Command features
- > :- Redirect output
- >> :- Append to file
- < :- Redirect input
- << :- "Here" document (redirect input)
- | :- Pipe output
- & :- Run process in background.
- ; :- Separate commands on same line
- * :- Match any character(s) in filename
- ? :- Match single character in filename
- [ ] :- Match any characters enclosed
- ( ) :- Execute in subshell
- ` ` :- Substitute output of enclosed command
- " " :- Partial quote (allows variable and command expansion)
- ' ' :- Full quote (no expansion)
- \ :- Quote following character
- $var :- Use value for variable
- $$ :- Process id
- $0 :- Command name
- $n :- nth argument (n from 0 to 9)
- $* :- All arguments as a simple word
- # :- Begin comment
- bg :- Background execution
- break :- Break from loop statements
- cd :- Change directories
- cont :- Resume a program loop
- echo :- Display output
- eval :- Evaluate arguments
- exec :- Execute a new shell
- fg :- Foreground execution
- jobs :- Show active jobs
- kill :- Terminate running jobs
- newgrp :- Change to a new group
- shift :- Shift positional parameters
- stop :- Suspend a background job
- suspend :- Suspend a foreground job
- time :- Time a command
- umask :- Set or list file permissions
- unset :- Erase variable or function definitions
- wait :- Wait for a background job to finish
