Linux 版 (精华区)
发信人: netiscpu (说不如做), 信区: Linux
标 题: [B] Red Hat Linux Unleashed (10)
发信站: 紫 丁 香 (Sat Jul 25 03:09:43 1998), 转信
Using bash
_________________________________________________________________
o Shells in a Nutshell
# What Is a Shell?
# How the Shell Gets Started
# The Most Common Shells
o The Bourne Again Shell
# Command-Line Completion
# Wildcards
# Command History
# Aliases
# Input Redirection
# Output Redirection
# Pipelines
# Prompts
# Job Control
o Customizing bash
o bash Command Summary
o bash Variables
o Summary
_________________________________________________________________
10
Using bash
This chapter looks at the shells in a little more detail. You'll start
with bash (Bourne Again Shell), the default shell used by Linux and
the most popular shell for new users. In this chapter you will learn
* What a shell is
* The most common shells used in Linux
* Command-line completion and wildcards
* Command history and aliases
* Redirection and pipes
* Changing prompts
* Job control
* How to customize your bash shell
You will also look at the most commonly used bash commands and the
environment variables bash uses. By the end of this chapter, you
should be able to work faster and more efficiently with bash.
Shells in a Nutshell
What is a shell, anyway? It seems to be a word used all the time in
Linux, but the exact meaning is vague for many new users (and some
veterans). This section explains exactly what a shell program is and
why it is so important when using Linux.
What Is a Shell?
The shell is a program used to interface between you (the user) and
Linux (or, more accurately, between you and the Linux kernel). Figure
10.1 illustrates the relationship between the user, the shell, and the
Linux kernel. Every command you type at a prompt on your screen is
interpreted by the shell, then passed to the Linux kernel.
Figure 10.1. The relationship between the user and the shell.
______________________________________________________________
NOTE: If you are familiar with MS-DOS, you will recognize this
relationship as almost identical to the relationship between a DOS
user and the COMMAND.COM program. The only real difference is that
in the DOS world, no distinction is made between the COMMAND.COM
program and DOS (or to be more accurate, the DOS kernel).
______________________________________________________________
The shell is a command-language interpreter. It has its own set of
built-in shell commands. The shell can also make use of all of the
Linux utilities and application programs that are available on the
system.
Whenever you enter a command it is interpreted by the Linux shell. For
example, in earlier chapters when you were introduced to the Linux
file- and directory-manipulation commands, all of the sample commands
entered at the command prompt were interpreted by whichever Linux
shell you were using.
Some of the commands, such as the print working directory (pwd)
command, are built into the Linux bash shell. Other commands, such as
the copy command (cp) and the remove command (rm), are separate
executable programs that exist in one of the directories in the
filesystem. As the user, you don't know (or probably care) if the
command is built into the shell or is a separate program. Figure 10.2
shows how the shell performs this command interpretation.
Figure 10.2. Command interpretation by the shell.
Figure 10.2 illustrates the steps that the shell takes to figure out
what to do with user commands. It first checks to see if the command
is one of its own built-in commands (like cd or pw. If the command is
not one of these, the shell checks to see if it is an application
program. Application programs can be utility programs that are part of
Linux, such as ls and rm, or they can be application programs that are
either purchased commercially, such as xv, or available as public
domain software, such as ghostview.
The shell tries to find these application programs by looking in all
of the directories that are in your search path. The path is a list of
directories where executable programs can be found. If the command
that was entered is not an internal shell command and it is not an
executable file in your path, an error message will be displayed.
As the last step in a successful command, the shell's internal
commands and all of the application programs are eventually broken
down into system calls and passed to the Linux kernel.
Another important aspect of the shell is that it contains a very
powerful interpretive programming language. This language is similar
in function to the MS-DOS interpreted language, but is much more
powerful. The shell programming language supports most of the
programming constructs found in high-level languages, such as looping,
functions, variables, and arrays.
The shell programming language is easy to learn, and once known it
becomes a very powerful programming tool. Any command that can be
typed at the command prompt can also be put into a executable shell
program. This means that the shell language can be used to simplify
repetitive tasks. See Chapter 13, "Shell Programming," for more
information on shell programming.
How the Shell Gets Started
Earlier in this chapter you learned that the shell is the main method
by which a user interacts with the Linux kernel. But how does this
program get initialized to do so? The shell is started after you
successfully log into the system, and it continues to be the main
method of interaction between the user and the kernel until you log
out.
