''' variable, type at the terminal: '''echo''' space '''dollar S-H-E-L-L''' in capital and press '''Enter.'''
−
 
+
−
at the terminal "echo space dollar S-H-E-L-L in capital"and press enter.
+
 
|-
 
|-
 
|03:55
 
|03:55
−
|Here slash bin slash bash is the shell where we are currently operating.
+
|Here, '''slash bin slash bash''' is the shell where we are currently operating.
 
|-
 
|-
 
|04:02
 
|04:02
−
|The next variable is the HOME.
+
|The next variable is '''HOME.'''
 
|-
 
|-
 
|04:05
 
|04:05
Line 124: Line 112:
 
|-
 
|-
 
|04:11
 
|04:11
−
|This directory is called the home directory and this is exactly what is available in HOME variable.
+
|This directory is called the 'home directory' and this is exactly what is available in 'HOME' variable.
 
|-
 
|-
 
|04:17  
 
|04:17  
−
|To see the value, type at the terminal "echo space dollar H-O-M-E in capital"and press enter
+
|To see the value, type at the terminal: '''echo''' space '''dollar H-O-M-E''' in capital and press '''Enter'''.
 
|-
 
|-
 
|04:29
 
|04:29
−
|The next environment variable is  PATH.
+
|The next environment variable is  '''PATH.'''
 
|-
 
|-
 
|04:32
 
|04:32
−
|The PATH variable contains the absolute paths of the directories that the shell is supposed to search for locating any executable command.
+
|The '''PATH''' variable contains the '''absolute paths''' of the directories that the shell is supposed to search for locating any executable command.
 
|-
 
|-
 
|04:40  
 
|04:40  
−
|Lets see the value of the path variable.
+
|Let's see the value of the path variable.
 
|-
 
|-
 
|04:43  
 
|04:43  
−
|Again, type at the terminal "echo space dollar P-A-T-H " in capitals and press enter
+
|Again, type at the terminal: '''echo''' space '''dollar P-A-T-H ''' in capitals and press Enter.
 
|-
 
|-
 
|04:51  
 
|04:51  
−
|On my computer it shows the directories
+
|On my computer it shows '''slash user slash local slash sbin slash user slash local slash bin slash user slash sbin slash user slash bin''' etc.
−
 
+
−
slash user slash local slash sbin slash user slash local slash bin slash user slash sbin slash user slash bin etc.
+
 
|-
 
|-
 
|05:04
 
|05:04
−
|This may slightly vary from one system to other.  
+
|This may slightly vary from one system to another.
 
|-
 
|-
 
|05:07
 
|05:07
Line 156: Line 142:
 
|-
 
|-
 
|05:25  
 
|05:25  
−
|In order to add our own directory type at the terminal  
+
|In order to add our own directory type at the terminal:
 
|-
 
|-
−
|5:29
+
|05:29
−
|"P-A-T-H in capital 'equal-to' dollar P-A-T-H again in capital colon  slash home slash the name of my own home directory and press enter.
+
|'''P-A-T-H''' in capital 'equal-to' '''dollar P-A-T-H''' again in capital '''colon  slash home slash''' the name of my own home directory and press Enter.
 
|-
 
|-
 
|05:54  
 
|05:54  
−
|Now if we echo the value of PATH,  
+
|Now if we '''echo''' the value of '''PATH''',  
 
|-
 
|-
 
|06:04  
 
|06:04  
−
|our added directory will also be a part of the PATH variable.  
+
|our added directory will also be a part of the '''PATH''' variable.  
 
|-
 
|-
 
|06:10
 
|06:10
Line 171: Line 157:
 
|-
 
|-
 
|06:16
 
|06:16
−
|Another interesting variable is the LOGNAME.
+
|Another interesting variable is the '''LOGNAME.'''
 
|-
 
|-
 
|06:20  
 
|06:20  
Line 177: Line 163:
 
|-
 
|-
 
|06:24  
 
|06:24  
−
|In order to see the value type "echo space dollar LOGNAME" and press enter.
+
|In order to see the value, type: '''echo''' space '''dollar LOGNAME''' and press '''Enter.'''
 
