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达内UNIX课程学习笔记要点解析

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UNIX操作系统是由美国电话电报公司（AT&T）的贝尔实验室于1969年开发的一个多用户、多任务操作系统。它的设计哲学是简洁和模块化，强调程序之间的接口和独立性。由于其稳定性和效率，UNIX在互联网服务器、嵌入式系统以及企业级应用中得到了广泛的应用。以下是基于提供的文件信息中UNIX相关知识点的详细说明。 ### 1. UNIX的基本概念和历史 #### a. 操作系统简介 UNIX是一种多用户、多任务的操作系统。在多用户环境下，多个用户可以同时使用同一台计算机，而且各个用户之间是相互隔离的，互不影响。多任务指的是操作系统允许多个程序同时运行，操作系统负责资源的分配和管理。 #### b. UNIX的发展历史 UNIX的发展经历了多个阶段，从最初的Version 1到现在的众多变种和衍生系统。最著名的有AT&T开发的System V和加州大学伯克利分校的BSD（Berkeley Software Distribution）。如今流行的UNIX-like系统有Linux、FreeBSD、Mac OS X等。 ### 2. UNIX系统架构 #### a. 内核（Kernel） 内核是UNIX系统的核心部分，它负责管理系统资源，如CPU、内存、设备驱动程序等。内核为上层应用提供了一组系统调用，使得应用程序可以通过这些调用来请求服务。 #### b. Shell和命令行接口 Shell是用户与UNIX系统交互的命令行界面。常见的Shell有Bourne Shell（sh）、C Shell（csh）、Korn Shell（ksh）和Bash等。Shell可以执行用户输入的命令，处理输入输出重定向和管道，以及执行脚本程序。 #### c. 文件系统 UNIX文件系统是一种树状结构，所有文件都包含在这个结构中，被称为目录。UNIX系统将所有事物都视为文件来处理，包括硬件设备、目录和普通文件等。 #### d. 进程管理 UNIX系统中的每个运行程序都是一个进程，系统管理进程的创建、执行、调度和终止。进程间通信可以使用信号、管道、消息队列、共享内存和套接字等方式。 ### 3. UNIX基本命令 #### a. 文件和目录操作命令 - `ls`：列出目录内容 - `cd`：切换目录 - `mkdir`：创建目录 - `rmdir`：删除空目录 - `cp`：复制文件或目录 - `mv`：移动或重命名文件或目录 - `rm`：删除文件或目录 #### b. 文本处理命令 - `cat`：显示文件内容 - `grep`：文本搜索工具 - `awk`：文本分析工具 - `sed`：流编辑器 - `sort`：排序文本行 - `uniq`：报告或删除重复行 #### c. 权限和用户管理命令 - `chmod`：改变文件或目录权限 - `chown`：改变文件或目录的所有者 - `chgrp`：改变文件或目录的组 - `useradd`和`usermod`：添加和修改用户信息 - `passwd`：更改用户密码 #### d. 系统管理命令 - `ps`：显示当前进程状态 - `top`：动态显示系统进程和资源使用情况 - `kill`：向进程发送信号 - `df`：显示磁盘空间使用情况 - `free`：显示内存使用情况 ### 4. UNIX的高级特性 #### a. 管道（Pipes） 管道是UNIX系统中用于进程间通信的一种机制，它允许一个进程的标准输出直接连接到另一个进程的标准输入。 #### b. 重定向 重定向允许用户改变一个命令的标准输入或标准输出。例如，`>`用于重定向标准输出，`<`用于重定向标准输入。 #### c. 信号和进程控制 UNIX提供了一种软件中断机制，称为信号，用于进程间通信或通知进程系统事件。例如，`kill`命令可以向进程发送信号，控制进程行为。 #### d. shell脚本编程 Shell脚本是将命令序列保存在文件中，然后可以像执行普通命令一样执行这些命令序列。Shell脚本编程提供了自动化任务和处理逻辑的能力。 ### 5. UNIX编程接口 UNIX提供了一系列的系统调用和标准库函数，如C语言的标准库，供程序员开发应用程序。这些接口包括文件操作、进程控制、网络通信和用户接口等。 ### 结语 以上所述仅为UNIX系统核心知识点的粗略介绍，实际掌握UNIX系统需要深入学习其设计哲学、系统架构、命令行工具、系统编程接口等多个方面。通过不断地实践和应用，可以充分发掘出UNIX系统的潜力，满足各种复杂和高效的计算需求。

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2009 达内Unix学习笔记

集合了 所有的 Unix命令大全 登陆服务器时输入 公帐号 openlab-open123 telnet 192.168.0.23 自己帐号 sd08077-you0 ftp工具 192.168.0.202 tools-toolss 老师测评网址 http://172.16.0.198:8080/poll/ 各个 shell 可互相切换 ksh:$ sh:$ csh:guangzhou% bash:bash-3.00$ 一、注意事项 命令和参数之间必需用空格隔开，参数和参数之间也必需用空格隔开。 一行不能超过256个字符；大小写有区分。 二、特殊字符含义 文件名以“.”开头的都是隐藏文件/目录，只需在文件/目录名前加“.”就可隐藏它。 ~/ 表示主目录。 ./ 当前目录(一个点)。 ../ 上一级目录(两个点)。 ; 多个命令一起用。 > >> 输出重定向 。将一个命令的输出内容写入到一个文件里面。如果该文件存在， 就将该文件的内容覆盖； 如果不存在就先创建该文件， 然后再写入内容。 输出重定向，意思就是说，将原来屏幕输出变为文件输出，即将内容输到文件中。 < << 输入重定向。 本来命令是通过键盘得到输入的，但是用小于号，就能够使命令从文件中得到输入。 \ 表示未写完，回车换行再继续。 * 匹配零个或者多个字符。 ? 匹配一个字符。 [] 匹配中括号里的内容[a-z][A-Z][0-9]。 ！ 事件。 $ 取环境变量的值。 | 管道。把前一命令的输出作为后一命令的输入，把几个命令连接起来。 ｜经常跟tee连用，tee 把内容保存到文档并显示出来。 三、通用后接命令符 -a 所有(all)。 -e 所有(every)，比a更详细。 -f 取消保护。 -i 添加提示。 -p 强制执行。 -r 目录管理。 分屏显示的中途操作 空格<space> 继续打开下一屏； 回车<return> 继续打开下一行； b 另外开上一屏； f 另外开下一屏； h 帮助； q或Ctrl+C 退出； /字符串 从上往下查找匹配的字符串； ？字符串 从下往上查找匹配的字符串； n 继续查找。 四、退出命令 exit 退出; DOS内部命令 用于退出当前的命令处理器(COMMAND.COM) 恢复前一个命令处理器。 Ctrl+d 跟exit一样效果，表中止本次操作。 logout 当csh时可用来退出，其他shell不可用。 clear 清屏，清除(之前的内容并未删除，只是没看到，拉回上面可以看回)。 五、目录管理命令 pwd 显示当前所在目录，打印当前目录的绝对路径。 cd 进入某目录，DOS内部命令 显示或改变当前目录。 cd回车/cd ~ 都是回到自己的主目录。 cd . 当前目录(空格再加一个点)。 cd .. 回到上一级目录(空格再加两个点)。 cd ../.. 向上两级。 cd /user/s0807 从绝对路径去到某目录。 cd ~/s0807 直接进入主目录下的某目录(“cd ~"相当于主目录的路径的简写)。 ls 显示当前目录的所有目录和文件。 用法 ls [-aAbcCdeEfFghHilLmnopqrRstux1@] [file...] ls /etc/ 显示某目录下的所有文件和目录，如etc目录下的。 ls -l (list)列表显示文件(默认按文件名排序)， 显示文件的权限、硬链接数(即包含文件数,普通文件是1，目录1+)、用户、组名、大小、修改日期、文件名。 ls -t (time)按修改时间排序，显示目录和文件。 ls -lt 是“-l”和“-t”的组合，按时间顺序显示列表。 ls -F 显示文件类型，目录“/ ”结尾；可执行文件“*”结尾；文本文件(none)，没有结尾。 ls -R 递归显示目录结构。即该目录下的文件和各个副目录下的文件都一一显示。 ls -a 显示所有文件，包括隐藏文件。 文件权限 r 读权限。对普通文件来说，是读取该文件的权限；对目录来说，是获得该目录下的文件信息。 w 写权限。对文件，是修改；对目录，是增删文件与子目录。 (注 删除没有写权限的文件可以用 rm -f ，这是为了操作方便，是人性化的设计)。 x 执行权限；对目录，是进入该目录 - 表示没有权限 形式 - rw- r-- r-- 其中 第一个是文件类型(-表普通文件，d表目录，l表软链接文件) 第2~4个是属主，生成文件时登录的人，权限最高，用u表示 第5~7个是属组，系统管理员分配的同组的一个或几个人，用g表示 第8~10个是其他人，除属组外的人，用o表示 所有人，包括属主、属组及其他人，用a表示 chmod 更改权限； 用法 chmod [-fR] <绝对模式> 文件 ... chmod [-fR] <符号模式列表> 文件 ... 其中 <符号模式列表> 是一个用逗号分隔的表 [ugoa]{+|-|=}[rwxXlstugo] chmod u+rw 给用户加权限。同理，u-rw也可以减权限。 chmod u=rw 给用户赋权限。与加权限不一样，赋权限有覆盖的效果。 主要形式有如下几种 chmod u+rw chmod u=rw chmod u+r, u+w chmod u+rw,g+w, o+r chmod 777( 用数字的方式设置权限是最常用的) 数字表示权限时，各数位分别表示属主、属组及其他人； 其中，1是执行权(Execute)，2是写权限(Write)，4是读权限(Read)， 具体权限相当于三种权限的数相加，如7＝1+2+4，即拥有读写和执行权。 另外,临时文件/目录的权限为rwt，可写却不可删,关机后自动删除；建临时目录:chmod 777 目录名，再chmod +t 目录名。 id 显示用户有效的uid(用户字)和gid(组名) 用法 id [-ap] [user] id 显示自己的。 id root 显示root的。 id -a root 显示用户所在组的所有组名(如root用户，是所有组的组员) df 查看文件系统，查看数据区 用法 df [-F FSType] [-abeghklntVvZ] [-o FSType 特定选项] [目录 | 块设备 | 资源] df -k 以kbytes显示文件大小的查看文件系统方式 六、显示文件内容 more 分屏显示文件的内容。 用法 more [-cdflrsuw] [-行] [+行号] [+/模式] [文件名 ...]。 显示7个信息:用户名 密码 用户id(uid) 组id(gid) 描述信息(一般为空) 用户主目录 login shell(登录shell) cat 显示文件内容，不分屏(一般用在小文件，大文件显示不下)；合并文件，仅在屏幕上合并，并不改变原文件。 用法 cat [ -usvtebn ] [-|文件] ... tail 实时监控文件，一般用在日志文件，可以只看其中的几行。 用法 tail [+/-[n][lbc][f]] [文件] tail [+/-[n][l][r|f]] [文件] 七、文件/目录的增删 echo 显示一行内容。 touch 如果文件/目录不存在，则创建新文件/目录；如果文件存在，那么就是更新该文件的最后访问时间， 用法 touch [-acm] [-r ref_file] 文件... touch [-acm] [MMDDhhmm[yy]] 文件... touch [-acm] [-t [[CC]YY]MMDDhhmm[.SS]] file... mkdir 创建目录(必须有创建目录的权限) 用法 mkdir [-m 模式] [-p] dirname ... mkdir dir1/dir2 在dir1下建dir2 mkdir dir13 dir4 dir5 连建多个 mkdir ~/games 用户主目录下建(默认在当前目录下创建) mkdir -p dir6/dir7/dir8 强制创建dir8；若没有前面的目录，会自动创建dir6和dir7。 不用-p时，若没有dir6/dir7，则创建失败。 cp 复制文件/目录 cp 源文件 目标文件 复制文件；若已有文件则覆盖 cp -r 源目录 目标目录 复制目录；若已有目录则把源目录复制到目标目录下， 没有目标目录时，相当于完全复制源目录，只是文件名不同。 cp beans apple dir2 把beans、apple文件复制到dir2目录下 cp -i beans apple 增加是否覆盖的提示 mv 移动或重命名文件/目录 用法 mv [-f] [-i] f1 f2 mv [-f] [-i] f1 ... fn d1 mv [-f] [-i] d1 d2 mv 源文件名 目标文件名 若目标文件名还没有,则是源文件重命名为目标文件；若目标文件已存在，则源文件覆盖目标文件。 mv 源文件名 目标目录 移动文件 mv 源目录 目标目录 若目标目录不存在，则源目录重命名；若目标目录已存在，则源目录移动到目标目录下。 rm 删除文件/目录 用法 rm [-fiRr] 文件 ... rm 文件名 删除文件。 rm -r 目录名 删除目录。 rm –f 文件 只要是该文件或者目录的拥有者,无论是否有权限删除,都可以用这个命令参数强行删除。 rm -rf * 删除所有文件及目录 rmdir 删除空目录。只可以删除空目录。 ln 创建硬链接或软链接，硬链接＝同一文件的多个名字；软链接＝快捷方式 用法 ln [-f] [-n] [-s] f1 [f2] ln [-f] [-n] [-s] f1 ... fn d1 ln [-f] [-n] -s d1 d2 ln file1 file1.ln 创建硬链接。感觉是同一文件，删除一个，对另一个没有影响；须两个都删除才算删除。 ln -s file1 file1.sln 创建软链接。可跨系统操作，冲破操作权限；也是快捷方式。 八、时间显示 date 显示时间，精确到秒 用法 date [-u] mmddHHMM[[cc]yy][.SS] date [-u] [+format] date -a [-]sss[.fff] cal 显示日历 cal 9 2008 显示2008年9月的日历； cal 显示当月的 用法 cal [ [月] 年 ] 九、帮助 man 帮助( format and display the on-line manual pages) 用法 man [-] [-adFlrt] [-M 路径] [-T 宏软件包] [-s 段] 名称 ... man [-] [-adFlrt] [-M path] [-T macro-package] [-s section] name... man [-M 路径] -k 关键字 ... man [-M 路径] -f 文件 ... awk 按一定格式输出(pattern scanning and processing language) 用法 awk [-Fc] [-f 源代码 | 'cmds'] [文件] 十、vi 底行模式 ／？ 