Each user on your system has a default shell. The default shell for
each user is specified in the system password file, called
/etc/passwd. The system password file contains, among other things,
each person's user ID, an encrypted copy of each user's password, and
the name of the program to run immediately after a user logs into the
system. The program specified in the password file does not have to be
one of the Linux shells, but it almost always is.
The Most Common Shells
Several different kinds of shells are available on Linux and UNIX
systems. The most common are the Bourne shell (called sh), the C shell
(csh), and the Korn shell (ksh). Each of these three shells has its
own advantages and disadvantages.
The Bourne shell was written by Steven Bourne. It is the original UNIX
shell and is available on every UNIX system in existence. The Bourne
shell is considered to be very good for UNIX shell programming, but it
does not handle user interaction as well as some of the other shells
available.
The C shell, written by Bill Joy, is much more responsive to user
interaction. It supports features such as command-line completion that
are not in the Bourne shell. The C shell's programming interface is
thought by many not to be as good as that of the Bourne shell, but it
is used by many C programmers because the syntax of its programming
language is similar to that of the C language. This is also why it is
named the C shell.
The Korn shell (ksh) was written by Dave Korn. He took the best
features of both the C shell and the Bourne shell and combined them
into one that is completely compatible with the Bourne shell. ksh is
efficient and has both a good interactive interface and a good
programming interface.
______________________________________________________________
NOTE: There are many quality reference books about the Bourne, C,
and Korn shells. If you want to use these shells instead of the
three shells discussed in this and the next two chapters, you may
want to find a good reference book on the particular shell you
prefer. Because the shells included with Linux are used by most
people, we will concentrate on those.
______________________________________________________________
In addition to these shells, many other shell programs took the basic
features from one or more of the existing shells and combined them
into a new version. The three newer shells that will be discussed in
this book are tcsh (an extension of csh), the Bourne Again Shell
(bash, an extension of sh), and the Public Domain Korn Shell (pdksh,
an extension of ksh). bash is the default shell on most Linux systems.
The Bourne Again Shell
The Bourne Again Shell (bash), as its name implies, is an extension of
the Bourne shell. bash is fully backward-compatible with the Bourne
shell, but contains many enhancements and extra features that are not
present in the Bourne shell. bash also contains many of the best
features that exist in the C and Korn shells. bash has a very flexible
and powerful programming interface, as well as a user-friendly command
interface.
Why use bash instead of sh? The biggest drawback of the Bourne shell
is the way that it handles user input. Typing commands into the Bourne
shell can often be very tedious, especially if you are using it on a
regular basis and typing in a large number of commands. bash provides
several features that make entering commands much easier.
Command-Line Completion
Often when you enter commands into bash (or any other shell), the
complete text of the command is not necessary in order for the shell
to be able to determine what you want it to do. For example, assume
that the current working directory contains the following files and
subdirectories:
News/ bin/ games/ mail/ samplefile test/
If you want to change directories from the current working directory
to the test subdirectory, you would enter the command
cd test
Although this command will work, bash enables you to accomplish the
same thing in a slightly different way. Since test is the only file in
the directory that begins with the letter t, bash should be able to
figure out what you want to do after you type in the letter t alone:
cd t
After the letter has been typed, the only thing that you could be
referring to is the test subdirectory. To get bash to finish the
command for you, press the Tab key:
cd t<tab>
When you do this, bash finishes the command for you and displays it on
the screen. The command doesn't actually execute until you press the
Enter key to verify that the command bash came up with is the command
that you really intended.
For short commands like this, you might not see very much value in
making use of command-line completion. Using this feature may even
slow you down when typing short commands. After you get used to using
command-line completion, though, and when the commands that you are
entering get a little longer, you will wonder how anyone lived without
this feature.
So what happens if more than one file in the directory begins with the
letter t? It would seem that this would cause a problem if you wanted
to use command-line completion. Let's see what happens when you have
the following directory contents:
News/ bin/ mail/ samplefile test/ tools/ working/
Now you have two files in the directory that start with the letter t.
Assuming that you still want to cd into the test subdirectory, how do
you do it using command-line completion? If you type cd t<tab> as you
did before, bash will not know which subdirectory you want to change
to because the information you have given is not unique.
