# Linux 简介 系统的学习请看 [鸟哥的私房菜](http://cn.linux.vbird.org/linux_basic/linux_basic.php), 入门推荐阅读章节请参考 [a_short_introduction_of_linux.pdf](./a_short_introduction_of_linux.pdf) 的最后几页. ## 文件系统 目录结构 ```bash /-/ |-bin/ |-boot/ |-dev/ |-etc/ |-home/ | |-user1/ | |-user2/ |-lib/ |-media/ |-mnt/ |-opt/ |-proc/ |-root/ |-run/ |-sbin/ |-srv/ |-sys/ |-tmp/ |-usr/ |-var/ ``` ## 获取帮助 通过 man 查看命令的详细信息 ``` man ``` man 手册有多个章节, 通过 `man
` 来查看不同章节的命令的帮助信息. ``` 1 Executable programs or shell commands 2 System calls (functions provided by the kernel) 3 Library calls (functions within program libraries) 4 Special files (usually found in /dev) 5 File formats and conventions, e.g. /etc/passwd 6 Games 7 Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7) 8 System administration commands (usually only for root) 9 Kernel routines [Non standard] ``` ## Shell Shell 是用户和操作系统内核之间的交互接口, 常见的 Shell 有 Bash, zsh, csh, ksh 等. 不同的 shell 有不同的特性, 但是基本的命令是相同的. ### 环境变量 1. PATH 2. HOME 3. PWD 4. USER 5. SHELL 6. TERM 6. LANG ### 常用命令 基本操作 + echo + ls, pwd, cd, pushd, popd + cp, mv, rm, mkdir, touch 获取帮助 + man, info 查看文件 + cat, more, less, head, tail + tee 编辑文件 + nano, vim, emacs 文本处理 + cut, sort, uniq + grep, sed, awk + diff, patch 查找文件与命令 + find, which, locate 参数 + xargs 查看当前登录用户 + who, whoami shell 设置与环境变量 + set, export, unset 修改文件权限 + chmod, chown 查看硬盘使用情况 + df, du 压缩与同步 + tar + rsync + scp, sftp 下载 + wget, curl 查看进程 + top, htop, free + ps, kill ### 重定向与管道 标准输入 (0), 标准输出 (1), 标准错误 (2) 1. `>` 重定向标准输出, `>>` 追加标准输出 ```bash echo 'abc' > a.txt cat a.txt echo 'abc' >> a.txt cat a.txt ``` 2. `2>` 重定向标准错误, `2>>` 追加标准错误 ```bash cat not_a_file 2> b.txt cat b.txt cat not_b_file 2>> b.txt cat b.txt ``` ```bash cat a.txt not_a_file >output.txt 2> error.txt ``` ```bash cat a.txt not_a_file >output.txt 2>&1 ``` 3. 管道 `|` ```bash ls -l | grep 'abc' ``` 4. 了解文件描述符 ### 单行命令 显示内存使用情况 ```bash while true; do free -h; sleep 1; echo -en '\e[3A'; done ``` ## 其他常用工具 ### 终端复用 + screen, tmux ### 版本管理 + git 全局忽略文件: ```bash echo "*.aux" >> ~/.gitignore_global git config --global core.excludesfile ~/.gitignore_global ``` ## 远程登录 Linux 服务器 ### ssh ```bash ssh @ [-p ] ``` ```bash ssh -J xxx@jump-hostname yyy@hostname -p ``` ### ssh 配置文件 通过中间服务器登录 ```bash cat >> ~/.ssh/config << EOF Host workstation Hostname ip-address-or-hostname Port 22 User username IdentityFile ~/.ssh/id_ed25519 ProxyJump someone@proxy.com EOF ``` ```bash ssh workstation ``` ### ssh 免密登录设置 1. 生成密钥对 ```bash ssh-keygen -t ed25519 -C "your-customer-comment" ``` ```bash ssh-keygen -t rsa -b 4096 -C "your-customer-comment" ``` 2. 拷贝公钥到服务器 ```bash ssh-copy-id @ ``` ### Windows 客户端: 1. 客户端 MobaXterm https://mobaxterm.mobatek.net 2. Putty ## `grep` 和正则表达式 一下内容摘自 grep 手册 ```text REGULAR EXPRESSIONS A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions. grep understands three different versions of regular expression syntax: “basic” (BRE), “extended” (ERE) and “perl” (PCRE). In GNU grep there is no difference in available functionality between basic and extended syntaxes. In other implementations, basic regular expressions are less powerful. The following description applies to extended regular expressions; differences for basic regular expressions are summarized afterwards. Perl-compatible regular expressions give additional functionality, and are documented in pcresyntax(3) and pcrepattern(3), but work only if PCRE is available in the system. The fundamental building blocks are the regular expressions that match a single character. Most characters, including all letters and digits, are regular expressions that match themselves. Any meta-character with special meaning may be quoted by preceding it with a backslash. The period . matches any single character. It is unspecified whether it matches an encoding error. Character Classes and Bracket Expressions A bracket expression is a list of characters enclosed by [ and ]. It matches any single character in that list. If the first character of the list is the caret ^ then it matches any character not in the list; it is unspecified whether it matches an encoding error. For example, the regular expression [0123456789] matches any single digit. Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example. To obtain the traditional interpretation of bracket expressions, you can use the C locale by setting the LC_ALL environment variable to the value C. Finally, certain named classes of characters are predefined within bracket expressions, as follows. Their names are self explanatory, and they are [:alnum:], [:alpha:], [:blank:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means the character class of numbers and letters in the current locale. In the C locale and ASCII character set encoding, this is the same as [0-9A-Za-z]. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket expression.) Most meta-characters lose their special meaning inside bracket expressions. To include a literal ] place it first in the list. Similarly, to include a literal ^ place it anywhere but first. Finally, to include a literal - place it last. Anchoring The caret ^ and the dollar sign $ are meta-characters that respectively match the empty string at the beginning and end of a line. The Backslash Character and Special Expressions The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at the edge of a word. The symbol \w is a synonym for [_[:alnum:]] and \W is a synonym for [^_[:alnum:]]. Repetition A regular expression may be followed by one of several repetition operators: ? The preceding item is optional and matched at most once. * The preceding item will be matched zero or more times. + The preceding item will be matched one or more times. {n} The preceding item is matched exactly n times. {n,} The preceding item is matched n or more times. {,m} The preceding item is matched at most m times. This is a GNU extension. {n,m} The preceding item is matched at least n times, but not more than m times. Concatenation Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated expressions. Alternation Two regular expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either alternate expression. Precedence Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole expression may be enclosed in parentheses to override these precedence rules and form a subexpression. Back-references and Subexpressions The back-reference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular expression. Basic vs Extended Regular Expressions In basic regular expressions the meta-characters ?, +, {, |, (, and ) lose their special meaning; instead use the backslashed versions \?, \+, \{, \|, \(, and \). ``` ### Basic (`-G` default) vs Extended (`-E`) Regular Expressions In basic regular expressions the meta-characters `?`, `+`, `{`, `|`, `(`, and `)` lose their special meaning; instead use the backslashed versions `\?`, `\+`, `\{`, `\|`, `\(`, and `\)`. ### Braket 1. Most meta-characters lose their special meaning inside bracket expressions. 2. To include a literal `]` place it first in the list. Similarly, to include a literal `^` place it anywhere but first. 3. Finally, to include a literal `-` place it last. ## Proxy for Linux 1. Enable proxy through dynamic port forwarding in ssh (the sockets proxy port is 5000) ```bash # Replace 'user' with your username and 'hostname' with the remote host address ssh -vv -N -D 5000 user@hostname ``` Then you can set environment variables to route all your terminal traffic through the proxy. ```bash export http_proxy="socks5h://127.0.0.1:5000" export https_proxy="socks5h://127.0.0.1:5000" ``` This will ensure that most command-line tools (such as `wget`, `curl`, `git`, etc.) use the SOCKS5 proxy by default. 1. apt proxy Assume the proxy is on localhost at port 5000, using the SOCKS5 protocol. 1. `-o` option ```bash sudo apt -o Acquire::http::proxy="socks5h://127.0.0.1:5000" update ``` 2. configuration file `/etc/apt/apt.conf` ``` Acquire::http::proxy "socks5h://127.0.0.1:5000/"; Acquire::ftp::proxy "socks5h://127.0.0.1:5000/"; Acquire::https::proxy "socks5h://127.0.0.1:5000/"; ``` 1. curl proxy Use the configuration file `~/.curlrc` or the command line option `-x` ```bash curl -x socks5h://localhost:5000 -L -O ```