From 81d8fb60abcfce3adb10ceca38773e3ad3fe0d70 Mon Sep 17 00:00:00 2001 From: Milad Fatenejad Date: Sun, 1 Apr 2012 13:54:32 -0500 Subject: [PATCH] More updates --- 1-Shell/Readme.md | 121 +++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 110 insertions(+), 11 deletions(-) diff --git a/1-Shell/Readme.md b/1-Shell/Readme.md index 2408ac1..e1340bb 100644 --- a/1-Shell/Readme.md +++ b/1-Shell/Readme.md @@ -189,27 +189,126 @@ directory. ## Arguments Most programs take additional arguments that control their exact -behavior. For example, `-F` is an argument to `ls`. The `ls` program, -like many programs, take a lot of arguments. But how do we know what -the options are to particular commands? +behavior. For example, `-F` and `-l` are arguments to `ls`. The `ls` +program, like many programs, take a lot of arguments. But how do we +know what the options are to particular commands? Most commonly used shell programs have a manual. You can access the manual using the `man` program. Try entering: man ls -This will open the manual page for `ls`. Use the arrow keys to go up -and down. When you are done reading, just hit `q` to exit. +This will open the manual page for `ls`. Use the space key to go +forward and b to go backwards. When you are done reading, just hit `q` +to exit. Programs that are run from the shell can get extremely complicated. To -see an example, open up the manual page for the `gcc` program, which -is an open source C compiler and see just how complicated programs can -get! No one can possibly learn all of these arguments, of course. So -you will probably find yourself referring back to the manual page -frequently. +see an example, open up the manual page for the `mplayer` program, +which is command line driven video player. There are about 300 +arguments to the mplayer command. No one can possibly learn all of +these arguments, of course. So you will probably find yourself +referring back to the manual page frequently. + +**Examining the contents of other directories** + +By default, the `ls` commands lists the contents of the working +directory (i.e. the directory you are in). You can always find the +directory you are in using the `pwd` command. However, you can also +give `ls` the names of other directories to view. Navigate to the +home directory if you are not already there. Then enter the +command: + + ls UofCSCBC2012 + +This will list the contents of the `UofCSCBC2012` directory without +you having to navigate there. Now enter: + + ls UofCSCBC2012/1-Shell + +This prints the contents of `1-Shell`. The `cd` command works in a +similar way. Try entering: + + cd UofCSCBC2012/1-Shell + +and you will jump directly to `1-Shell` without having to go through +the intermediate directory. + +## Full vs. Relative Paths + +The `cd` command takes an argument which is the directory +name. Directories can be specified using either a *relative* path a +full *path*. The directories on the computer are arranged into a +hierarchy. The full path tells you where a directory is in that +hierarchy. Navigate to the home directory. Now, enter the `pwd` +command and you should see: + + /home/thw + +which is the full name of your home directory. This tells you that you +are in a directory called `thw`, which sits inside a directory called +`home` which sits inside the very top directory in the hierarchy. The +very top of the hierarchy is a directory called `/` which is usually +referred to as the *root directory*. So, to summarize: `thw` is a +directory in `home` which is a directory in `/`. + +Now enter the following command: + + cd /home/thw/UofCSCBC2012/1-Shell + +This jumps to `1-Shell`. Now go back to the home directory. We saw +earlier that the command: + + cd UofCSCBC2012/1-Shell + +had the same effect - it took us to the `1-Shell` directory. But, +instead of specifying the full path +(`/home/thw/UofCSCBC2012/1-Shell`), we specified a *relative path*. In +other words, we specified the path relative to our current +directory. A full path always starts with a `/`. A relative path does +not. You can usually use either a full path or a relative path +depending on what is most convenient. If we are in the home directory, +it is more convenient to just enter the relative path since it +involves less typing. + +Now, list the contents of the /bin directory. Do you see anything +familiar in there? + + +## Saving time with shortcuts and wild cards + +**Shortcuts** +There are some shortcuts which you should know about. Dealing with the +home directory is very common. So, in the shell the tilde character, +`~`, is a shortcut for your home directory. Navigate to the `1-Shell` +directory, then enter the command: + + ls ~ + +This prints the contents of your home directory, without you having to +type the full path. The shortcut `..` always refers to the directory +above your current directory. Thus: + + ls .. + +prints the contents of the `/home/thw/UofCSCBC2012`. You can chain +these together, so: + + ls ../../ + +prints the contents of `/home/thw` which is your home +directory. Finally, the special directory `.` always refers to your +current directory. So, `ls`, `ls .`, and `ls ././././.` all do the +same thing, they print the contents of the current directory. This may +seem like a useless shortcut right now, but we'll see when it is +needed in a little while. + +To summarize, the commands `ls ~`, `ls ~/.`, `ls ../../`, and `ls +/home/thw` all do exactly the same thing. These shortcuts are not +necessary, they are provided for your convenience. + -## Examining Files ## +## Examining Files The easiest way to examine a file ... -- 2.26.2