|-
 
|-
 
|06:35
 
|06:35
−
|When we open the terminal we can see the dollar sign, which is the prompt at which we enter all our commands.  
+
|When we open the terminal we can see the dollar sign which is the prompt at which we enter all our commands.  
 
|-
 
|-
 
|06:42
 
|06:42
−
|This is the primary prompt string represented by the environment variable PS1.  
+
|This is the primary prompt string represented by the environment variable 'PS1'.  
 
|-
 
|-
 
|06:47
 
|06:47
−
|There is a secondary prompt string also
+
|There is a secondary prompt string also.
 
|-
 
|-
 
|06:50
 
|06:50
−
|If our command is long and it spans for more than one line then from the second line onwards we can see a greater than sign “>” as the prompt
+
|If our command is long and it spans for more than one line then from the second line onwards we can see a greater than sign “>” as the prompt.
 
|-
 
|-
 
|07:00  
 
|07:00  
−
|This is the secondary prompt string represented by the environment variable PS2.
+
|This is the secondary prompt string represented by the environment variable 'PS2'.
 
|-
 
|-
 
|07:05  
 
|07:05  
−
|To see the value of the secondary command prompt, type at the terminal "echo space dollar PS2  and press enter.
+
|To see the value of the secondary command prompt, type at the terminal: '''echo''' space '''dollar PS2''' and press '''Enter.'''
 
|-
 
|-
 
|07:20
 
|07:20
Line 201: Line 187:
 
|-
 
|-
 
|07:28  
 
|07:28  
−
|In order to get this done
+
|In order to get this done, type ''' PS1''' 'equal-to' now within quotes 'at the rate' “@"and press Enter.
−
 
+
−
Type "PS1  'equal-to' now within quotes 'at the rate' “ and press enter.
+
 
|-
 
|-
 
|07:41
 
|07:41
−
|Now instead of the dollar sign we can see the at the rate sign as the prompt.
+
|Now instead of the '''dollar''' sign we can see the '''at the rate''' sign as the prompt.
 
|-
 
|-
 
|07:50
 
|07:50
Line 212: Line 196:
 
|-
 
|-
 
|07:56
 
|07:56
−
|Just type "PS1in capital 'equal-to' within quotes dollar LOGNAME " and press enter
+
|Just type: '''PS1''' in capital 'equal-to' within quotes '''dollar LOGNAME''' and press '''Enter'''.
 
|-
 
|-
 
|08:12  
 
|08:12  
Line 218: Line 202:
 
|-
 
|-
 
|08:16
 
|08:16
−
|To revert back type "PS1 'equal-to' dollar within quotes and press enter."
+
|To revert back, type: '''PS1''' 'equal-to' dollar within quotes and press Enter.
 
|-
 
|-
 
|08:28
 
|08:28
Line 230: Line 214:
 
|-
 
|-
 
|08:40
 
|08:40
−
|If we close the terminal and open it again or open a new terminal altogether and check the path variable by echoing its value
+
|If we close the terminal and open it again or open a new terminal altogether and check the path variable by echoing its value,
 
|-
 
|-
 
|09:00
 
|09:00
Line 241: Line 225:
 
|Often we want to re-execute a command that we had executed in the recent past. What do we do? Do we have to type the entire command again?
 
|Often we want to re-execute a command that we had executed in the recent past. What do we do? Do we have to type the entire command again?
 
|-
 
|-
−
|9:22
+
|09:22
 
| No, there are a number of solutions.
 
| No, there are a number of solutions.
 
|-
 
|-
 
|09:26
 
|09:26
−
|First, normally if you press the up  key on your keyboard then it will show the last command that you typed.  
+
|First, normally if you press the 'up  key' on your keyboard then it will show the last command that you typed.  
 
|-
 
|-
 
|09:33
 
|09:33
Line 254: Line 238:
 
|-
 
|-
 
|09:42
 
|09:42
−
|But when you have to scroll through many commands this becomes a little clumsy and tedious. A better way is to use the history command.
+
|But when you have to scroll through many commands this becomes a little clumsy and tedious. A better way is to use the '''history''' command.
 
