linuxcli.md

commands

• touch: create file
• ls: list of files
• cd: change directory home dir: ~ parent dir: .. current dir: .
• pwd: display current directory
• mkdir: make directory
• ls -a: view list of files with hidden files
• cat: read files
• grep (searchstring) (directory): to find text within a file
• find (path) -name (filename): to find files within directories
• ln -s (original file loc) (new loc): for symlinking files a hardlink is a link which refers to two different names for a specific physical place a softlink is like creating a new fwding address for the previously located physical place
• man: to read manual page for a command to search in a manual page use / man man to get man command's man page man -k (text) to search for a command within a man page
• (command) --help: to know how to details about a command you can run help for builtins using help (command)
• echo: outputs str as passed to it

file globbing

• ? for one char
• * for multiple char, wildcard
• [abc] for limited chars within brackets
• [^abc] for all chars except those in brackets

piping

• redirecting output from file desrciptor to file: >

• redirecting output in append mode >>

• redirect stdout 1> same as >

• redirecting stderr 2>

• redirecting input <

• to avoid storing a file, you can pipe the output using |

• you can redirect from file descriptor to file descriptor using >&

• you can use | tee (1) (2) to save the middleman output of what is happening in halfway stage of running your command by saving it to a file or saving an error/result midway

shell variables

• echo $VAR to read variables
• VAR=value to set value
• multi word vars, use ""
• export VAR=value to save value of variable so future shell programs inherit the value
• env: to print every exported var
• to save output of command into var: VAR=$(program)
• read to read files directly instead of using cat

processes

• ps or ps aux to list all running processes
• kill to kill processes
• ctrl+c to interrupt process
• suspend into bg ctrl+z
• fg to foreground a process
• bg to resume in background
• to start processes backgrounded from the start use sleep processid &
• echo $? to read exit code of process

misc

• su (user) then enter pass to login, use tool johntheripper
• sudo to exec as root
• semicolon to chain commands
• export PATH=xyz:$PATH to append to path

perms

• chown (user) (filedir) to change ownership
• chgrp for changing groups
• id to identify which users groups have permissions to use the file
• chmod (u or g or o) (+ or -) (r or w or x) (filedir)
• chmod u=rx,g=rx (filedir) using commas and = can also be done
• chmod u+s (programdir) to add it to SUID bit