Bash Shell Quick Reference

Note: This document was translated from portuguese to english by Luiz Miguel Axcar.

1. Operators

Arithmetic Operators
+ Addition
- Subtraction
* Multiplication
/ Division
% Modulo
** Exponentiation
Attribution Operators
= Attribute some value to a variable
+= Increase a variable with a constant
-= Decrease a variable with a constant
*= Multiply the variable by a constant
/= Divide a variable by a constant
%= Remainder of division by a constant
++ Increase 1 to the variable value
-- Decrease 1 from the variable value
Comparison Operators
== Equals
!= Not equals to (different)
> Greater than
>= Greater than or equal to
< Less than
<= Less than or equal to
Logical Operators
&& Logical AND
|| Logical OR
Bitwise Operators
<< Left-shift
>> Right-shift
& Bitwise AND
| Bitwise OR
^ Bitwise Exclusive OR (XOR)
~ Bitwise NOT (complement)
! NOT
Bitwise Operators (attribution)
<<= Left-shift
>>= Right-shift
&= Bitwise AND
|= Bitwise OR
^= Bitwise Exclusive OR (XOR)

2. Redirection

Operator Action
< Redirect the standard input (STDIN)
> Redirect the standard output (STDOUT)
2> Redirect the error output (STDERR)
>> Redirect the standard output, appending
2>> Redirect the error output, appending
| Connects the standard output with standard input of another command
2>&1 Connects the error output with standard output
>&2 Connects the standard output with error output
>&- Closes the standard output
2>&- Closes the error output
3<>file Connects the file descriptor 3 to file 'file'
<<FIM Feeds the standard input (Here Document)
<<-FIM Feeds the standard input, striping TABs
<(cmd) The output of command 'cmd' is a file: diff <(cmd1) <(cmd2)
>(cmd) The input of command 'cmd' is a file: tar cf >(bzip2 -c >file.tbz) $dir

3. Special variables

Variable Positioning parameters
$0 Parameter #0 (name of command or function)
$1 Parameter #1 (from command line or function)
... Parameter #N ...
$9 Parameter #9 (from command line or function)
${10} Parameter #10 (from command line or function)
... Parameter #NN ...
$# Total number of parameters from command line or function
$* All the parameters, in a single string
$@ All the parameters, in many protected strings
Variable Misc
$$ PID of current process (or script)
$! PID of last job in background
$_ Last argument of last executed command
$? Error code of last executed command

4. Variable expansion

Syntax Conditional Expansion
${var:-text} If var is undefined, returns 'text'
${var:=text} If var is undefined, set as 'text'
${var:?text} If var is undefined, returns error message 'text'
${var:+text} If var is defined, returns 'text', else return empty
Syntax String expansion
${var} Is the same of $var, but not ambiguous
${#var} Return the string length
${!var} Executes the content of $var (like 'eval \$$var')
${!text*} Return the names of variables starting with 'text'
${var:N} Return the text from position 'N'
${var:N:len} Return 'len' chars from position 'N'
${var#text} Cut 'text' from beginning of string
${var##text} Cut 'text' from beginning of string (*greedy)
${var%text} Cut 'text' from end of string
${var%%text} Cut 'text' from end of string (*greedy)
${var/text/new} Replace 'text' by 'new', once
${var//text/new} Replace 'text' by 'new', all
${var/#text/new} If string starts with 'text', replace 'text' by 'new'
${var/%text/new} If string ends with 'text', replace 'text' by 'new'

5. Quoting and grouping

Syntax Description Example
"..." Protects a string, but parse $, \ and ` as special chars "abc"
'...' Protects a string completely (no special chars recognized) 'abc'
$'...' Protects a string completely, but interprets \n, \t, \a, etc $'abc\n'
`...` Execute commands in a subshell, returning the result `ls`
{...} Group commands { ls ; }
(...) Execute commands in a subshell ( ls )
$(...) Execute commands in a subshell, returning the result $( ls )
((...)) Test an arithmetic operation, returning 0 or 1 ((5 > 3))
$((...)) Return the result of a arithmetic operation $((5+3))
[...] Test an arithmetic expression, returning 0 or 1 (alias of command 'test') [ 5 -gt 3 ]
[[...]] Test an expression, returning 0 or 1 (&& and || are allowed) [[ 5 > 3 ]]