If you try to do this, bash will beep to notify you that it does not
have enough information to complete the command. After beeping, bash
will leave the command on the screen as it was entered. This enables
you to enter more information without retyping what was already typed.
In this case, you only need to enter an e and press the Tab key again.
This will give bash enough information to complete the command on the
command line for you to verify:
cd test
If instead you decided that you want to cd into the tools
subdirectory, you could have typed
cd to<tab>
This would also give bash enough information to complete the command.
Whenever you press the Tab key while typing a command, bash will try
to complete the command for you. If it can't complete the command, it
will fill in as much as it can and then beep, notifying you that it
needs more information. You can then enter more characters and press
the Tab key again, repeating this process until bash returns the
desired command.
Wildcards
Another way that bash makes typing commands easier is by enabling
users to use wildcards in their commands. The bash shell supports
three kinds of wildcards:
* matches any character and any number of characters.
? matches any single character.
[...] matches any single character contained within the brackets.
The * wildcard can be used in a manner similar to command-line
completion. For example, assume the current directory contains the
following files:
News/ bin/ games/ mail/ samplefile test/
If you want to cd into the test directory, you could type cd test, or
you could use command-line completion:
cd t<tab>
This causes bash to complete the command for you. Now there is a third
way to do the same thing. Because only one file begins with the letter
t, you could also change to the directory by using the * wildcard. You
could enter the following command:
cd t*
The * matches any character and any number of characters, so the shell
will replace the t* with test (the only file in the directory that
matches the wildcard pattern).
This will work reliably only if there is one file in the directory
that starts with the letter t. If more than one file in the directory
starts with the letter t, the shell will try to replace t* with the
list of filenames in the directory that match the wildcard pattern and
the cd command will cd into the first directory in this list. This
will end up being the file that comes first alphabetically, and may or
may not be the intended file.
A more practical situation in which to use the * wildcard is when you
want to execute the same command on multiple files that have similar
filenames. For example, assume the current directory contains the
following files:
ch1.doc ch2.doc ch3.doc chimp config mail/ test/ tools/
If you wanted to print all of the files that have a .doc extension,
you could do so easily by entering the following command:
lpr *.doc
In this case, bash will replace *.doc with the names of all of the
files in the directory that match that wildcard pattern. After bash
performed this substitution, the command that would be processed would
be:
lpr ch1.doc ch2.doc ch3.doc
The lpr command would be invoked with the arguments of ch1.doc,
ch2.doc, and ch3.doc.
______________________________________________________________
NOTE: Given the directory contents used in the previous example,
there are several ways to print all of the files that have a .doc
extension. All of the following commands would also work:
lpr *doc
lpr *oc
lpr *c
______________________________________________________________
The ? wildcard functions in an identical way to the * wildcard except
that the ? wildcard only matches a single character. Using the same
directory contents shown in the previous example, the ? wildcard could
be used to print all of the files with the .doc extension by entering
the following command:
lpr ch?.doc
The [...] wildcard enables you to specify certain characters or ranges
of characters to match. To print all of the files in the example that
have the .doc extension using the [...] wildcard, you would enter one
of the following two commands:
lpr ch[123].doc
Using a command to specify a range of characters, you would enter
lpr ch[1-3].doc
Command History
bash also supports command history. This means that bash keeps track
of a certain number of previous commands that have been entered into
the shell. The number of commands is given by a shell variable called
HISTSIZE. For more information on HISTSIZE, see the section "bash
Variables" later in this chapter.
bash stores the text of the previous commands in a history list. When
you log into your account, the history list is initialized from a
history file. The filename of the history file can be set using the
HISTFILE bash variable. The default filename for the history file is
.bash_history. This file is usually located in your home directory.
(Notice that the file begins with a period. This means that the file
is hidden and will only appear in a directory listing if you use the
-a or -A option of the ls command.).
Just storing previous commands into a history file is not all that
useful, so bash provides several ways of recalling them. The simplest
way of using the history list is with the up- and down-arrow keys,
which scroll through the commands that have been previously entered.
Pressing the up-arrow key will cause the last command that was entered
to appear on the command line. Pressing the up-arrow key again will
put the command previous to that one on the command line, and so on.
