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The road to hell is paved with good intentions
Unix cd looks like an extremely primitive, elementary command, but it is not. Because as a mean of navigation of Unix filesystem it is hopelessly outdated, and environment in which it operated is extremely complex. Both sysadmin and regular users working on command like probably type this command more then any other. most of this typing is iether unnecessary or redundant. there are better ways to navigate Unix filesystem. See Norton Change Directory (NCD) clones and Orthodox File Managers for some ideas.
Another valuable idea is the idea of Directory favorites and in the most primitive form it can implemented with Pushd, popd and dirs
An that only a start ;-). You can also try to use for simplification of navigation cdpath, Regular expressions and Command completion. Previous cd commands are available from the history, unless suppressed with special option.
Since bash 4.0 if you set option autocd (by default it is off):
shopt -s autocd
In this case you can type the name of directory without prefixing it with it cd. If you name directories with the first upper case letter that can save you a lot keystrokes.
Now you probably syspect that cd is very complex command. And that is true because the environment in which it operates is so complex. See Sysadmin Horror Stories. some of them involve mistyped, or misunderstood cd command.
If you still have some doubts that cd is a non-trivial command please try to do the following experiment:
ln -s /etc/sysconfig /Fav/sysconf
Now compare the behaviour of the system with your expectations. Did you expect that cd will follow symlink back? To do so you need that command maintain some internal stack of visited directories and remember from which directory you come, because in no way /Fav is the parent directory of /etc/sysconfig.
There are several important shortcuts (see Advanced Unix filesystem navigation for details)
cd ~ # cd to home directory
cd # same thing
cd - # change to previous directory (see also pushd and popd directory stack commands)
cd /etc # change to absolute path
TIP:
alias cdp `cd \!* && pwd'
alias cdl `cd \!* && ls'
cd mypath # change to relative path.
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If CDPATH environment variable is defined, then all directories in that path will be searched for the subdirectory when a relative cd is executed:
> export CDPATH=~/docs > cd a_doc_subdir # will work even when not in ~/docsYou can also use regular expressions in specifying the directory, for example
cd /usr/l*/b*
Standard Wildcards (globbing patterns, see Regular expresstion for details)Standard wildcards (also known as globbing patterns) are used by various command line utilities to work with multiple files. For more information on standard wildcards (globbing patterns) refer to the manual page by typing:
man 7 glob
- ? (question mark)
- this can represent any single character. If you specified something at the command line like "hd?" GNU/Linux would look for hda, hdb, hdc and every other letter/number between a-z, 0-9.
- * (asterisk)
- this can represent any number of characters (including zero, in other words, zero or more characters). If you specified a "cd*" it would use "cda", "cdrom", "cdrecord" and anything that starts with "cd" also including "cd" itself. "m*l" could by mill, mull, ml, and anything that starts with an m and ends with an l.
- [ ] (square brackets)
- specifies a range. If you did m[a,o,u]m it can become: mam, mum, mom if you did: m[a-d]m it can become anything that starts and ends with m and has any character a to d in-between. For example, these would work: mam, mbm, mcm, mdm. This kind of wildcard specifies an "or" relationship (you only need one to match).
- { } (curly brackets)
- terms are separated by commas and each term must be the name of something or a wildcard. This wildcard will copy anything that matches either wildcard(s), or exact name(s) (an "or" relationship, one or the other).
For example, this would be valid:
cp {*.doc,*.pdf} ~This will copy anything ending with .doc or .pdf to the users home directory. Note that spaces are not allowed after the commas (or anywhere else).
- [!]
- This construct is similar to the [ ] construct, except rather than matching any characters inside the brackets, it'll match any character, as long as it is not listed between the [ and ]. This is a logical NOT. For example rm myfile[!9] will remove all myfiles* (ie. myfiles1, myfiles2 etc) but won't remove a file with the number 9 anywhere within it's name.
- \ (backslash)
- is used as an "escape" character, i.e. to protect a subsequent special character. Thus, "\\" searches for a backslash. Note you may need to use quotation marks and backslash(es).
The name of the current directory in which you are working is probably the most basic piece of information about your current environment. You can use the pwd (print current directory) command to show the name of your current (working) directory.
On a UNIX system, files are stored in various directories. At any given time, just one of these directories is your current working directory. And your shell commands affect the files and subdirectories in this working area. When you log on to the system, the current directory is your home directory, where you have full rights to do whatever you want to the files and subdirectories there. You can move from directory to directory using the cd command, discussed in a later section in this chapter. It is generally a good idea to make sure that you have landed in the desired directory before you start executing other commands.