命令模式 i a o 输入模式 vi 的使用方法 1、光标 h 左 j 下 k 上 l 右 set nu 显示行号(set nonu) 21 光标停在指定行 21G 第N行 (G到文件尾，1G到文件头) 如果要将光标移动到文件第一行，那么就按 1G H 屏幕头 M 屏幕中间 L 屏幕底 ^ 或 shift+6 行首 $ 或 shift+4 行尾 Ctrl+f 下翻 Ctrl+b 上翻 2、输入 (输入模式) o 光标往下换一行 O (大写字母o)在光标所在行上插入一空行 i 在光标所在位置的前面插入字母 a 在光标所在位置的后面插入一个新字母 <Esc> 退出插入状态。 3、修改替换 r 替换一个字符 dd 删除行，剪切行 (5dd删除5行) 5,10d 删除 5 至 10 行(包括第 5行和第 10 行) x 删除一个字符 dw 删除词，剪切词。 ( 3dw删除 3 单词) cw 替换一个单词。 (cw 和 dw 的区别 cw 删除某一个单词后直接进入编辑模式，而dw删除词后仍处于命令模式) cc 替换一行 C 替换从光标到行尾 yy 复制行 (用法同下的 Y ，见下行) Y 将光标移动到要复制行位置，按yy。当你想粘贴的时候，请将光标移动到你想复制的位置的前一个位置，然后按 p yw 复制词 p 当前行下粘贴 1,2co3 复制行1，2在行3之后 4,5m6 移动行4，5在行6之后 u 当你的前一个命令操作是一个误操作的时候，那么可以按一下 u键，即可复原。只能撤销一次 r file2 在光标所在处插入另一个文件 ~ 将字母变成大写 J 可以将当前行与下一行连接起来 /字符串 从上往下找匹配的字符串 ?字符串 从下往上找匹配的字符串 n 继续查找 1,$s/旧串/新串/g 替换全文(或者 %s/旧串/新串/g) (1表示从第一行开始) 没有g则只替换一次，加g替换所有 3、存盘和退出 w 存盘 w newfile 存成新文件 wq 存盘再退出VI(或者ZZ或 X) q! 强行退出不存盘 查看用户 users 显示在线用户(仅显示用户名)。 who 显示在线用户，但比users更详细，包括用户名、终端号、登录时间、IP地址。 who am i 仅显示自己，(但包括用户名、端口、登录时间、IP地址；信息量＝who)。 whoami 也仅显示自己，但只有用户名(仅显示自己的有效的用户名)。 w 显示比who更多内容，还包括闲置时间、占CPU、平均占用CPU、执行命令。 用法 w [ -hlsuw ] [ 用户 ] su 改变用户，需再输入密码。 用法 su [-] [ username [ arg ... ] ] su － 相当于退出再重新登录。 查找 find 查找文件 用法 find [-H | -L] 路径列表 谓词列表 find / -name perl 从根目录开始查找名为perl的文件。 find . -mtime 10 -print 从当前目录查找距离现在10天时修改的文件，显示在屏幕上。 (注 “10”表示第10天的时候；如果是“+10”表示10天以外的范围；“-10”表示10天以内的范围。) grep 文件中查找字符；有过滤功能，只列出想要的内容 用法 grep -hblcnsviw 模式 文件 . . . 如 grep abc /etc/passwd 在passwd文件下找abc字符 wc 统计 -l 统计行数； -w统计单词数； -c 统计字符数 如 grep wang /etc/passwd|wc -l 统计passwd文件含“wang”的行数 du 查看目录情况 如 du -sk * 不加-s会显示子目录，-k按千字节排序 用法 du [-a] [-d] [-h|-k] [-r] [-o|-s] [-H|-L] [文件...] 进程管理 ps 显示进程。 用法 ps [ -aAdeflcjLPyZ ] [ -o 格式 ] [ -t 项列表 ] [ -u 用户列表 ] [ -U 用户列表 ] [ -G 组列表 ] [ -p 进程列表 ] [ -g 程序组列表 ] [ -s 标识符列表 ] [ -z 区域列表 ] ps 显示自己的进程。 ps －e 显示每个进程，包括空闲进程。 ps －f 显示详情。 ps －ef 组合－e和－f，所有进程的详情。 ps －U uidlist(用户列表) 具体查看某人的进程。 kill pkill sleep jobs 用法 jobs [-l ] fg ％n bg ％n stop ％n 挂起(仅csh能用) Ctrl+C Ctrl+Z 网络链接 ping usage ping host [timeout] usage ping -s [-l | U] [adLnRrv] [-A addr_family] [-c traffic_class] [-g gateway [-g gateway ...]] [-F flow_label] [-I interval] [-i interface] [-P tos] [-p port] [-t ttl] host [data_size] [npackets] ifconfig －a /sbin/ifconfig 查看本机的IP地址 netstat －rn rlogin ftp 帮助文件 [sd0807@localhost ~]$ help GNU bash, version 3.1.17(1)-release (i686-redhat-linux-gnu) These shell commands are defined internally. Type `help' to see this list. Type `help name' to find out more about the function `name'. Use `info bash' to find out more about the shell in general. Use `man -k' or `info' to find out more about commands not in this list. A star (*) next to a name means that the command is disabled. JOB_SPEC [&] (( expression )) . filename [arguments] [ arg... ] [[ expression ]] alias [-p] [name[=value] ... ] bg [job_spec ...] bind [-lpvsPVS] [-m keymap] [-f fi break [n] builtin [shell-builtin [arg ...]] caller [EXPR] case WORD in [PATTERN [| PATTERN]. cd [-L|-P] [dir] command [-pVv] command [arg ...] compgen [-abcdefgjksuv] [-o option complete [-abcdefgjksuv] [-pr] [-o continue [n] declare [-afFirtx] [-p] [name[=val dirs [-clpv] [+N] [-N] disown [-h] [-ar] [jobspec ...] echo [-neE] [arg ...] enable [-pnds] [-a] [-f filename] eval [arg ...] exec [-cl] [-a name] file [redirec exit [n] export [-nf] [name[=value] ...] or false fc [-e ename] [-nlr] [first] [last fg [job_spec] for NAME [in WORDS ... ;] do COMMA for (( exp1; exp2; exp3 )); do COM function NAME { COMMANDS ; } or NA getopts optstring name [arg] hash [-lr] [-p pathname] [-dt] [na help [-s] [pattern ...] history [-c] [-d offset] [n] or hi if COMMANDS; then COMMANDS; [ elif jobs [-lnprs] [jobspec ...] or job kill [-s sigspec | -n signum | -si let arg [arg ...] local name[=value] ... logout popd [+N | -N] [-n] printf [-v var] format [arguments] pushd [dir | +N | -N] [-n] pwd [-LP] read [-ers] [-u fd] [-t timeout] [ readonly [-af] [name[=value] ...] return [n] select NAME [in WORDS ... ;] do CO set [--abefhkmnptuvxBCHP] [-o option] [arg ...] shift [n] shopt [-pqsu] [-o long-option] opt source filename [arguments] suspend [-f] test [expr] time [-p] PIPELINE times trap [-lp] [arg signal_spec ...] true type [-afptP] name [name ...] typeset [-afFirtx] [-p] name[=valu ulimit [-SHacdfilmnpqstuvx] [limit umask [-p] [-S] [mode] unalias [-a] name [name ...] unset [-f] [-v] [name ...] until COMMANDS; do COMMANDS; done variables - Some variable names an wait [n] while COMMANDS; do COMMANDS; done { COMMANDS ; } 输入 man help BASH_BUILTINS(1) BASH_BUILTINS(1) NAME bash, :, ., [, alias, bg, bind, break, builtin, cd, command, compgen, complete, continue, declare, dirs, disown, echo, enable, eval, exec, exit, export, fc, fg, getopts, hash, help, history, jobs, kill, let, local, logout, popd, printf, pushd, pwd, read, readonly, return, set, shift, shopt, source, suspend, test, times, trap, type, typeset, ulimit, umask, una- lias, unset, wait - bash built-in commands, see bash(1) BASH BUILTIN COMMANDS Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts -- to signify the end of the options. For example, the :, true, false, and test builtins do not accept options. : [arguments] No effect; the command does nothing beyond expanding arguments and performing any specified redirections. A zero exit code is returned. . filename [arguments] source filename [arguments] Read and execute commands from filename in the current shell environment and return the exit status of the last command executed from filename. If filename does not contain a slash, file names in PATH are used to find the directory containing file- name. The file searched for in PATH need not be executable. When bash is not in posix mode, the current directory is searched if no file is found in PATH. If the sourcepath option to the shopt builtin command is turned off, the PATH is not searched. If any arguments are supplied, they become the positional parameters when filename is executed. Otherwise the positional parameters are unchanged. The return status is the status of the last command exited within the script (0 if no commands are executed), and false if filename is not found or cannot be read. alias [-p] [name[=value] ...] Alias with no arguments or with the -p option prints the list of aliases in the form alias name=value on standard output. When arguments are supplied, an alias is defined for each name whose value is given. A trailing space in value causes the next word to be checked for alias substitution when the