6. if, for, select, while, until, case

if for / select while / until case
if COMMAND
then
   ...
elif COMMAND
then
   ...
else
   ...
fi
for VAR in LIST
do
    ...
done

or:

for ((exp1;exp2;exp3))
while COMMAND
do
    ...
done
case $VAR in
    txt1) ... ;;
    txt2) ... ;;
    txtN) ... ;;
    *)    ... ;;
esac

7. test or [ … ]

Numeric comparison
-lt Less Than
-gt Greater than
-le Less than or Equal to
-ge Greater than or Equal to
-eq Equals
-ne Not Equal to (different)
String comparison
= Equals
!= Not Equal to (different)
-n Not NULL
-z Is NULL
Logical Operators
! Logical NOT
-a Logical AND
-o Logical OR
Testing files
-b Is a block device
-c Is a char device
-d Is a directory
-e File exists
-f Is a regular file
-g SGID bit is switched on
-G Current user is in the file's group
-k Sticky-bit is switched on
-L File is a symlink
-O Current user owns the file
-p File is a named pipe
-r File has read permission
-s File size is greater than zero
-S File is a socket
-t File descriptor N is a terminal
-u SUID bit is switched on
-w File has write permission
-x File has execution permission
-nt File is Newer Than
-ot File is Older Than
-ef File is the same - Equal File

8. Prompt escapes ($PS1)

Escape Reminder Expands to...
\a Alert Alert (beep)
\d Date Date in format "Week-day Month Day" (Sat Jan 15)
\e Escape Esc character
\h Hostname Hostname without the domain (dhcp11)
\H Hostname Full hostname (dhcp11.company)
\j Jobs Number of active jobs
\l Tty Name of current terminal (ttyp1)
\n Newline New Line
\r Return Carriage return
\s Shell Shell name (basename $0)
\t Time Time in 24 hours format HH:MM:SS
\T Time Time in 12 hours format HH:MM:SS
\@ At Time in 12 hours format HH:MM am/pm
\A At Time in 24 hours format HH:MM
\u User Current user login
\v Version Bash Version (2.00)
\V Version Bash Version + Subversion (2.00.0)
\w Working Dir Full working dir ($PWD)
\W Working Dir Last working dir (basename $PWD)
\! History Number of current command in history
\# Number Number of current command
\$ ID Show "#" if user is root, and "$" in case of a regular user
\nnn Octal Char which Octal value is nnn
\\ Backslash Backslash \ literal
\[ Escapes Start a escape sequence (color codes)
\] Escapes Finish a escape sequence

9. echo escapes

Escape Reminder Description
\a Alert Alert (beep)
\b Backspace Backspace character
\c EOS Ends the string
\e Escape Esc character
\f Form feed Form Feed
\n Newline Newline
\r Return Carriage Return
\t Tab Tab
\v Vtab Vertical Tab
\\ Backslash Backslash
\nnn Octal Character whose octal code is nn
\xnn Hexa Character whose hexadecimal code is nn

10. date tokens

Format Description
%a Day of the week - abbreviated name (Sun..Sat)
%A Day of the week - full name (Sunday..Saturday)
%b Month name - abbreviated (Jan..Dec)
%B Month name - full (January..December)
%c Locale's date and time (Thu 05 May 2011 11:41:41 AM EST)
%y Year (two digits)
%Y Year (four digits)
%m Month (01..12)
%d Day (01..31)
%j Day of year (001..366)
%H Hours (00..23)
%M Minutes (00..59)
%S Seconds (00..60)
%s Seconds since 00:00:00, Jan 1, 1970 (Unix time)
%% A literal %
%t A TAB
%n A newline

11. printf tokens

Format Description
%d Integer number
%o Octal number
%x Hexadecimal Number (a-f)
%X Hexadecimal Number (A-F)
%f Float number
%e Scientific notation x.xxxx e nnn. float, double (e+1)
%E Same as %e, but with an upper-case E in the printed format
%s String

