Command Line 2 - Revision history

Laurel at 00:44, 27 February 2009

2009-02-27T00:44:07Z

Rwlove: /* A handful of commands */

2007-05-05T19:48:56Z

A handful of commands

Rwlove: /* The pipe */

2007-05-05T19:44:59Z

The pipe

Rwlove: /* The pipe */

2007-05-05T19:44:38Z

The pipe

Rwlove: /* Option Arguments */

2007-05-05T19:29:44Z

Option Arguments

Rwlove at 19:27, 5 May 2007

2007-05-05T19:27:11Z

Rwlove: /* Lexing a command line, Part 1 */

2007-05-05T19:15:40Z

Lexing a command line, Part 1

Rwlove at 19:42, 14 April 2007

2007-04-14T19:42:42Z

Stillflame at 04:22, 23 August 2006

2006-08-23T04:22:24Z

MichaelWestwind: /* How do you do this? */ formatting. is this really the place for that comment?

2006-08-21T14:54:57Z

How do you do this?: formatting. is this really the place for that comment?

← Older revision		Revision as of 00:44, 27 February 2009
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	=Introduction=		=Introduction=
	You've taken the [[Basic_Linux_Command_Line_for_Builders\|Command Line]] class. You've QC'd a couple of boxen, and then you built a few. In the meantime, you've forgotten everything you learned in Command Line, except (I hope), tab completion. It's time to learn how it all works, fits together, and how to make sense of it all. Then you can go on to all the other topics in [[From User to Root\|From $ to #]].		You've taken the [[Basic_Linux_Command_Line_for_Builders\|Command Line]] class. You've QC'd a couple of boxen, and then you built a few. In the meantime, you've forgotten everything you learned in Command Line, except (I hope), tab completion. It's time to learn how it all works, fits together, and how to make sense of it all. Then you can go on to all the other topics in [[From User to Root\|From $ to #]].

@@ Line 124: / Line 124: @@
 *ls shows the files in the current directory, or a directory you ask of it.
 *cd changes your working directory.
 *mv moves a file.
 *head is a command which reads the top of a file or its input
@@ Line 132: / Line 133: @@
 *cut is a command with many many uses
 *ifconfig shows you the network status
 *grep will show lines that have the characters it's given as an argument.
 =How do you do this?=

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 It's time to introduce you to a second separator. In English, we have the space to separate symbols and allow us to lex, and then punctuation, to help us parse grammar. Without the period, we wouldn't really know where one idea ended and another began. Bash has something similar: the |. The |, called the Pipe, tells us that we have passed one idea to another. Technically what |ing does is send the output of the first command to be the input of the second command. So imagine you wrote out a command that would give you a lot of output, say, cat /etc/inittab and what you really wanted to do was look at only the five four lines of it. There's a command to look at the first five lines: head -n 5. Now we can put them together:
-  cat /dev/urandom | head -n 5
+  cat /etc/inittab | head -n 5
 One idea blends into another.

@@ Line 111: / Line 111: @@
 =The pipe=
-It's time to introduce you to a second separator. In English, we have the space to separate symbols and allow us to lex, and then punctuation, to help us parse grammar. Without the period, we wouldn't really know where one idea ended and another began. Bash has something similar: the |. The |, called the Pipe, tells us that we have passed one idea to another. Technically what |ing does is send the output of the first command to be the input of the second command. So imagine you wrote out a command that would give you a lot of output, say, cat /dev/urandom and what you really wanted to do was look at only the first four lines of it. There's a command to look at the first four lines: head -n 4. Now we can put them together:
+It's time to introduce you to a second separator. In English, we have the space to separate symbols and allow us to lex, and then punctuation, to help us parse grammar. Without the period, we wouldn't really know where one idea ended and another began. Bash has something similar: the |. The |, called the Pipe, tells us that we have passed one idea to another. Technically what |ing does is send the output of the first command to be the input of the second command. So imagine you wrote out a command that would give you a lot of output, say, cat /etc/inittab and what you really wanted to do was look at only the five four lines of it. There's a command to look at the first five lines: head -n 5. Now we can put them together:
-  cat /dev/urandom | head -n 4
+  cat /dev/urandom | head -n 5
 One idea blends into another.
 =A handful of commands=

