Linux学习笔记

注：本位为Linux系统的学习笔记，内容来自图书《Beginning Linux Programming》

目录

• Get Started
• Shell Programming
  • shell and bash
  • Pipes and Redirection
  • Shell Programming
    • Creating a script
    • Making a Script Executable
  • Shell Syntax
    • Variables
    • Quoting
    • Environment Variables
    • Parameters Variables
    • Conditions

Get Started

• Unix: originally developed at Bell Laboratories, designed in the 1970s.
• Unix-like systems:
  • some available commercially: IBM’s AIX, HP’s HP-UX, and Sun’s Solaris
  • some available for free: FreeBSD and Linux
• Linux: freely distributed implementation of a UNIX-like kernel.
• GNU: stands for the recursive GNU’s Not UNIX
• GPL: GNU General Public License
• softwares from the GNU project under GPL:
  • GCC: The GNU Compiler Collection, containing the GNU C compiler
  • G++: A C++ compiler, included as part of GCC
  • GDB: A source code-level debugger
  • GNU maker: A version of UNIX make
  • Bison: A parser generator compatible with UNIX yacc
  • bash: A command shell
  • GNU Emacs: A text editor and environment
• PATH:
  • /bin, /usr/bin, /usr/local/bin
  • /sbin, /usr/sbin (system administration program)
  • /opt (optional operating system components and third-party applications)
• Header Files
  • provide definitions of constants and declarations for system and library function calls
  • /usr/include
• Library Files
  • collections of precompiled functions
  • standard system libaries: /lib, /usr/lib
  • .a for traditional, static libraries
  • .so for shared libraries
• gcc
  • -o write output to
  • -I use header files in subdirectories or nonstandard places
  • -l
  • -L
• Static libraries
• Shared Libraries
• Getting help: man gcc和info gcc

Shell Programming

shell and bash

• A shell is a program that acts as the interface between you and the Linux system, enabling you to enter commands for the operating system to execute.
• In linux, the standard shell that is always installed as /bin/sh is called bash (the GNU Bourne-Again SHell), from the GNU suite of tools.

Pipes and Redirection

• file descriptor:
  • 0: standard input to a program
  • 1: standard output
  • 2: standard error
• Redirecting Output
  • >: redirect the standard output into a file
  • >>: append the standard output into a file

#分开output和error信息
kill 1234 >killout.txt 2>killerr.txt

#利用>&结合output和error信息
kill 1234 >killouterr.txt 2>&1

#利用/dev/null扔掉输出
kill 1234 >/dev/null 2>&1

• Redirecting Input

more < killout.txt

但是这看起来并没有什么太大的用处。

• Pipes

 ps –xo comm | sort | uniq | grep -v sh | more

Shell Programming

Creating a script

• #: comments
• #!(in the first line): tell the system which program to be used to execute this file. For example, #! /bin/sh is the default shell program.
• commands: any Linux commands referenced by you PATH environment variable
• exit: returns a sensible exit code. 0 denotes success
• file command: check file type

Making a Script Executable

chmod +x script

• chmod: change file modes or Access Control Lists
• chown: change file owner and group
• chgrp: change group

Shell Syntax

Variables

#所有的变量都被当成字符串，且case-sensitive
#数字类的字符串可以用一些utilities转换
#获取变量内容使用$
salutation=Hello
echo $salutation     ##输出“Hello”
# 有空格时，可以用引号
salutation="Yes Dear"
echo $salutation     ##输出“Yes Dear”

salutation=7+5
echo $salutation      ##输出“7+5”

# 使用read命令让用户对变量赋值
read salutation     ##用户输入“Hi”
echo $salutation      ##输出“Hi”

Quoting

myvar=”Hi there”
echo $myvar        ##输出"Hi there"
echo “$myvar”      ##输出"Hi there"
echo ‘$myvar’      ##输出"$myvar" 
echo \$myvar       ##输出"$myvar" 

Environment Variables

Parameters Variables

Conditions

• test or [: the shell’s Boolean check
• condition structure:

## 检查是否存在文件
## test的exit code决定是否继续执行代码
if test -f fred.c
then
## 插入代码
fi

或者

##请注意之间的空格
if [ -f fred.c ]
then
## 插入代码
fi

完整的

if + 条件判断
then
## 插入代码
elif + 条件判断
then
## 插入代码
else
## 插入代码
fi

• condition types: String Comparison，Arithmetic Comparison，File Conditional