alias is expanded. For each name in the argument list for which no value is supplied, the name and value of the alias is printed. Alias returns true unless a name is given for which no alias has been defined. bg [jobspec ...] Resume each suspended job jobspec in the background, as if it had been started with &. If jobspec is not present, the shell’s notion of the current job is used. bg jobspec returns 0 unless run when job control is disabled or, when run with job con- trol enabled, any specified jobspec was not found or was started without job control. bind [-m keymap] [-lpsvPSV] bind [-m keymap] [-q function] [-u function] [-r keyseq] bind [-m keymap] -f filename bind [-m keymap] -x keyseq:shell-command bind [-m keymap] keyseq:function-name bind readline-command Display current readline key and function bindings, bind a key sequence to a readline function or macro, or set a readline variable. Each non-option argument is a command as it would appear in .inputrc, but each binding or command must be passed as a sepa- rate argument; e.g., ’"\C-x\C-r": re-read-init-file’. Options, if supplied, have the following meanings: -m keymap Use keymap as the keymap to be affected by the subsequent bindings. Accept- able keymap names are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert. vi is equivalent to vi-command; emacs is equivalent to emacs-standard. -l List the names of all readline functions. -p Display readline function names and bindings in such a way that they can be re-read. -P List current readline function names and bindings. -v Display readline variable names and values in such a way that they can be re- read. -V List current readline variable names and values. -s Display readline key sequences bound to macros and the strings they output in such a way that they can be re-read. -S Display readline key sequences bound to macros and the strings they output. -f filename Read key bindings from filename. -q function Query about which keys invoke the named function. -u function Unbind all keys bound to the named function. -r keyseq Remove any current binding for keyseq. -x keyseq:shell-command Cause shell-command to be executed whenever keyseq is entered. The return value is 0 unless an unrecognized option is given or an error occurred. break [n] Exit from within a for, while, until, or select loop. If n is specified, break n levels. n must be ≥ 1. If n is greater than the number of enclosing loops, all enclosing loops are exited. The return value is 0 unless the shell is not executing a loop when break is executed. builtin shell-builtin [arguments] Execute the specified shell builtin, passing it arguments, and return its exit sta- tus. This is useful when defining a function whose name is the same as a shell builtin, retaining the functionality of the builtin within the function. The cd builtin is commonly redefined this way. The return status is false if shell-builtin is not a shell builtin command. cd [-L|-P] [dir] Change the current directory to dir. The variable HOME is the default dir. The variable CDPATH defines the search path for the directory containing dir. Alterna- tive directory names in CDPATH are separated by a colon (:). A null directory name in CDPATH is the same as the current directory, i.e., ‘‘.’’. If dir begins with a slash (/), then CDPATH is not used. The -P option says to use the physical directory structure instead of following symbolic links (see also the -P option to the set builtin command); the -L option forces symbolic links to be followed. An argument of - is equivalent to $OLDPWD. If a non-empty directory name from CDPATH is used, or if - is the first argument, and the directory change is successful, the absolute path- name of the new working directory is written to the standard output. The return value is true if the directory was successfully changed; false otherwise. caller [expr] Returns the context of any active subroutine call (a shell function or a script exe- cuted with the . or source builtins. Without expr, caller displays the line number and source filename of the current subroutine call. If a non-negative integer is supplied as expr, caller displays the line number, subroutine name, and source file corresponding to that position in the current execution call stack. This extra information may be used, for example, to print a stack trace. The current frame is frame 0. The return value is 0 unless the shell is not executing a subroutine call or expr does not correspond to a valid position in the call stack. command [-pVv] command [arg ...] Run command with args suppressing the normal shell function lookup. Only builtin com- mands or commands found in the PATH are executed. If the -p option is given, the search for command is performed using a default value for PATH that is guaranteed to find all of the standard utilities. If either the -V or -v option is supplied, a description of command is printed. The -v option causes a single word indicating the command or file name used to invoke command to be displayed; the -V option produces a more verbose description. If the -V or -v option is supplied, the exit status is 0 if command was found, and 1 if not. If neither option is supplied and an error occurred or command cannot be found, the exit status is 127. Otherwise, the exit status of the command builtin is the exit status of command. compgen [option] [word] Generate possible completion matches for word according to the options, which may be any option accepted by the complete builtin with the exception of -p and -r, and write the matches to the standard output. When using the -F or -C options, the vari- ous shell variables set by the programmable completion facilities, while available, will not have useful values. The matches will be generated in the same way as if the programmable completion code had generated them directly from a completion specification with the same flags. If word is specified, only those completions matching word will be displayed. The return value is true unless an invalid option is supplied, or no matches were generated. complete [-abcdefgjksuv] [-o comp-option] [-A action] [-G globpat] [-W wordlist] [-P prefix] [-S suffix] [-X filterpat] [-F function] [-C command] name [name ...] complete -pr [name ...] Specify how arguments to each name should be completed. If the -p option is sup- plied, or if no options are supplied, existing completion specifications are printed in a way that allows them to be reused as input. The -r option removes a completion specification for each name, or, if