@@ Line 91: / Line 91: @@
 Usually options are just switches --- either you ignore it and it's off, or you add it in to turn it on.  Some options, however, take an argument all for themselves.
-   ls --sort=size -w 100
+   ls --sort=size
-Both of those options took an argument and kept it.  We can accomplish this by using an equals sign: "--sort=size", or it may be that you just have to know that the option in question is the kind that takes posession of the argument immediately after it.  "-w" is a good example for this. "-w" means how wide to format the output.
+The option took an argument and kept it.  We can accomplish this by using an equals sign: "--sort=size", or it may be that you just have to know that the option in question is the kind that takes posession of the argument immediately after it.  "--sort" is a good example for this. "--sort" means how to sort the output.
-   ls -w
+   ls --sort
-The above makes no sense to ls, because the -w option requires a number of columns to tell it how to format the output.  Correctly used, the command would look like this:
+The above makes no sense to ls, because the --sort option requires additional information to tell it how to sort the output.  Correctly used, the command would look like this:
-   ls -w 100
+   ls --sort=size
 ===Long and Short===

@@ Line 3: / Line 3: @@
 =Lexing a command line, Part 1=
-  guest@freekbox:~$ ls -la --sort=size -r -w 100 /etc/init.d/
+  guest@freekbox:~$ ls -la --sort=size -r /lib/modules/2.6.18-3-686/mod*
 Scared? It's simpler when you know how to lex. Lex, the verb, means to break a flow of information into meaningful symbols. It's a term specific to linguistics and computer science, so you may not know it, but you do it all the time. When reading this sentence you recognize spaces and turn the letters around the spaces into separate words. You could lex on commas, and,then,the,sentence,would,look,like,this. We lex in aural conversation as well, though the spaces aren't visible, they're something we have to be taught. This is why the last step of fluency in a foreign language is the most difficult: knowing when they're saying "heat it", as opposed to "He did."
@@ Line 13: / Line 13: @@
   --sort=size
   -r
-  -w
+  /lib/modules/2.6.18-3-686/mod*
 First off, lets just ignore the prompt.  "guest@freekbox:~$" is always going to be there, and does not get considered by any part of the executing programs - it's for you, the user, to know where you are (at the command line, silly).  After that, the most important of these is always the first one. Here's why.
@@ Line 33: / Line 31: @@
 Command line talks like Yoda. The first word is the command, the action. The binary, or the machine, in the above. So
-  guest@freekbox:~$ ls -la --sort=size -r -w 100 /home/lab* /home/class*
+  guest@freekbox:~$ ls -la --sort=size -r /lib/modules/2.6.18-3-686/mod*
-The only piece we care about immediately is ls. ls is a command to list files in a directory (we'll get there in a moment). To know anything else about the command line above we have to read man ls to find out how ls expects arguments. When we read ls, we find out that -l means one thing, -a means another, --sort=size means sort files by size, -r means reverse the order, -w gets passed the 100 and means format the output to 100 columns, and the last two pieces are the directories/files we want listed. The *s I'll explain in a bit, in Parsing Part 2.
+The only piece we care about immediately is ls. ls is a command to list files in a directory (we'll get there in a moment). To know anything else about the command line above we have to read man ls to find out how ls expects arguments. When we read ls, we find out that -l means one thing, -a means another, --sort=size means sort files by size, -r means reverse the order, and the last piece is the directories/files we want listed. The *s I'll explain in a bit, in Parsing Part 2.
 =Paths/Filesystem introduction=
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   /usr/lib/libdvd-read2
-  /lib/modules/2.6.10/kernel/driver/usb/pci/usb-hotplug/
+  /lib/modules/2.6.18-3-686/kernel/drivers/usb/
   file1

@@ Line 144: / Line 144: @@
 =How do you do this?=
-Your task: write a single line command (you can use |s) that prints out # if the fifth line of a particular file is commented out (i.e. has a # at the beginning of the line) or prints blank if it does not. Use the interfaces file in the network directory in etc as your file.
+Your task: write a single line command (you can use |s) that prints out # if the fifth line of a particular file is commented out (i.e. has a # at the beginning of the line) or does not print anything if it does not. Use the interfaces file in the network directory in etc as your file.
 N.B.: Although this can be done very easily with regular expressions, if you know them, I'd prefer you not use them, as the purpose of this exercise is to show your ability to put commands together, and, most importantly, to understand the grammatical structure of a lengthy command line.

@@ Line 150: / Line 150: @@
 My answer is below, in white.
-<font color="white">cat /etc/network/interfaces | head -n 5 | tail -n 1 | cut -c 1 | grep "#"
+ <font color="white">cat /etc/network/interfaces | head -n 5 | tail -n 1 | cut -c 1 | grep "#"
 usually works; it fails on files that have fewer than five lines with the last line beginning with a #.
 The head-tail chopping can be done correctly in all cases with either  head -n 5 | tail -n +5  or
- tail -n +5 | head -n 1 .   Note also that grep chokes on a raw #;  either "#" or \# is an ok pattern for #.</font>
+tail -n +5 | head -n 1 .   Note also that grep chokes on a raw #;  either "#" or \# is an ok pattern for #.</font>
 =Bash is a program=