If you move up in the command buffer past the command that you wanted,
you can also move down the history list a command at a time by
pressing the down-arrow key. (This is the same process used by the DOS
doskey utility.)
The command displayed on the command line through the history list can
be edited, if needed. bash supports a complex set of editing
capabilities that are beyond the scope of this book, but there are
simple ways of editing the command line for small and easy changes.
You can use the left and right arrow keys to move along the command
line. You can insert text at any point in the command line, and can
also delete text by using the Backspace or Delete key. Most users
should find these simple editing commands sufficient.
______________________________________________________________
NOTE: The complex set of editing commands that bash offers are
similar to the commands used in the emacs and vi text editors.
______________________________________________________________
Another method of using the history file is to display and edit the
list using the history and fc (fix command) commands built into bash.
The history command can be invoked using two different methods. The
first method uses the command
history [n]
When the history command is used with no options, the entire contents
of the history list are displayed. The list that is displayed
on-screen might resemble the following sample list:
1 mkdir /usr/games/pool
2 cp XpoolTable-1.2.linux.tar.z /usr/games/pool
3 cd /usr/games/pool/
4 ls
5 gunzip XpoolTable-1.2.linux.tar.z
6 tar -xf XpoolTable-1.2.linux.tar
7 ls
8 cd Xpool
9 ls
10 xinit
11 exit
12 which zip
13 zip
14 more readme
15 vi readme
16 exit
Using the n with the history command causes the only last n lines in
the history list to be shown. So, for example, history 5 shows only
the last five commands.
The second method of invoking the history command is used to modify
the contents of the history file, or the history list. The command has
the following command-line syntax:
history [-r|w|a|n] [filename]
In this form, the -r option tells the history command to read the
contents of the history file and use them as the current history list.
The -w option will cause the history command to write the current
history list to the history file (overwriting what is currently in the
file). The -a option appends the current history list to the end of
the history file. The -n option causes the lines that are in the
history file to be read into the current history list.
All of the options for the second form of the history command can use
the filename option as the name of the history file. If no filename is
specified, the history command will use the value of the HISTFILE
shell variable.
The fc command can be used in two different ways to edit the command
history. In the first way, the fc command would be entered using the
following command-line syntax:
fc [-e editor_name] [-n] [-l] [-r] [first] [last]
where all options given in braces are optional. The -e editor name
option is used to specify the text editor to be used for editing the
commands. The first and last options are used to select a range of
commands to take out of the history list. first and last can refer
either to the number of a command in the history list or to a string
that fc will try to find in the history list.
The -n option is used to suppress command numbers when listing the
history commands. The -r option lists the matched commands in reverse
order. The -l command lists the matched commands to the screen. In all
cases except when the -l command option is used, the matching commands
will be loaded into a text editor.
______________________________________________________________
NOTE: The text editor used by fc is found by taking the value of
editor name if the -e editor name option is used. If this option
was not used, fc uses the editor specified by the variable FCEDIT.
If this variable does not exist, fc will use the value of the
EDITOR variable. Finally, if none of these variables exists, the
editor that will be chosen is vi, by default.
______________________________________________________________
Aliases
Another way that bash makes life easier for you is by supporting
command aliases. Command aliases are commands that the user can
specify. Alias commands are usually abbreviations of other commands,
designed to save keystrokes.
For example, if you are entering the following command on a regular
basis, you might be inclined to create an alias for it to save
yourself some typing:
cd /usr/X11R6/lib/X11/config
Instead of typing this command every time you wanted to go to the
sample-configs directory, you could create an alias called goconfig
that would cause the longer command to be executed. To set up an alias
like this you must use the bash alias command. To create the goconfig
alias, enter the following command at the bash prompt:
alias goconfig='cd /usr/X11R6/lib/X11/configs
Now, until you exit from bash, the goconfig command will cause the
original, longer command to be executed as if you had just typed it.
If you decide after you have entered an alias that you did not need
it, you can use the bash unalias command to delete the alias:
unalias goconfig
There are a number of useful aliases that most users find helpful.