CAUTION
Because UNIX filenames are case sensitive, it is possible--although not a good idea--to have one directory called Projects and another called projects. It is an easy mistake to move to the projects directory when you really want the Projects directory. Therefore, it is good practice to use the pwd command to verify that you are in the right directory before you start deleting any files. Better yet, establish a naming convention for your directories. For example, some people use uppercase letters for directory names and lowercase letters for all regular filenames.
Immediately after logging in, you're placed in your home directory. Let's say that your home directory is /usr/home/genuser. If you execute the pwd command immediately after logging in, then /usr/home/genuser is displayed:
% pwd /usr/home/genuser %
TIP: To help identify the directory you are currently in, you can modify your shell prompt to include the current directory name. For example, in C shell:
% set prompt="´pwd´ %"
includes the name of your working directory as part of the shell prompt, and the prompt looks something like this:
/usr/home/peter %
SEE "Shell Variables," p. 163
The cd (change directory) command changes the current working directory to the named directory. For example:
% pwd /usr/home/peter % cd /usr/home/sally % pwd /usr/home/sally
CAUTION
If you are familiar with DOS, you will find the cd command works exactly the same way in UNIX with two exceptions. In DOS, if you don't specify a directory name when you give the cd command, the current working directory's name is displayed (just like the UNIX pwd command). However, in UNIX, if you don't specify a directory name when you give the cd command, the new directory will be your home directory. The other exception is the use of slash ("/") versus backslash ("\") in the directory path as explained in the following Note.NOTE: You will no doubt notice by now that UNIX directory paths are specified using the forward slash ("/") rather than the backslash ("\") you're so accustomed to in DOS. Don't use the backslash lightly because backslashes in UNIX have special meaning. A backslash stops the shell from giving a special character (known as a metacharacter), such as "*", its special meaning (wildcard, in this case). See the "Special Characters" section later in this chapter for more information.
TIP: You can create an alias for cd that prints your current directory name after you have changed directory. Place the command:
alias cd `cd \!*;pwd'
in the .cshrc file, if you are using the C shell. If the UNIX shell you are using doesn't support aliases, you can create a shell script instead.
The pathname argument to cd may be either an absolute pathname (as shown in the preceding example) or a relative pathname, which is shown in the following example:
% pwd /etc/home/sally % cd ../peter % pwd /etc/home/peter % cd Projects/UNIX.Book % pwd /etc/home/peter/Projects/UNIX.Book
The double dots ("..", a pseudonym for the parent directory) in the first cd command moves the working directory "up one level" and then "down" to a child directory called peter; you can move up multiple levels in the directory tree by specifying multiple ".." in the pathname (for example, cd ../.. moves you up two levels). The second cd command makes the current directory the child directory named UNIX.Book of the child directory named Projects. Note that the second cd path starts where the first one finished.
NOTE: Although ".." is the pseudonym for the parent directory, "." is the pseudonym for the current directory. You may already be familiar with them from using DOS--DOS "borrowed" this naming convention from UNIX.
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The UNIX change directory (cd) command is very useful for navigating in your Oracle directory structure. The cd command without any arguments takes you to the location of your UNIX home directory. The UNIX home directory is specified in the /etc/passwd file and defines where you will be immediately after a UNIX logon.
sting*testc1-/u01/app/oracle/admin/testc1/pfile
>cdsting*testc1-/export/home/oracle
>When you give cd a directory location, you are transferred to that location. In this example, we transfer to the $ORACLE_HOME/rdbms/admin directory:
sting*testc1-/export/home/oracle
>cd $ORACLE_HOME/rdbms/adminsting*testc1-/u01/app/oracle/product/8.1.7_64/rdbms/admin
>UNIX also has a very handy cd argument for switching back-and-forth between two directories. In this example, we use the cd – command to bounce back-and-forth from the pfile directory and the /etc directory:
sting*testc1-/u01/app/oracle/admin/testc1/pfile
>cd /etcsting*testc1-/etc
>cd -
/u01/app/oracle/admin/testc1/pfilesting*testc1-/u01/app/oracle/admin/testc1/pfile
>cd -
/etcsting*testc1-/etc
>You can also use the cd .. command to go up one level in your directory tree. In this example, we navigate from the pfile directory where the init.ora file is located to the bdump directory where the Oracle alert log is located (Figure 1-4).
Figure 4: The OFA Tree and cd navigation
sting*testc1-/u01/app/oracle/admin/testc1/pfile
>cd ../bdumpsting*testc1-/u01/app/oracle/admin/testc1/bdump
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