no names are supplied, all completion specifica- tions. The process of applying these completion specifications when word completion is attempted is described above under Programmable Completion. Other options, if specified, have the following meanings. The arguments to the -G, -W, and -X options (and, if necessary, the -P and -S options) should be quoted to protect them from expansion before the complete builtin is invoked. -o comp-option The comp-option controls several aspects of the compspec’s behavior beyond the simple generation of completions. comp-option may be one of: bashdefault Perform the rest of the default bash completions if the compspec gen- erates no matches. default Use readline’s default filename completion if the compspec generates no matches. dirnames Perform directory name completion if the compspec generates no matches. filenames Tell readline that the compspec generates filenames, so it can per- form any filename-specific processing (like adding a slash to direc- tory names or suppressing trailing spaces). Intended to be used with shell functions. nospace Tell readline not to append a space (the default) to words completed at the end of the line. plusdirs After any matches defined by the compspec are generated, directory name completion is attempted and any matches are added to the results of the other actions. -A action The action may be one of the following to generate a list of possible comple- tions: alias Alias names. May also be specified as -a. arrayvar Array variable names. binding Readline key binding names. builtin Names of shell builtin commands. May also be specified as -b. command Command names. May also be specified as -c. directory Directory names. May also be specified as -d. disabled Names of disabled shell builtins. enabled Names of enabled shell builtins. export Names of exported shell variables. May also be specified as -e. file File names. May also be specified as -f. function Names of shell functions. group Group names. May also be specified as -g. helptopic Help topics as accepted by the help builtin. hostname Hostnames, as taken from the file specified by the HOSTFILE shell variable. job Job names, if job control is active. May also be specified as -j. keyword Shell reserved words. May also be specified as -k. running Names of running jobs, if job control is active. service Service names. May also be specified as -s. setopt Valid arguments for the -o option to the set builtin. shopt Shell option names as accepted by the shopt builtin. signal Signal names. stopped Names of stopped jobs, if job control is active. user User names. May also be specified as -u. variable Names of all shell variables. May also be specified as -v. -G globpat The filename expansion pattern globpat is expanded to generate the possible completions. -W wordlist The wordlist is split using the characters in the IFS special variable as delimiters, and each resultant word is expanded. The possible completions are the members of the resultant list which match the word being completed. -C command command is executed in a subshell environment, and its output is used as the possible completions. -F function The shell function function is executed in the current shell environment. When it finishes, the possible completions are retrieved from the value of the COMPREPLY array variable. -X filterpat filterpat is a pattern as used for filename expansion. It is applied to the list of possible completions generated by the preceding options and argu- ments, and each completion matching filterpat is removed from the list. A leading ! in filterpat negates the pattern; in this case, any completion not matching filterpat is removed. -P prefix prefix is added at the beginning of each possible completion after all other options have been applied. -S suffix suffix is appended to each possible completion after all other options have been applied. The return value is true unless an invalid option is supplied, an option other than -p or -r is supplied without a name argument, an attempt is made to remove a comple- tion specification for a name for which no specification exists, or an error occurs adding a completion specification. continue [n] Resume the next iteration of the enclosing for, while, until, or select loop. If n is specified, resume at the nth enclosing loop. n must be ≥ 1. If n is greater than the number of enclosing loops, the last enclosing loop (the ‘‘top-level’’ loop) is resumed. The return value is 0 unless the shell is not executing a loop when con- tinue is executed. declare [-afFirtx] [-p] [name[=value] ...] typeset [-afFirtx] [-p] [name[=value] ...] Declare variables and/or give them attributes. If no names are given then display the values of variables. The -p option will display the attributes and values of each name. When -p is used, additional options are ignored. The -F option inhibits the display of function definitions; only the function name and attributes are printed. If the extdebug shell option is enabled using shopt, the source file name and line number where the function is defined are displayed as well. The -F option implies -f. The following options can be used to restrict output to variables with the specified attribute or to give variables attributes: -a Each name is an array variable (see Arrays above). -f Use function names only. -i The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION ) is performed when the variable is assigned a value. -r Make names readonly. These names cannot then be assigned values by subsequent assignment statements or unset. -t Give each name the trace attribute. Traced functions inherit the DEBUG and RETURN traps from the calling shell. The trace attribute has no special mean- ing for variables. -x Mark names for export to subsequent commands via the environment. Using ‘+’ instead of ‘-’ turns off the attribute instead, with the exception that +a may not be used to destroy an array variable. When used in a function, makes each name local, as with the local command. If a variable name is followed by =value, the value of the variable is set to value. The return value is 0 unless an invalid option is encountered, an attempt is made to define a function using ‘‘-f foo=bar’’, an attempt is made to assign a value to a readonly variable, an attempt is made to assign a value to an array variable without using the compound assignment syntax (see Arrays above), one of the names is not a valid shell variable name, an attempt is made to turn off readonly status for a readonly variable, an attempt