12. ls -l file identifiers

Letter Reminder File types (First char)
- - Regular file
d Directory Directory
l Link Symbolic link
b Block Block Device (Hard drives)
c Char Character device (serial modem)
s Socket Mapped socket in a file (processes communication)
p Pipe FIFO or Named Pipe (processes communication)
Letter Reminder File permission (next nine chars)
- - Deactivated
r Read Read Permission
w Write Write permission
x eXecute Execution permission (or directory access)
X eXecute Directory access only
s Set ID User/group for execution (SUID, SGID) - permission 'x' activated
S Set ID User/group for execution (SUID, SGID) - permission 'x' deactivated
t sTicky Users delete his own files only - permission 'x' activated
T sTicky Users delete his own files only - permission 'x' deactivated

13. Filenames wildcards (glob)

Wildcard Matches... Example
* Anything *.txt
? Any char file-??.zip
[...] Any char in the group [Ff]ile.txt
[^...] Any char, except those in the group [^A-Z]*.txt
{...} Any text, comma separated file.{txt,html}

14. case wildcards

Wildcard Matches... Example
* Anything *.txt) echo ;;
? Any char file-??.zip) echo ;;
[...] Any char in the group [0-9]) echo ;;
[^...] Any char, except those in the group [^0-9]) echo ;;
...|... Ant text, pipe separated txt|html) echo ;;

15. trap/kill/killall signals

# Linux Cygwin SystemV AIX HP-UX Solaris BSD/Mac
1 HUP HUP HUP HUP HUP HUP HUP
2 INT INT INT INT INT INT INT
3 QUIT QUIT QUIT QUIT QUIT QUIT QUIT
4 ILL ILL ILL ILL ILL ILL ILL
5 TRAP TRAP TRAP TRAP TRAP TRAP TRAP
6 ABRT ABRT IOT LOST ABRT ABRT ABRT
7 BUS EMT EMT EMT EMT EMT EMT
8 FPE FPE FPE FPE FPE FPE FPE
9 KILL KILL KILL KILL KILL KILL KILL
10 USR1 BUS BUS BUS BUS BUS BUS
11 SEGV SEGV SEGV SEGV SEGV SEGV SEGV
12 USR2 SYS SYS SYS SYS SYS SYS
# Linux Cygwin SystemV AIX HP-UX Solaris BSD/Mac
13 PIPE PIPE PIPE PIPE PIPE PIPE PIPE
14 ALRM ALRM ALRM ALRM ALRM ALRM ALRM
15 TERM TERM TERM TERM TERM TERM TERM
16 - URG USR1 URG USR1 USR1 URG
17 CHLD STOP USR2 STOP USR2 USR2 STOP
18 CONT TSTP CHLD TSTP CHLD CHLD TSTP
19 STOP CONT PWR CONT PWR PWR CONT
20 TSTP CHLD WINCH CHLD VTALRM WINCH CHLD
21 TTIN TTIN URG TTIN PROF URG TTIN
22 TTOU TTOU IO TTOU IO IO TTOU
23 URG IO STOP IO WINCH STOP IO
24 XCPU XCPU TSTP XCPU STOP TSTP XCPU
# Linux Cygwin SystemV AIX HP-UX Solaris BSD/Mac
25 XFSZ XFSZ CONT XFSZ TSTP CONT XFSZ
26 VTALRM VTALRM TTIN - CONT TTIN VTALRM
27 PROF PROF TTOU MSG TTIN TTOU PROF
28 WINCH WINCH VTALRM WINCH TTOU VTALRM WINCH
29 IO LOST PROF PWR URG PROF INFO
30 PWR USR1 XCPU USR1 LOST XCPU USR1
31 SYS USR2 XFSZ USR2 - XFSZ USR2
32 - - - PROF - WAITING -
33 - - - DANGER - LWP -
34 - - - VTALRM - FREEZE -
35 - - - MIGRATE - THAW -
36 - - - PRE - CANCEL -
37 - - - - - LOST -

How you can get this list: trap -l, kill -l or killall -l
See also: man 7 signal

16. Exit codes

Code Meaning Example
0 No errors echo
1 Catchall for most common errors echo $((1/0))
2 Misuse of shell builtins -
126 Command cannot be executed (no permission) touch a ; ./a
127 Command not found echooo
128 Invalid argument to exit exit 1.0
128+n 128 + exit code which was killed kill -9 $PPID #exit 137
130 Script terminated by Ctrl+C (128 + 2) -
255 'exit' parameter not between 0 and 255 exit -1