|-
 
|-
 
|09:52  
 
|09:52  
−
|Type at the prompt "history"
+
|Type at the prompt '''history'''.
 
|-
 
|-
 
|09:58  
 
|09:58  
−
|and press enter, see a list of previously executed commands appears
+
|and press Enter, see a list of previously executed commands appear.
 
|-
 
|-
 
|10:04  
 
|10:04  
−
|If instead of the large list you want to see, only the last ten  
+
|If instead of the large list you want to see only the last ten,
 
|-
 
|-
 
|10:08  
 
|10:08  
−
|Type "history space 10" and press enter
+
|type '''history space 10''' and press ''Enter'''.
 
|-
 
|-
 
|10:20  
 
|10:20  
−
|Notice, in this list, there is a number assigned to each of the previously executed commands.  
+
|Notice, in this list there is a number assigned to each of the previously executed commands.  
 
|-
 
|-
 
|10:27
 
|10:27
−
|In order to repeat a particular command.
+
|In order to repeat a particular command,
 
|-
 
|-
 
|10:32
 
|10:32
−
|Just type exclamation mark followed by the number of the command for example 442 in my case would execute echo space dollar path
+
|just type exclamation mark followed by the number of the command for example 442 in my case would execute '''echo space dollar PATH'''
 
|-
 
|-
 
|10:51  
 
|10:51  
−
|If you need to re execute the last command simply type exclamation mark twice and press enter.
+
|If you need to re-execute the last command simply type exclamation mark twice and press Enter.
 
|-
 
|-
 
|11:03
 
|11:03
−
|The next thing we would see is called tilde substitution
+
|The next thing we would see is called 'tilde' substitution. The tilde(~) character is a shorthand for the home directory.
−
 
+
−
The tilde(~) character is a shorthand for the home directory.
+
 
|-
 
|-
 
|11:12
 
|11:12
−
|So say you have a directory with name testtree in your home directory. You can move to it by typing "cd space 'tilde' slash testtree".  
+
|So, say you have a directory with name testtree in your home directory. You can move to it by typing: '''cd''' space '''~(tilde)''' slash '''testtree'''.  
 
|-
 
|-
 
|11:25  
 
|11:25  
−
|One may also toggle between the current working directory and the last directory used by giving the command
+
|One may also toggle between the current working directory and the last directory used by giving the command '''cd  '~(tilde)' minus''' or only '''cd  minus'''
−
cd  'tilde' minus or only cd  minus  
+
 
|-
 
|-
 
|11:35
 
|11:35
−
|Like now that we are in the testtree directory, the last directory we visited was the home directory.   
+
|Like now that we are in the '''testtree''' directory, the last directory we visited was the home directory.   
 
|-
 
|-
 
|11:41
 
|11:41
−
|So if we run "cd space minus" and press enter. It will go to the home directory.  
+
|So if we run '''cd space minus''' and press Enter, it will go to the home directory.  
 
|-
 
|-
 
|11:47  
 
|11:47  
−
|Run it again and it will take us back to the testtree directory.
+
|Run it again and it will take us back to the '''testtree''' directory.
 
|-
 
|-
 
|11:55  
 
|11:55  
−
|The last but quite important command we will see is the alias command.  
+
|The last but quite important command we will see is the '''alias''' command.  
 
|-
 
|-
 
|11:59
 
|11:59
Line 308: Line 289:
 
|-
 
|-
 
|12:04
 
|12:04
−
|In this case we can give it a short alias name and use the alias name instead ,to invoke it.
+
|In this case we can give it a short '''alias''' name and use the '''alias''' name instead, to invoke it.
 
|-
 
|-
 
|12:11
 
|12:11
−
|Assuming that you have such a long directory hierarchy that you frequently visit for music, you may create an alias for it like this
+
|Assuming that you have such a long directory hierarchy that you frequently visit for music, you may create an alias for it like this.
 
|-
 
|-
 
|12:20
 
|12:20
−
|Type " alias space cdMusic 'equal-to' within double quotes cd space slash home slash arc slash files slash entertainment slash music " and press enter
+
|Type: '''alias''' space '''cdMusic''' 'equal-to' within double quotes '''cd space slash home slash arc slash files slash entertainment slash music''' and press Enter.
 