is made to turn off array status for an array variable, or an attempt is made to display a non-exis- tent function with -f. dirs [-clpv] [+n] [-n] Without options, displays the list of currently remembered directories. The default display is on a single line with directory names separated by spaces. Directories are added to the list with the pushd command; the popd command removes entries from the list. +n Displays the nth entry counting from the left of the list shown by dirs when invoked without options, starting with zero. -n Displays the nth entry counting from the right of the list shown by dirs when invoked without options, starting with zero. -c Clears the directory stack by deleting all of the entries. -l Produces a longer listing; the default listing format uses a tilde to denote the home directory. -p Print the directory stack with one entry per line. -v Print the directory stack with one entry per line, prefixing each entry with its index in the stack. The return value is 0 unless an invalid option is supplied or n indexes beyond the end of the directory stack. disown [-ar] [-h] [jobspec ...] Without options, each jobspec is removed from the table of active jobs. If the -h option is given, each jobspec is not removed from the table, but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. If no jobspec is present, and neither the -a nor the -r option is supplied, the current job is used. If no jobspec is supplied, the -a option means to remove or mark all jobs; the -r option without a jobspec argument restricts operation to running jobs. The return value is 0 unless a jobspec does not specify a valid job. echo [-neE] [arg ...] Output the args, separated by spaces, followed by a newline. The return status is always 0. If -n is specified, the trailing newline is suppressed. If the -e option is given, interpretation of the following backslash-escaped characters is enabled. The -E option disables the interpretation of these escape characters, even on systems where they are interpreted by default. The xpg_echo shell option may be used to dynamically determine whether or not echo expands these escape characters by default. echo does not interpret -- to mean the end of options. echo interprets the following escape sequences: \a alert (bell) \b backspace \c suppress trailing newline \e an escape character \f form feed \n new line \r carriage return \t horizontal tab \v vertical tab \\ backslash \0nnn the eight-bit character whose value is the octal value nnn (zero to three octal digits) \nnn the eight-bit character whose value is the octal value nnn (one to three octal digits) \xHH the eight-bit character whose value is the hexadecimal value HH (one or two hex digits) enable [-adnps] [-f filename] [name ...] Enable and disable builtin shell commands. Disabling a builtin allows a disk command which has the same name as a shell builtin to be executed without specifying a full pathname, even though the shell normally searches for builtins before disk commands. If -n is used, each name is disabled; otherwise, names are enabled. For example, to use the test binary found via the PATH instead of the shell builtin version, run ‘‘enable -n test’’. The -f option means to load the new builtin command name from shared object filename, on systems that support dynamic loading. The -d option will delete a builtin previously loaded with -f. If no name arguments are given, or if the -p option is supplied, a list of shell builtins is printed. With no other option arguments, the list consists of all enabled shell builtins. If -n is supplied, only disabled builtins are printed. If -a is supplied, the list printed includes all builtins, with an indication of whether or not each is enabled. If -s is supplied, the output is restricted to the POSIX special builtins. The return value is 0 unless a name is not a shell builtin or there is an error loading a new builtin from a shared object. eval [arg ...] The args are read and concatenated together into a single command. This command is then read and executed by the shell, and its exit status is returned as the value of eval. If there are no args, or only null arguments, eval returns 0. exec [-cl] [-a name] [command [arguments]] If command is specified, it replaces the shell. No new process is created. The arguments become the arguments to command. If the -l option is supplied, the shell places a dash at the beginning of the zeroth arg passed to command. This is what login(1) does. The -c option causes command to be executed with an empty environ- ment. If -a is supplied, the shell passes name as the zeroth argument to the exe- cuted command. If command cannot be executed for some reason, a non-interactive shell exits, unless the shell option execfail is enabled, in which case it returns failure. An interactive shell returns failure if the file cannot be executed. If command is not specified, any redirections take effect in the current shell, and the return status is 0. If there is a redirection error, the return status is 1. exit [n] Cause the shell to exit with a status of n. If n is omitted, the exit status is that of the last command executed. A trap on EXIT is executed before the shell termi- nates. export [-fn] [name[=word]] ... export -p The supplied names are marked for automatic export to the environment of subsequently executed commands. If the -f option is given, the names refer to functions. If no names are given, or if the -p option is supplied, a list of all names that are exported in this shell is printed. The -n option causes the export property to be removed from each name. If a variable name is followed by =word, the value of the variable is set to word. export returns an exit status of 0 unless an invalid option is encountered, one of the names is not a valid shell variable name, or -f is sup- plied with a name that is not a function. fc [-e ename] [-nlr] [first] [last] fc -s [pat=rep] [cmd] Fix Command. In the first form, a range of commands from first to last is selected from the history list. First and last may be specified as a string (to locate the last command beginning with that string) or as a number (an index into the history list, where a negative number is used as an offset from the current command number). If last is not specified it is set to the current command for listing (so that ‘‘fc -l -10’’ prints the last 10 commands) and to first otherwise. If first is not speci- fied it is set to the previous command for editing and -16 for listing. The -n option suppresses the command numbers when