17. Color codes (ANSI)

Color Letter Background
Black 30 40
Red 31 41
Green 32 42
Yellow 33 43
Blue 34 44
Pink 35 45
Cyan 36 46
White 37 47
Attribute Value
Reset 0
Bold 1
Underline 4
Blinking 5
Reverse 7
Examples: ESC [ <N>;<N> m
Regular text (Turn color off) ESC[m
Bold ESC[1m
Yellow ESC[33;1m
Blue background, gray letter ESC[44;37m
Blinking red ESC[31;5m
On the command line
echo -e '\e[33;1m yellow \e[m'
echo -e '\033[33;1m yellow \033[m'

18. Regex metacharacters

Meta Name Description
. Dot Matches exactly one char (any char)
[] List Matches any char in the group
[^] Negated list Matches any char, except those in the group
? Optional Matches the preceding item zero or one time
* Star Matches the preceding item zero or more times
+ Plus Matches the preceding item one or more times
{,} Repeat Matches the preceding item between m and n times {m,n}
^ Caret Matches the start of the line
$ Dollar Matches the end of the line
\b Boundary Matches the word boundary
\ Escape Escapes a metacharacter, taking off its power
| OR Alternatives (use inside a group)
() Group Group slices of expression, nesting is allowed
\1 Backreference Returns group #1 contents
\2 Backreference Returns group #2 contents (until \9)
.* Catchall Matches everything, even nothing
?? Lazy Optional Like regular Optional, but not greedy
*? Lazy Star Like regular Star, but not greedy
+? Lazy Plus Like regular Plus, but not greedy
{}? Lazy Repeat Like regular Repeat, but not greedy

19. Regex flavors

Program Opt Plus Repeat Boundary OR Group
awk ? + - - | ()
ed \? \+ \{,\} \b \| \(\)
egrep ? + {,} \b | ()
emacs ? + - \b \| \(\)
expect ? + - - | ()
find ? + - \b \| \(\)
gawk ? + {,} \<\> | ()
grep \? \+ \{,\} \b \| \(\)
mawk ? + - - | ()
perl ? + {,} \b | ()
php ? + {,} \b | ()
python ? + {,} \b | ()
sed \? \+ \{,\} \<\> \| \(\)
vim \= \+ \{,} \<\> \| \(\)

20. Printable ASCII characters (ISO-8859-1) - text

32        64  @     96  `    162  ¢    194  Â    226  â
33  !     65  A     97  a    163  £    195  Ã    227  ã
34  "     66  B     98  b    164  ¤    196  Ä    228  ä
35  #     67  C     99  c    165  ¥    197  Å    229  å
36  $     68  D    100  d    166  ¦    198  Æ    230  æ
37  %     69  E    101  e    167  §    199  Ç    231  ç
38  &     70  F    102  f    168  ¨    200  È    232  è
39  '     71  G    103  g    169  ©    201  É    233  é
40  (     72  H    104  h    170  ª    202  Ê    234  ê
41  )     73  I    105  i    171  «    203  Ë    235  ë
42  *     74  J    106  j    172  ¬    204  Ì    236  ì
43  +     75  K    107  k    173       205  Í    237  í
44  ,     76  L    108  l    174  ®    206  Î    238  î
45  -     77  M    109  m    175  ¯    207  Ï    239  ï
46  .     78  N    110  n    176  °    208  Ð    240  ð
47  /     79  O    111  o    177  ±    209  Ñ    241  ñ
48  0     80  P    112  p    178  ²    210  Ò    242  ò
49  1     81  Q    113  q    179  ³    211  Ó    243  ó
50  2     82  R    114  r    180  ´    212  Ô    244  ô
51  3     83  S    115  s    181  µ    213  Õ    245  õ
52  4     84  T    116  t    182  ¶    214  Ö    246  ö
53  5     85  U    117  u    183  ·    215  ×    247  ÷
54  6     86  V    118  v    184  ¸    216  Ø    248  ø
55  7     87  W    119  w    185  ¹    217  Ù    249  ù
56  8     88  X    120  x    186  º    218  Ú    250  ú
57  9     89  Y    121  y    187  »    219  Û    251  û
58  :     90  Z    122  z    188  ¼    220  Ü    252  ü
59  ;     91  [    123  {    189  ½    221  Ý    253  ý
60  <     92  \    124  |    190  ¾    222  Þ    254  þ
61  =     93  ]    125  }    191  ¿    223  ß    255  ÿ
62  >     94  ^    126  ~    192  À    224  à
63  ?     95  _    161  ¡    193  Á    225  á

