[SOLVED] CS you should know the following shell concepts

you should know the following shell concepts
hierarchical file system
directory tree
root directory

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home directory
standard directory contents
/etc: configuration files
/dev: device files
/home: user home directories
/lib: shared library files used by core systems programs
/sbin: system binaries for vital system tasks
/usr: programs and support files for users
/var: system log files
absolute path: starts with root directory, that is /, and specifies a
complete path for a file or a directory, e.g. /usr/bin/firefox
relative path: specifies the path for a file relative to the current
directory; e.g. if the current directory is /usr, then ./bin/firefox is a
relative path for the firefox binary
types of shell commands
binary files: separate programs executed by shell
shell builtins: commands interpreted by shell, the functionality for these
commands are implemented in the shell program itself
aliases: shortcuts defined by users to avoid typing of long commands or
command sequences
shell variables: variables that a user can set to control shells behavior
PATH: when a user types a command, shell looks for the binary in the list
of directories present in the PATH variable.
input/output redirection
every program executed in shell has three streams associated with it
standard input: where the program reads the input from; attached to
keyboard by default
standard output: where the program writes its output; attached to screen
by default
standard error: where the program writes its errors; attached to screen
by default
shell allows us to redirect these streams from their defaults
use > to redirect standard output to a file:
ls -l /usr/bin >ls-output.txt
use >> to append standard output to a file; using >> will append to a
file whereas using > will wipe the output of the file first before
writing to it; thus, after the following commands, the file ls-output.txt
will have twice the contents of the /usr/bin directory:
ls -l /usr/bin >ls-output.txt
ls -l /usr/bin >>ls-output.txt
use 2> to redirect standard error to a file:
ls -l /nonexistentfile 2>ls-error.txt
use < to read input from a file instead of keyboard:- cat < /etc/passwd- shell allows us to send the output of one program to the input of anotherprogram using pipe (|). the following command sequence sends the output of”ls -l /usr/bin” command to the input of “less” command for easier- ls -l /usr/bin | less- shell allows us to form powerful pipelines to perform arbitrarily complextasks. see the lecture for an example.- you should know the following shell commands; use tldr command to find out themost frequently used forms of these commands:- the following is an example shell session. you should be able to understandand explain what is going on:demo DocumentsMusic Templates VideosDesktopDownloadsPublictypescriptbindev liblibx32mnt rootsnapsysvarboot etc lib32lost+foundopt run srv tmpcdromhomelib64media procsbinswapfileusr..config.gitconfigPublic typescript.. demo .gnupg.ssh Videos.bash_historyDesktop.local.sudo_as_admin_successful.bash_logout Documents.mozillaTemplates.bashrcDownloadsMusic .thunderbird.cache .emacs.d .profile.tldrdemo DocumentsMusic Templates VideosDesktopDownloadsPublictypescriptdemo: directoryfile demo.cdemo.c: C source, ASCII textcat demo.c#include

int main() {
printf(welcome to git demo!
);
printf(Nice to meet you!);
alias alert=notify-send urgency=low -i $([ $? = 0 ] && echo terminal || echo error) $(history|tail -n1|sed -e s/^s*[0-9]+s*//;s/[;&|]s*alert$//)
alias egrep=egrep color=auto
alias fgrep=fgrep color=auto
alias grep=grep color=auto
alias l=ls -CF
alias la=ls -A
alias ll=ls -alF
alias ls=ls color=auto
alias deepdir=mkdir a; cd a; mkdir b; cd b; mkdir c; cd c
alias alert=notify-send urgency=low -i $([ $? = 0 ] && echo terminal || echo error) $(history|tail -n1|sed -e s/^s*[0-9]+s*//;s/[;&|]s*alert$//)
alias deepdir=mkdir a; cd a; mkdir b; cd b; mkdir c; cd c
alias egrep=egrep color=auto
alias fgrep=fgrep color=auto
alias grep=grep color=auto
alias l=ls -CF
alias la=ls -A
alias ll=ls -alF
alias ls=ls color=auto
mkdir: cannot create directory a: File exists
mkdir: cannot create directory b: File exists
mkdir: cannot create directory c: File exists
rmdir: failed to remove a: Directory not empty
type deepdir
deepdir is aliased to `mkdir a; cd a; mkdir b; cd b; mkdir c; cd c
unalias deepdir
type deepdir
bash: type: deepdir: not found
demo DocumentsMusic Templates Videos
DesktopDownloadsPublictypescript
rmdir Videos
mkdir Videos
demo DocumentsMusic Templates Videos
DesktopDownloadsPublictypescript
cp /etc/passwd x
x: ASCII text
cp /etc/passwd Documents/
ls Documents/
cp /etc/passwd Documents/mypasswd
ls -l Documents/
-rw-rr 1 neo neo 2744 Feb2 07:50 mypasswd
-rw-rr 1 neo neo 2744 Feb2 07:49 passwd
mv Documents Templates/
demoDesktopDownloadsMusicPublicTemplatestypescriptVideosx
ls Templates/
ls Templates/Documents/
mypasswdpasswd

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