These can be written in a file that you execute when you log in, to
save you from typing them each time. Some aliases that you might want
to define are the following:
* alias ll='ls -l'
* alias log='logout'
* alias ls='ls -F'
If you are a DOS user and are used to using DOS file commands, you can
use the alias command to define the following aliases so that Linux
behaves like DOS:
* alias dir='ls'
* alias copy='cp'
* alias rename='mv'
* alias md='mkdir'
* alias rd='rmdir'
______________________________________________________________
NOTE: When defining aliases, you can't include spaces on either
side of the equal sign, or the shell can't properly determine what
you want to do. Quotation marks are necessary only if the command
within them contains spaces or other special characters.
______________________________________________________________
If you enter the alias command without any arguments, it will display
all of the aliases that are already defined on-screen. The following
listing illustrates a sample output from the alias command:
alias dir='ls'
alias ll='ls -l'
alias ls='ls -F'
alias md='mkdir'
alias net='term < /dev/modem > /dev/modem 2> /dev/null&'
alias rd='rmdir'
Input Redirection
Input redirection is used to change the source of input for a command.
When a command is entered in bash, the command is expecting some kind
of input in order to do its job. Some of the simpler commands must get
all of the information that they need passed to them on the command
line. For example, the rm command requires arguments on the command
line. You must tell rm the files that you want it to delete on the
command line, or it will issue a prompt telling you to enter rm -h for
help.
Other commands require more elaborate input than a simple directory
name. The input for these commands can be found in a file. For
example, the wc (word count) command counts the number of characters,
words, and lines in the input that was given to it. If you just type
wc <enter> at the command line, wc waits for you to tell it what it
should be counting. There will be a prompt on the command line asking
for more information, but because the prompt is sometimes not easily
identifiable, it will not necessarily be obvious to you what is
happening. (It might actually appear as though bash has died, because
it is just sitting there. Everything that you type shows up on-screen,
but nothing else appears to be happening.)
What is actually occurring is that the wc command is collecting input
for itself. If you press Ctrl-D, the results of the wc command will be
written to the screen. If you enter the wc command with a filename as
an argument, as shown in the following example, wc will return the
number of characters, words, and lines that are contained in that
file:
wc test
11 2 1
Another way to pass the contents of the test file to wc is to redirect
the input of the wc command from the terminal to the test file. This
will result in the same output. The < symbol is used by bash to mean
"redirect the input to the current command from the specified file."
So, redirecting wc's input from the terminal to the test file can be
done by entering the following command:
wc < test
11 2 1
Input redirection is not used all that often because most commands
that require input from a file have the option to specify a filename
on the command line. There are times, however, when you will come
across a program that will not accept a filename as an input
parameter, and yet the input that you want to give exists in a file.
Whenever this situation occurs, you can use input redirection to get
around the problem.
Output Redirection
Output redirection is more commonly used than input redirection.
Output redirection enables you to redirect the output from a command
into a file, as opposed to having the output displayed on-screen.
There are many situations in which this can be useful. For example, if
the output of a command is quite large and will not fit on the screen,
you might want to redirect it to a file so that you can view it later
using a text editor. There also may be cases where you want to keep
the output of a command to show to someone else, or so you can print
the results. Finally, output redirection is also useful if you want to
use the output from one command as input for another. (There is an
easier way to use the output of one command as input to a second
command. This is shown in the "Pipelines" section in this chapter.)
Output redirection is done in much the same way as input redirection.
Instead of using the < symbol, the > symbol is used.
______________________________________________________________
NOTE: The best way to remember which symbol is input or output
redirection is to think of the < as a funnel that is funneling
input into the command (because the command receiving the input
will be on the left-hand side of the <) and the > as a funnel that
is funneling the output from the command into a file.
______________________________________________________________
As an example of output redirection, you can redirect the output of
the ls command into a file named directory.out using the following
command:
ls > directory.out
Pipelines
Pipelines are a way to string together a series of commands. This
means that the output from the first command in the pipeline is used
as the input to the second command in the pipeline. The output from
the second command in the pipeline is used as input to the third
command in the pipeline, and so on. The output from the last command
in the pipeline is the output that you will actually see displayed
on-screen (or put in a file if output redirection was specified on the
command line).
You can tell bash to create a pipeline by typing two or more commands
separated by the vertical bar or pipe character, |. The following
example illustrates the use of a pipeline:
cat sample.text | grep "High" | wc -l
This pipeline would take the output from the cat command (which lists
the contents of a file) and send it into the grep command. The grep
command searches for each occurrence of the word High in its input.