|-
 
|-
 
|12:47  
 
|12:47  
−
|Now every time you need to switch to this directory simply write cdMusic and press enter.  
+
|Now every time you need to switch to this directory simply write '''cdMusic''' and press Enter.  
 
|-
 
|-
 
|12:55
 
|12:55
−
|See, we are in the music directory now.
+
|See, we are in the '''music''' directory now.
 
|-
 
|-
 
|12:58
 
|12:58
−
|Now, you may type "cd space minus" at the prompt to go back to the previous working directory.  
+
|Now, you may type '''cd space minus ''' at the prompt to go back to the previous working directory.  
 
|-
 
|-
 
|13:08  
 
|13:08  
−
|To unset an alias simply write unalias space cdMusic and press enter
+
|To unset an '''alias''', simply write '''unalias space cdMusic''' and press Enter.
 
|-
 
|-
 
|13:20
 
|13:20
−
|Now again if you fire cdMusic from the terminal, you will get an error stating that the command was not found.
+
|Now again if you fire '''cdMusic''' from the terminal, you will get an error stating that the command was not found.
 
|-
 
|-
 
|13:30  
 
|13:30  
−
|Suppose we have two files, test1 and test2 in our present working directory
+
|Suppose we have two files, '''test1''' and '''test2''' in our present working directory
 
|-
 
|-
 
|13:38
 
|13:38
−
|and if we fire rm test1, test1 is silently deleted.
+
|and if we fire '''rm test1''', '''test1''' is silently deleted.
 
|-
 
|-
 
|13:45
 
|13:45
−
|We know that “hyphen i” option of the rm command  makes the removal process interactive.
+
|We know that '''hyphen i''' option of the '''rm''' command  makes the removal process interactive.
 
|-
 
|-
 
|13:52  
 
|13:52  
−
|So we may set an alias like, alias rm equal-to, now within quotes “rm space hyphen i”
+
|So we may set an '''alias''' like, '''alias rm''' equal-to, now within quotes '''rm space hyphen i'''
 
|-
 
|-
 
|14:03
 
|14:03
−
|Now when we run “rm” ,” rm hyphen i” will actually be run.
+
|Now when we run '''rm''' ,'''rm hyphen i'''will actually be run.
 
|-
 
|-
 
|14:13  
 
|14:13  
−
|So we saw that while test1 was silently deleted, system asked before deleting test2.
+
|So we saw that while '''test1''' was silently deleted, system asked before deleting '''test2.'''
 
|-
 
|-
 
|14:20  
 
|14:20  
−
|So, in this tutorial, you have learned about environment variables, history and aliasing.
+
|So, in this tutorial, you have learned about '''environment variables''', '''history''' and '''aliasing'''.
 
|-
 
|-
 
|14:25
 
|14:25
Line 362: Line 343:
 
|-
 
|-
 
|14:39  
 
|14:39  
−
|The Script for this tutorial was created by Anirban
+
|The Script for this tutorial was created by Anirban.
 
|-
 
|-
 
|14:42  
 
|14:42  
 
|This script has been contributed by ----------------------(name of the translator) and this is -----------------------(name of the recorder) from --------------------------(name of the place)signing off.
 
|This script has been contributed by ----------------------(name of the translator) and this is -----------------------(name of the recorder) from --------------------------(name of the place)signing off.
 
