Bash Quick Reference

Syntax refreshers

---

Control Flow Operators

Operator	Equivalent
$a -lt $b	$a < $b
$a -gt $b	$a > $b
$a -le $b	$a <= $b
$a -ge $b	$a >= $b
$a -eq $b	$a is equal to $b
$a -ne $b	$a is not equal to $b

---

File Test Operators

Operator	Condition checked	return result
-b file	Checks if file is a block special file; if yes, then the condition becomes true.	[ -b $file ] is false.
-c file	Checks if file is a character special file; if yes, then the condition becomes true.	[ -c $file ] is false.
-d file	Checks if file is a directory; if yes, then the condition becomes true.	[ -d $file ] is not true.
-f file	Checks if file is an ordinary file as opposed to a directory or special file; if yes, then the condition becomes true.	[ -f $file ] is true.
-g file	Checks if file has its set group ID (SGID) bit set; if yes, then the condition becomes true.	[ -g $file ] is false.
-k file	Checks if file has its sticky bit set; if yes, then the condition becomes true.	[ -k $file ] is false.
-p file	Checks if file is a named pipe; if yes, then the condition becomes true.	[ -p $file ] is false.
-t file	Checks if file descriptor is open and associated with a terminal; if yes, then the condition becomes true.	[ -t $file ] is false.
-u file	Checks if file has its Set User ID (SUID) bit set; if yes, then the condition becomes true.	[ -u $file ] is false.
-r file	Checks if file is readable; if yes, then the condition becomes true.	[ -r $file ] is true.
-w file	Checks if file is writable; if yes, then the condition becomes true.	[ -w $file ] is true.
-x file	Checks if file is executable; if yes, then the condition becomes true.	[ -x $file ] is true.
-s file	Checks if file has size greater than 0; if yes, then condition becomes true.	[ -s $file ] is true.
-e file	Checks if file exists; is true even if file is a directory but exists.	[ -e $file ] is true.
-z file	Checks if a string is empty "" and evaluates to true if it is	str=""; [ -z $str ] is true

---

Special Variables

Variable	Description
$0	The filename of the current script.
$n	These variables correspond to the arguments with which a script was invoked. Here n is a positive decimal number corresponding to the position of an argument (the first argument is $1, the second argument is $2, and so on).
$#	The number of arguments supplied to a script.
$*	All the arguments are double quoted. If a script receives two arguments, $* is equivalent to $1 $2.
$@	All the arguments are individually double quoted. If a script receives two arguments, $@ is equivalent to $1 $2.
$?	The exit status of the last command executed.
$$	The process number of the current shell. For shell scripts, this is the process ID under which they are executing.
$!	The process number of the last background command.

---

ANSI Escape Color Codes

Regular Colors

Value	Color
\e[0;30m	Black
\e[0;31m	Red
\e[0;32m	Green
\e[0;33m	Yellow
\e[0;34m	Blue
\e[0;35m	Purple
\e[0;36m	Cyan
\e[0;37m	White

Bold

Value	Color
\e[1;30m	Black
\e[1;31m	Red
\e[1;32m	Green
\e[1;33m	Yellow
\e[1;34m	Blue
\e[1;35m	Purple
\e[1;36m	Cyan
\e[1;37m	White

Underline

Value	Color
\e[4;30m	Black
\e[4;31m	Red
\e[4;32m	Green
\e[4;33m	Yellow
\e[4;34m	Blue
\e[4;35m	Purple
\e[4;36m	Cyan
\e[4;37m	White

Background

Value	Color
\e[40m	Black
\e[41m	Red
\e[42m	Green
\e[43m	Yellow
\e[44m	Blue
\e[45m	Purple
\e[46m	Cyan
\e[47m	White

High Intensty

Value	Color
\e[0;90m	Black
\e[0;91m	Red
\e[0;92m	Green
\e[0;93m	Yellow
\e[0;94m	Blue
\e[0;95m	Purple
\e[0;96m	Cyan
\e[0;97m	White

Bold High Intensty

Value	Color
\e[1;90m	Black
\e[1;91m	Red
\e[1;92m	Green
\e[1;93m	Yellow
\e[1;94m	Blue
\e[1;95m	Purple
\e[1;96m	Cyan
\e[1;97m	White

High Intensty backgrounds

Value	Color
\e[0;100m	Black
\e[0;101m	Red
\e[0;102m	Green
\e[0;103m	Yellow
\e[0;104m	Blue
\e[0;105m	Purple
\e[0;106m	Cyan
\e[0;107m	White

Reset

Value	Color
\e[0m	Reset

---

Bash Prompt Escape sequences

          \a     an ASCII bell character (07)
          \d     the date  in  "Weekday  Month  Date"  format
                 (e.g., "Tue May 26")
          \e     an ASCII escape character (033)
          \h     the hostname up to the first `.'
          \H     the hostname
          \j     the  number of jobs currently managed by the
                 shell
          \l     the basename of the shell's terminal  device
                 name
          \n     newline
          \r     carriage return
          \s     the  name  of  the shell, the basename of $0
                 (the portion following the final slash)
          \t     the current time in 24-hour HH:MM:SS format
          \T     the current time in 12-hour HH:MM:SS format
          \@     the current time in 12-hour am/pm format
          \u     the username of the current user
          \v     the version of bash (e.g., 2.00)
          \V     the release of bash,  version  +  patchlevel
                 (e.g., 2.00.0)
          \w     the current working directory
          \W     the  basename  of the current working direc­
                 tory
          \!     the history number of this command
          \#     the command number of this command
          \$     if the effective UID is 0, a #, otherwise  a
                 $
          \nnn   the  character  corresponding  to  the octal
                 number nnn
          \\     a backslash
          \[     begin a sequence of non-printing characters,
                 which could be used to embed a terminal con­
                 trol sequence into the prompt
          \]     end a sequence of non-printing characters