The grep command's output would then consist of each line in the file
that contained the word High. This output is then sent to the wc
command. The wc command with the -l option prints the number of lines
contained in its input.
To show the results on a real file, suppose the contents of
sample.text was
Things to do today:
Low: Go grocery shopping
High: Return movie
High: Clear level 3 in Alien vs. Predator
Medium: Pick up clothes from dry cleaner
The pipeline would return the result 2, indicating that you had two
things of high importance to complete today:
cat sample.text | grep "High" | wc -l
2
Prompts
bash has two levels of user prompt. The first level is what you see
when bash is waiting for a command to be typed. (This is what you
normally see when you are working with bash.)
The default first-level prompt is the $ character. If you do not like
the $ character as the prompt, or you would prefer to customize your
prompt, you can do so by setting the value of the PS1 bash variable.
For example:
PS1="Please enter a command"
sets the bash shell prompt to the specified string.
The second level of prompt is displayed when bash is expecting more
input from you in order to complete a command. The default for the
second level prompt is >. If you want to change the second-level
prompt, you can set the value of the PS2 variable, as in
PS2="I need more information"
In addition to displaying static character strings in the command
prompts (as in the two preced-ing examples), you can also use some
predefined special characters. These special characters place things
such as the current time into the prompt. Table 10.1 lists the most
commonly used special-character codes.
Table 10.1. Prompt special character codes.
Character Meaning
\! Displays the history number of this command.
\# Displays the command number of the current command.
\$ Displays a $ in the prompt unless the user is root. When the user
is root, it displays a #.
\\ Displays a backslash.
\d Displays the current date.
\h Displays the host name of the computer on which the shell is
running.
\n Prints a newline character. This will cause the prompt to span more
than one line.
\nnn Displays the character that corresponds to the octal value of the
number nnn.
\s The name of the shell that is running.
\t Displays the current time.
\u Displays the username of the current user.
\W Displays the base name of the current working directory.
\w Displays the current working directory.
These special characters can be combined into several useful prompts
to provide you with information about where you are. (They can be
combined in very grotesque ways, too!) Several examples of setting the
PS1 prompt are:
PS1="\t"
This would cause the prompt to have the following appearance (there
would not be a space after the prompt):
02:16:15
The prompt string
PS1=\t
would cause the prompt to have the following appearance:
t
This shows the importance of including the character sequence in
quotation marks. The prompt string
PS1="\t\\ "
will cause the prompt to look like this:
02:16:30\
In this case, there would be a space following the prompt because
there was a space within the quotation marks.
Job Control
Job control refers to the ability to control the execution behavior of
a currently running process. Specifically, you can suspend a running
process and cause it to resume running at a later time. bash keeps
track of all of the processes that it started (as a result of user
input), and you can suspend a running process or restart a suspended
one at any time during the life of that process.
Pressing Ctrl-Z suspends a running process. The bg command restarts a
suspended process in the background, whereas the fg command restarts a
process in the foreground.
These commands are most often used when a user wants to run a command
in the background but by accident starts it in the foreground. When a
command is started in the foreground, it locks the shell from any
further user interaction until the command completes execution. This
is usually no problem because most commands only take a few seconds to
execute. If the command you are running is going to take a long time,
though, you would typically start the command in the background so
that you could continue to use bash to enter other commands in the
foreground.
For example, if you started the command find / -name "test" > find.out
(which will scan the entire filesystem for files named test and store
the results in a file called find.out) in the foreground, your shell
may be tied up for many seconds or even minutes, depending on the size
of the filesystem and the number of users on the system. If you had
issued this command and wanted to continue executing in the background
so you could use the system again, you would enter the following:
control-z
bg
This would first suspend the find command, then restart it in the
background. The find command would continue to execute, and you would
have bash back again.
Customizing bash
Many ways of customizing bash have already been described in this
chapter. Until now, the changes that you made affected only the
current bash session. As soon as you quit, all of the customizations
that you made will be lost. You can make the customizations more
permanent by storing them in a bash initialization file.
You can put any commands that you want to be executed each time bash
is started into this initialization file. Commands that are typically
found in this file are alias commands and variable initializations.
The bash initialization file is named profile. Each user who uses bash
has a .profile file in his home directory. This file is read by bash
each time it starts, and all of the commands contained within it are
executed.