listing. The -r option reverses the order of the commands. If the -l option is given, the commands are listed on standard output. Otherwise, the editor given by ename is invoked on a file contain- ing those commands. If ename is not given, the value of the FCEDIT variable is used, and the value of EDITOR if FCEDIT is not set. If neither variable is set, is used. When editing is complete, the edited commands are echoed and executed. In the second form, command is re-executed after each instance of pat is replaced by rep. A useful alias to use with this is ‘‘r="fc -s"’’, so that typing ‘‘r cc’’ runs the last command beginning with ‘‘cc’’ and typing ‘‘r’’ re-executes the last command. If the first form is used, the return value is 0 unless an invalid option is encoun- tered or first or last specify history lines out of range. If the -e option is sup- plied, the return value is the value of the last command executed or failure if an error occurs with the temporary file of commands. If the second form is used, the return status is that of the command re-executed, unless cmd does not specify a valid history line, in which case fc returns failure. fg [jobspec] Resume jobspec in the foreground, and make it the current job. If jobspec is not present, the shell’s notion of the current job is used. The return value is that of the command placed into the foreground, or failure if run when job control is dis- abled or, when run with job control enabled, if jobspec does not specify a valid job or jobspec specifies a job that was started without job control. getopts optstring name [args] getopts is used by shell procedures to parse positional parameters. optstring con- tains the option characters to be recognized; if a character is followed by a colon, the option is expected to have an argument, which should be separated from it by white space. The colon and question mark characters may not be used as option char- acters. Each time it is invoked, getopts places the next option in the shell vari- able name, initializing name if it does not exist, and the index of the next argument to be processed into the variable OPTIND. OPTIND is initialized to 1 each time the shell or a shell script is invoked. When an option requires an argument, getopts places that argument into the variable OPTARG. The shell does not reset OPTIND auto- matically; it must be manually reset between multiple calls to getopts within the same shell invocation if a new set of parameters is to be used. When the end of options is encountered, getopts exits with a return value greater than zero. OPTIND is set to the index of the first non-option argument, and name is set to ?. getopts normally parses the positional parameters, but if more arguments are given in args, getopts parses those instead. getopts can report errors in two ways. If the first character of optstring is a colon, silent error reporting is used. In normal operation diagnostic messages are printed when invalid options or missing option arguments are encountered. If the variable OPTERR is set to 0, no error messages will be displayed, even if the first character of optstring is not a colon. If an invalid option is seen, getopts places ? into name and, if not silent, prints an error message and unsets OPTARG. If getopts is silent, the option character found is placed in OPTARG and no diagnostic message is printed. If a required argument is not found, and getopts is not silent, a question mark (?) is placed in name, OPTARG is unset, and a diagnostic message is printed. If getopts is silent, then a colon (:) is placed in name and OPTARG is set to the option charac- ter found. getopts returns true if an option, specified or unspecified, is found. It returns false if the end of options is encountered or an error occurs. hash [-lr] [-p filename] [-dt] [name] For each name, the full file name of the command is determined by searching the directories in $PATH and remembered. If the -p option is supplied, no path search is performed, and filename is used as the full file name of the command. The -r option causes the shell to forget all remembered locations. The -d option causes the shell to forget the remembered location of each name. If the -t option is supplied, the full pathname to which each name corresponds is printed. If multiple name arguments are supplied with -t, the name is printed before the hashed full pathname. The -l option causes output to be displayed in a format that may be reused as input. If no arguments are given, or if only -l is supplied, information about remembered commands is printed. The return status is true unless a name is not found or an invalid option is supplied. help [-s] [pattern] Display helpful information about builtin commands. If pattern is specified, help gives detailed help on all commands matching pattern; otherwise help for all the builtins and shell control structures is printed. The -s option restricts the infor- mation displayed to a short usage synopsis. The return status is 0 unless no command matches pattern. history [n] history -c history -d offset history -anrw [filename] history -p arg [arg ...] history -s arg [arg ...] With no options, display the command history list with line numbers. Lines listed with a * have been modified. An argument of n lists only the last n lines. If the shell variable HISTTIMEFORMAT is set and not null, it is used as a format string for strftime(3) to display the time stamp associated with each displayed history entry. No intervening blank is printed between the formatted time stamp and the history line. If filename is supplied, it is used as the name of the history file; if not, the value of HISTFILE is used. Options, if supplied, have the following meanings: -c Clear the history list by deleting all the entries. -d offset Delete the history entry at position offset. -a Append the ‘‘new’’ history lines (history lines entered since the beginning of the current bash session) to the history file. -n Read the history lines not already read from the history file into the current history list. These are lines appended to the history file since the begin- ning of the current bash session. -r Read the contents of the history file and use them as the current history. -w Write the current history to the history file, overwriting the history file’s contents. -p Perform history substitution on the following args and display the result on the standard output. Does not store the results in the history list. Each arg must be quoted to disable normal history expansion. -s Store the