|}
 
|}

Latest revision as of 17:31, 23 March 2017

Time Narration
00:00 Welcome to this spoken tutorial on The Linux Environment and ways to manipulate it.
00:07 A working Linux system, preferably Ubuntu will be required to try out the examples illustrated in this tutorial.
00:13 We assume that you know how to get started with the Linux operating system and have some basic idea about commands, file systems and shell.
00:22 If you are interested or need to brush these concepts up, please feel free to do so through another spoken tutorial available on our website.
00:32 Please note that Ubuntu 10.10 was used for recording this tutorial.
00:36 Please also note that Linux is case sensitive and all the commands used in this tutorial are in lower case unless otherwise mentioned.
00:46 The Linux environment determines how the operating system behaves with you, how it responds to your commands, how it interprets your actions and so on.
00:55 Linux can be highly customized by changing the settings of the shell.
00:58 Let us understand how all this can be done.The behavior of the shell is generally determined by the shell variables.
01:04 There are mainly two kinds of shell variables: Environment Variables and Local Variables.
01:12 Environment variables, named so because they are available entirely in the user's total environment.
01:19 These are also available in sub-shells spawned by the shell like the ones for running shell scripts.
01:24 Local Variables, which as the name suggests, have a more restricted or limited availability.
01:31 These are not available in the sub-shells spawned by the shell.
01:36 While in this tutorial, we will mainly talk about environment variables. Let us first see how the value of these shell variables can be seen.
01:48 To see all the variables available in the current shell, we run the command set.
01:53 Type at the terminal: set space pipeline character more and press Enter.
02:00 We can see all the current shell variables.
02:04 For example: take a look at the HOME environment variable, also notice the value assigned to it.
02:15 Press Enter to move through the list and in order to come out press q.
02:21 Here, the output from set was pipelined to more in order to display a more systematic multipage output of the variable list.
02:38 To see only the environment variables, run the command env.
02:45 Type at the terminal:env space 'vertical-bar' more and press Enter.
02:52 For example, notice the SHELL variable whose value is slash bin slash bash.
03:00 Again, you may press q to come out of the list.
03:07 Now let us discuss some of the more important environment variables in Linux.
03:11 We would be using the bash shell for all our demonstrations here.
03:15 Different shells are customized in slightly different ways.
03:19 To see what a variable actually stores, we have to prefix a dollar sign to the name of that variable and use the echo command along with it.
03:30 The first environment variable that we would see is the SHELL variable.
03:35 It stores the name of the current shell.
03:37 To see what is the value of the SHELL variable, type at the terminal: echo space dollar S-H-E-L-L in capital and press Enter.
03:55 Here, slash bin slash bash is the shell where we are currently operating.
04:02 The next variable is HOME.
04:05 When we login into Linux, it normally places us in a directory named after our user name.
04:11 This directory is called the 'home directory' and this is exactly what is available in 'HOME' variable.
04:17 To see the value, type at the terminal: echo space dollar H-O-M-E in capital and press Enter.
04:29 The next environment variable is PATH.
04:32 The PATH variable contains the absolute paths of the directories that the shell is supposed to search for locating any executable command.
04:40 Let's see the value of the path variable.
04:43 Again, type at the terminal: echo space dollar P-A-T-H in capitals and press Enter.
04:51 On my computer it shows slash user slash local slash sbin slash user slash local slash bin slash user slash sbin slash user slash bin etc.
05:04 This may slightly vary from one system to another.
05:07 It is actually a list of directories separated by the :(colon) delimiter, that the shell would search in this order for finding an executable command.
05:18 We can also add our own directory to this list so that our directory is also searched by the shell.
05:25 In order to add our own directory type at the terminal:
05:29 P-A-T-H in capital 'equal-to' dollar P-A-T-H again in capital colon slash home slash the name of my own home directory and press Enter.
05:54 Now if we echo the value of PATH,
06:04 our added directory will also be a part of the PATH variable.
06:10 See the directory is now present here.
06:16 Another interesting variable is the LOGNAME.
06:20 It stores the username of the currently active user.
06:24 In order to see the value, type: echo space dollar LOGNAME and press Enter.
06:35 When we open the terminal we can see the dollar sign which is the prompt at which we enter all our commands.
06:42 This is the primary prompt string represented by the environment variable 'PS1'.
06:47 There is a secondary prompt string also.
06:50 If our command is long and it spans for more than one line then from the second line onwards we can see a greater than sign “>” as the prompt.