The following code shows the default .profile file. This file is
located in the /etc directory and is read when you start bash. If you
want to add your own customizations to bash, you must copy this file
into your home directory (if it is not already there) and call it
.profile.
______________________________________________________________
NOTE: Some setup programs make a copy of the .profile file in your
home directory for you automatically when they create your login.
However, not all routines do this, so you should check your home
directory first. Remember that all files starting with a period are
hidden and can only be displayed with the ls -A or ls -a command.
______________________________________________________________
# commands common to all logins
export OPENWINHOME=/usr/openwin
export MINICOM="-c on"
export MANPATH=/usr/local/man:/usr/man/preformat:/usr/man:/X11/man:/usr/openwin
/man
export HOSTNAME="'cat /etc/HOSTNAME'"
PATH="$PATH:/usr/X11/bin:$OPENWINHOME/bin:/usr/games:."
LESS=-MM
# I had problems using 'eval test' instead of 'TERM=', but you might want to
# try it anyway. I think with the right /etc/termcap it would work great.
# eval 'tset -sQ "$TERM"'if [ "$TERM" = "" -o "$TERM" = "unknown"]; then
TERM=linux
fi
#PS1=''hostname':'pwd'# '
if [ "$SHELL" = "/bin/pdksh" -o "$SHELL" = "/bin/ksh" ]; then
PS1="! $"
elif [ "$SHELL" = "/bin/zsh" ]; then
PS1="%m:%~%# "
elif [ "$SHELL" = "/bin/ash" ]; then
PS1="$ "
else
PS1='\h:\w\$ '
fi
PS2='> '
ignoreeof=10
export PATH DISPLAY LESS TERM PS1 PS2 ignoreeof
umask 022
# set up the color-ls environment variables:
if [ "$SHELL" = "/bin/zsh" l; then
eval 'dircolors -z'
elif [ "$SHELL" = "/bin/ash" l; then
eval 'dircolors -s'
else
eval 'dircolors -b'
fi
echo
fortune
echo
export TAPE="/dev/nftape"
bash Command Summary
Here are some of the most useful commands built into the bash shell:
alias: Used to set bash aliases (command nicknames that can be
defined by the user).
bg: Background command. Forces a suspended process to continue to
execute in the background.
cd: Change working directory. This command changes the current
working directory to the directory specified as an argument.
exit: Terminates the shell.
export: Causes the value of a variable to be made visible to all
subprocesses that belong to the current shell.
fc: Fix command. Used to edit the commands in the current history
list.
fg: Foreground command. Forces a suspended process to continue to
execute in the foreground.
help: Displays help information for bash built-in commands.
history: Brings up a list of the last n commands that were
entered at the command prompt, where n is a configurable
variable specifying the number of commands to remember.
kill: Used to terminate another process.
pwd: Print working directory. Prints the directory in which the
user is currently working.
unalias: Used to remove aliases that have been defined using the
alias command.
bash has many more commands than are listed here, but these are the
most frequently used ones. To see the other commands bash offers and
for more details of the commands listed, refer to the bash man page
(type man bash).
bash Variables
Here are some of the most useful bash variables, including the
variable name and a brief description:
EDITOR, FCEDIT: The default editor for the fc bash command.
HISTFILE: The file used to store the command history.
HISTSIZE: The size of the history list.
HOME: The HOME directory of the current user
OLDPWD: The previous working directory (the one that was current
before the current directory was entered).
PATH: The search path that bash uses when looking for executable
files
PS1: The first-level prompt that is displayed on the command line
PS2: The second-level prompt that is displayed when a command is
expecting more input
PWD: The current working directory
SECONDS: The number of seconds that have elapsed since the
current bash session was started
bash has many more variables than are listed here, but the most
commonly used ones are shown. To find out what other variables bash
offers, call the man page with the command man bash.
Summary
In this chapter you looked at some of the useful features of the
Bourne Again Shell, bash. You have seen how command completion,
aliasing, and job control can all combine to make you more productive
and efficient when working with bash.
In the next chapter you will look at another popular Linux shell, the
Public Domain Korn Shell (pdksh). It offers many useful features, too,
providing you with a choice of shells.
--
Enjoy Linux!
-----It's FREE!-----
※ 修改:．netiscpu 于 Jul 25 03:45:25 修改本文．[FROM: mtlab.hit.edu.cn]
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