args in the history list as a single entry. The last command in the history list is removed before the args are added. If the HISTTIMEFORMAT is set, the time stamp information associated with each history entry is written to the history file. The return value is 0 unless an invalid option is encountered, an error occurs while reading or writing the history file, an invalid offset is supplied as an argument to -d, or the history expansion supplied as an argument to -p fails. jobs [-lnprs] [ jobspec ... ] jobs -x command [ args ... ] The first form lists the active jobs. The options have the following meanings: -l List process IDs in addition to the normal information. -p List only the process ID of the job’s process group leader. -n Display information only about jobs that have changed status since the user was last notified of their status. -r Restrict output to running jobs. -s Restrict output to stopped jobs. If jobspec is given, output is restricted to information about that job. The return status is 0 unless an invalid option is encountered or an invalid jobspec is sup- plied. If the -x option is supplied, jobs replaces any jobspec found in command or args with the corresponding process group ID, and executes command passing it args, returning its exit status. kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ... kill -l [sigspec | exit_status] Send the signal named by sigspec or signum to the processes named by pid or jobspec. sigspec is either a case-insensitive signal name such as SIGKILL (with or without the SIG prefix) or a signal number; signum is a signal number. If sigspec is not present, then SIGTERM is assumed. An argument of -l lists the signal names. If any arguments are supplied when -l is given, the names of the signals corresponding to the arguments are listed, and the return status is 0. The exit_status argument to -l is a number specifying either a signal number or the exit status of a process termi- nated by a signal. kill returns true if at least one signal was successfully sent, or false if an error occurs or an invalid option is encountered. let arg [arg ...] Each arg is an arithmetic expression to be evaluated (see ARITHMETIC EVALUATION). If the last arg evaluates to 0, let returns 1; 0 is returned otherwise. local [option] [name[=value] ...] For each argument, a local variable named name is created, and assigned value. The option can be any of the options accepted by declare. When local is used within a function, it causes the variable name to have a visible scope restricted to that function and its children. With no operands, local writes a list of local variables to the standard output. It is an error to use local when not within a function. The return status is 0 unless local is used outside a function, an invalid name is sup- plied, or name is a readonly variable. logout Exit a login shell. popd [-n] [+n] [-n] Removes entries from the directory stack. With no arguments, removes the top direc- tory from the stack, and performs a cd to the new top directory. Arguments, if sup- plied, have the following meanings: +n Removes the nth entry counting from the left of the list shown by dirs, start- ing with zero. For example: ‘‘popd +0’’ removes the first directory, ‘‘popd +1’’ the second. -n Removes the nth entry counting from the right of the list shown by dirs, starting with zero. For example: ‘‘popd -0’’ removes the last directory, ‘‘popd -1’’ the next to last. -n Suppresses the normal change of directory when removing directories from the stack, so that only the stack is manipulated. If the popd command is successful, a dirs is performed as well, and the return status is 0. popd returns false if an invalid option is encountered, the directory stack is empty, a non-existent directory stack entry is specified, or the directory change fails. printf [-v var] format [arguments] Write the formatted arguments to the standard output under the control of the format. The format is a character string which contains three types of objects: plain charac- ters, which are simply copied to standard output, character escape sequences, which are converted and copied to the standard output, and format specifications, each of which causes printing of the next successive argument. In addition to the standard printf(1) formats, %b causes printf to expand backslash escape sequences in the cor- responding argument (except that \c terminates output, backslashes in \', \", and \? are not removed, and octal escapes beginning with \0 may contain up to four digits), and %q causes printf to output the corresponding argument in a format that can be reused as shell input. The -v option causes the output to be assigned to the variable var rather than being printed to the standard output. The format is reused as necessary to consume all of the arguments. If the format requires more arguments than are supplied, the extra format specifications behave as if a zero value or null string, as appropriate, had been supplied. The return value is zero on success, non-zero on failure. pushd [-n] [dir] pushd [-n] [+n] [-n] Adds a directory to the top of the directory stack, or rotates the stack, making the new top of the stack the current working directory. With no arguments, exchanges the top two directories and returns 0, unless the directory stack is empty. Arguments, if supplied, have the following meanings: +n Rotates the stack so that the nth directory (counting from the left of the list shown by dirs, starting with zero) is at the top. -n Rotates the stack so that the nth directory (counting from the right of the list shown by dirs, starting with zero) is at the top. -n Suppresses the normal change of directory when adding directories to the stack, so that only the stack is manipulated. dir Adds dir to the directory stack at the top, making it the new current working directory. If the pushd command is successful, a dirs is performed as well. If the first form is used, pushd returns 0 unless the cd to dir fails. With the second form, pushd returns 0 unless the directory stack is empty, a non-existent directory stack element is specified, or the directory change to the specified new current directory fails. pwd [-LP] Print the absolute pathname of the current working directory. The pathname printed contains no symbolic links if the -P option is supplied or the -o physical option to the set builtin command is enabled. If the -L option is used, the pathname printed may contain symbolic links. The return status is 0 unless an error occurs while reading the name