07:00 This is the secondary prompt string represented by the environment variable 'PS2'.
07:05 To see the value of the secondary command prompt, type at the terminal: echo space dollar PS2 and press Enter.
07:20 We may change our primary prompt string to say “at the rate” <@> at the prompt.
07:28 In order to get this done, type PS1 'equal-to' now within quotes 'at the rate' “@"and press Enter.
07:41 Now instead of the dollar sign we can see the at the rate sign as the prompt.
07:50 We may do something more interesting. Like we may display our username at the prompt.
07:56 Just type: PS1 in capital 'equal-to' within quotes dollar LOGNAME and press Enter.
08:12 Now my username is my prompt.
08:16 To revert back, type: PS1 'equal-to' dollar within quotes and press Enter.
08:28 We have assigned values to many of the environment variables.
08:32 But, remember one thing that these modifications are only applicable for the current session.
08:37 Like we had just added our directory to the PATH variable.
08:40 If we close the terminal and open it again or open a new terminal altogether and check the path variable by echoing its value,
09:00 we will be surprised to see that our modifications are no longer present.
09:05 The way by which we can make these modifications permanent will be covered in some advanced tutorial.
09:13 Often we want to re-execute a command that we had executed in the recent past. What do we do? Do we have to type the entire command again?
09:22 No, there are a number of solutions.
09:26 First, normally if you press the 'up key' on your keyboard then it will show the last command that you typed.
09:33 Keep pressing and it will keep scrolling through the previous commands.
09:37 To go back press the down key.
09:42 But when you have to scroll through many commands this becomes a little clumsy and tedious. A better way is to use the history command.
09:52 Type at the prompt history.
09:58 and press Enter, see a list of previously executed commands appear.
10:04 If instead of the large list you want to see only the last ten,
10:08 type history space 10' and press Enter.
10:20 Notice, in this list there is a number assigned to each of the previously executed commands.
10:27 In order to repeat a particular command,
10:32 just type exclamation mark followed by the number of the command for example 442 in my case would execute echo space dollar PATH
10:51 If you need to re-execute the last command simply type exclamation mark twice and press Enter.
11:03 The next thing we would see is called 'tilde' substitution. The tilde(~) character is a shorthand for the home directory.
11:12 So, say you have a directory with name testtree in your home directory. You can move to it by typing: cd space ~(tilde) slash testtree.
11:25 One may also toggle between the current working directory and the last directory used by giving the command cd '~(tilde)' minus or only cd minus
11:35 Like now that we are in the testtree directory, the last directory we visited was the home directory.
11:41 So if we run cd space minus and press Enter, it will go to the home directory.
11:47 Run it again and it will take us back to the testtree directory.
11:55 The last but quite important command we will see is the alias command.
11:59 It may happen that you have a large command that needs to be run again and again.
12:04 In this case we can give it a short alias name and use the alias name instead, to invoke it.
12:11 Assuming that you have such a long directory hierarchy that you frequently visit for music, you may create an alias for it like this.
12:20 Type: alias space cdMusic 'equal-to' within double quotes cd space slash home slash arc slash files slash entertainment slash music and press Enter.
12:47 Now every time you need to switch to this directory simply write cdMusic and press Enter.
12:55 See, we are in the music directory now.
12:58 Now, you may type cd space minus at the prompt to go back to the previous working directory.
13:08 To unset an alias, simply write unalias space cdMusic and press Enter.
13:20 Now again if you fire cdMusic from the terminal, you will get an error stating that the command was not found.
13:30 Suppose we have two files, test1 and test2 in our present working directory
13:38 and if we fire rm test1, test1 is silently deleted.
13:45 We know that hyphen i option of the rm command makes the removal process interactive.
13:52 So we may set an alias like, alias rm equal-to, now within quotes rm space hyphen i
14:03 Now when we run rm ,rm hyphen iwill actually be run.
14:13 So we saw that while test1 was silently deleted, system asked before deleting test2.
14:20 So, in this tutorial, you have learned about environment variables, history and aliasing.
14:25 This brings me to the end of this tutorial.
14:28 Spoken Tutorials are a part of the Talk to a Teacher project, supported by the National Mission on Education through ICT.
14:36 More information on the same is available from our website.
14:39 The Script for this tutorial was created by Anirban.
14:42 This script has been contributed by ----------------------(name of the translator) and this is -----------------------(name of the recorder) from --------------------------(name of the place)signing off.

Contributors and Content Editors

Minal, PoojaMoolya, Pratik kamble, Sandhya.np14

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