Bash Operators

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Process Management Operators

Symbol	Meaning	Example
&	Run in background	sleep 10 &
&&	Run next only if previous succeeds	mkdir newdir && cd newdir
;	Run multiple commands sequentially	echo "Hello"; echo "World"
()	Run in a subshell (isolated environment)	(cd /tmp; ls)
{}	Group commands in current shell	{ cd /tmp; ls; }
|	Pipe output of one command into another	`ls -l

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Variable & Expansion Operators

Symbol	Meaning	Example
$VAR	Expands variable	echo $HOME
$$	PID of current shell	echo $$
$!	PID of last background process	sleep 60 & echo $!
$?	Exit status of last command	ls /bad && echo $?
$0	Script name	echo $0
$1, $2, ...	Positional arguments	./script.sh arg1 → $1 = arg1
$#	Number of args passed	echo $#
$@	All args as separate strings	for arg in "$@"; do echo $arg; done
$*	All args as one string	echo "$*"
${VAR}	Explicit expansion	echo "Path: ${HOME}/bin"
${VAR:-default}	Use default if unset	echo ${NAME:-Guest}

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Input / Output Redirection

Symbol	Meaning	Example
>	Redirect stdout (overwrite)	echo "Hi" > file.txt
>>	Redirect stdout (append)	echo "More" >> file.txt
<	Read from file	wc -l < file.txt
2>	Redirect stderr	ls /bad 2> error.log
&>	Redirect stdout + stderr	mycmd &> all.log
`>	`	Overwrite even with noclobber
tee	Output to file and stdout	`echo "Log"

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String & Pattern Matching

Symbol	Meaning	Example
*	Match any number of characters	ls *.txt
?	Match one character	ls file?.txt
[...]	Match any in set	ls file[123].txt
[^...]	Match any NOT in set	ls file[^123].txt
{A,B}	Expand to A, B	echo {red,blue}.jpg
{1..5}	Expand numeric sequence	echo file{1..5}.txt

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Command Substitution

Syntax	Meaning	Example
`command`	Replace with command output	echo `date`
$(command)	Same, supports nesting	echo $(date)

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Quotes & Escaping

Symbol	Meaning	Example
'...'	Strong quote, no expansion	echo '$HOME'
"..."	Weak quote, allows expansion	echo "$HOME"
\	Escape character	echo \"Hello\"
\n	Newline (used with echo -e)	echo -e "Hi\nThere"

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Special Built-in Commands

Symbol	Meaning	Example
:	No-op (does nothing)	: && echo "Continues"
true	Always succeeds	true && echo "Success"
false	Always fails	`false
exit	Exit shell with status	exit 1
exec	Replace shell with command	exec ls
source	Run script in current shell	source ~/.bashrc

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Loops & Conditionals

Syntax	Meaning	Example
if ... then ... fi	Conditional block	if [ -f file ]; then echo "Yes"; fi
[ ... ]	Basic test	[ -d /home ] && echo "Exists"
[[ ... ]]	Extended test	[[ "x" == "x" ]] && echo "Match"
for ... in ...	Loop over list	for i in {1..3}; do echo $i; done
while ...	Loop while condition	while true; do echo "Hi"; sleep 1; done

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Background & Job Control

Symbol	Meaning	Example
&	Run in background	sleep 10 &
jobs	List background jobs	jobs
fg	Resume job in foreground	fg %1
bg	Resume job in background	bg %1
nohup	Run after logout	nohup script.sh &
disown	Remove from job table	disown %1

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TL;DR: Essential Symbols

✔ Process control:     &, &&, ||, ()
✔ Variables:           $, $$, $!, $@
✔ Redirection:         >, <, 2>, |
✔ Patterns:            *, ?, {}
✔ Quoting:             '...', "...", \
✔ Job control:         jobs, fg, bg, disown