of the current directory or an invalid option is supplied. read [-ers] [-u fd] [-t timeout] [-a aname] [-p prompt] [-n nchars] [-d delim] [name ...] One line is read from the standard input, or from the file descriptor fd supplied as an argument to the -u option, and the first word is assigned to the first name, the second word to the second name, and so on, with leftover words and their intervening separators assigned to the last name. If there are fewer words read from the input stream than names, the remaining names are assigned empty values. The characters in IFS are used to split the line into words. The backslash character (\) may be used to remove any special meaning for the next character read and for line continuation. Options, if supplied, have the following meanings: -a aname The words are assigned to sequential indices of the array variable aname, starting at 0. aname is unset before any new values are assigned. Other name arguments are ignored. -d delim The first character of delim is used to terminate the input line, rather than newline. -e If the standard input is coming from a terminal, readline (see READLINE above) is used to obtain the line. -n nchars read returns after reading nchars characters rather than waiting for a com- plete line of input. -p prompt Display prompt on standard error, without a trailing newline, before attempt- ing to read any input. The prompt is displayed only if input is coming from a terminal. -r Backslash does not act as an escape character. The backslash is considered to be part of the line. In particular, a backslash-newline pair may not be used as a line continuation. -s Silent mode. If input is coming from a terminal, characters are not echoed. -t timeout Cause read to time out and return failure if a complete line of input is not read within timeout seconds. This option has no effect if read is not reading input from the terminal or a pipe. -u fd Read input from file descriptor fd. If no names are supplied, the line read is assigned to the variable REPLY. The return code is zero, unless end-of-file is encountered, read times out, or an invalid file descriptor is supplied as the argument to -u. readonly [-apf] [name[=word] ...] The given names are marked readonly; the values of these names may not be changed by subsequent assignment. If the -f option is supplied, the functions corresponding to the names are so marked. The -a option restricts the variables to arrays. If no name arguments are given, or if the -p option is supplied, a list of all readonly names is printed. The -p option causes output to be displayed in a format that may be reused as input. If a variable name is followed by =word, the value of the vari- able is set to word. The return status is 0 unless an invalid option is encountered, one of the names is not a valid shell variable name, or -f is supplied with a name that is not a function. return [n] Causes a function to exit with the return value specified by n. If n is omitted, the return status is that of the last command executed in the function body. If used outside a function, but during execution of a script by the . (source) command, it causes the shell to stop executing that script and return either n or the exit status of the last command executed within the script as the exit status of the script. If used outside a function and not during execution of a script by ., the return status is false. Any command associated with the RETURN trap is executed before execution resumes after the function or script. set [--abefhkmnptuvxBCHP] [-o option] [arg ...] Without options, the name and value of each shell variable are displayed in a format that can be reused as input for setting or resetting the currently-set variables. Read-only variables cannot be reset. In posix mode, only shell variables are listed. The output is sorted according to the current locale. When options are specified, they set or unset shell attributes. Any arguments remaining after the options are processed are treated as values for the positional parameters and are assigned, in order, to $1, $2, ... $n. Options, if specified, have the following meanings: -a Automatically mark variables and functions which are modified or created for export to the environment of subsequent commands. -b Report the status of terminated background jobs immediately, rather than before the next primary prompt. This is effective only when job control is enabled. -e Exit immediately if a simple command (see SHELL GRAMMAR above) exits with a non-zero status. The shell does not exit if the command that fails is part of the command list immediately following a while or until keyword, part of the test in an if statement, part of a && or ││ list, or if the command’s return value is being inverted via !. A trap on ERR, if set, is executed before the shell exits. -f Disable pathname expansion. -h Remember the location of commands as they are looked up for execution. This is enabled by default. -k All arguments in the form of assignment statements are placed in the environ- ment for a command, not just those that precede the command name. -m Monitor mode. Job control is enabled. This option is on by default for interactive shells on systems that support it (see JOB CONTROL above). Back- ground processes run in a separate process group and a line containing their exit status is printed upon their completion. -n Read commands but do not execute them. This may be used to check a shell script for syntax errors. This is ignored by interactive shells. -o option-name The option-name can be one of the following: allexport Same as -a. braceexpand Same as -B. emacs Use an emacs-style command line editing interface. This is enabled by default when the shell is interactive, unless the shell is started with the --noediting option. errtrace Same as -E. functrace Same as -T. errexit Same as -e. hashall Same as -h. histexpand Same as -H. history Enable command history, as described above under HISTORY. This option is on by default in interactive shells. ignoreeof The effect is as if the shell command ‘‘IGNOREEOF=10’’ had been exe- cuted (see Shell Variables above). keyword Same as -k. monitor Same as -m. noclobber Same as -C. noexec Same as -n. noglob Same as -f. nolog Currently ignored. notify Same as -b. nounset Same as -u. onecmd Same as -t. physical Same as -P. pipefail If set, the return value of a pipeline is the value of the last (rightmost) command to exit with a non-zero status, or zero if all command
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