21. Printable ASCII characters (ISO-8859-1) - image

22. Copy-paste friendly commands

Conditions with IF
if [ -f "$file" ]; then echo 'File found'; fi
if [ ! -d "$dir" ]; then echo 'Directory not found'; fi
if [ $i -gt 5 ]; then echo 'Greater than 5'; else echo 'Lesser than 5'; fi
if [ $i -ge 5 -a $i -le 10 ]; then echo 'Between 5 and 10, inclusive'; fi
if [ $i -eq 5 ]; then echo '=5'; elif [ $i -gt 5 ]; then echo '>5'; else echo '<5'; fi
if [ "$USER" = 'root' ]; then echo 'Hello root'; fi
if grep -qs 'root' /etc/passwd; then echo 'User found'; fi
Conditions with AND (&&) and OR (||)
[ -f "$file" ] && echo 'File found'
[ -d "$dir" ] || echo 'Directory not found'
grep -qs 'root' /etc/passwd && echo 'User found'
cd "$dir" && rm "$file" && touch "$file" && echo 'done!'
[ "$1" ] && param=$1 || param='default value'
[ "$1" ] && param=${1:-default value}
[ "$1" ] || { echo "Usage: $0 parameter" ; exit 1 ; }
Adds 1 to variable $i
i=$(expr $i + 1)
i=$((i+1))
let i=i+1
let i+=1
let i++
Loop from 1 to 10
for i in 1 2 3 4 5 6 7 8 9 10; do echo $i; done
for i in $(seq 10); do echo $i; done
for ((i=1;i<=10;i++)); do echo $i; done
i=1 ; while [ $i -le 10 ]; do echo $i ; i=$((i+1)) ; done
i=1 ; until [ $i -gt 10 ]; do echo $i ; i=$((i+1)) ; done
Loop reading lines from a file or command output
cat /etc/passwd | while read LINE; do echo "$LINE"; done
grep 'root' /etc/passwd | while read LINE; do echo "$LINE"; done
while read LINE; do echo "$LINE"; done < /etc/passwd
while read LINE; do echo "$LINE"; done < <(grep 'root' /etc/passwd)
Wildcards for case command
case "$dir" in /home/*) echo 'dir inside /home';; esac
case "$user" in root|john|mary) echo "Hello $user";; *) echo "I don't know you.";; esac
case "$var" in ?) echo '1 letter';; ??) echo '2 letters';; ??*) echo 'More than 2 letters';; esac
case "$i" in [0-9]) echo '1 digit';; [0-9][0-9]) echo '2 digits';; esac
Dialog boxes
dialog --calendar 'abc' 0 0 31 12 1999
dialog --checklist 'abc' 0 0 0 item1 'desc1' on item2 'desc2' off
dialog --fselect /tmp 0 0
(echo 50; sleep 2; echo 100) | dialog --gauge 'abc' 8 40 0
dialog --infobox 'abc' 0 0
dialog --inputbox 'abc' 0 0
dialog --passwordbox 'abc' 0 0
dialog --menu 'abc' 0 0 0 item1 'desc1' item2 'desc2'
dialog --msgbox 'abc' 8 40
dialog --radiolist 'abc' 0 0 0 item1 'desc1' on item2 'desc2' off
dialog --tailbox /tmp/file.txt 0 0
dialog --textbox /tmp/file.txt 0 0
dialog --timebox 'abc' 0 0 23 59 00
dialog --yesno 'abc' 0 0
Hint 1: Dialog ... && echo 'You pressed OK/Yes' || echo 'You pressed Cancel/No'
Hint 2: result=$(Dialog --stdout --BOXTYPE 'abc' ...)

23. Command line shortcuts (set -o emacs)

Shortcut Description Similar key
Ctrl+A Move the cursor to the beginning of line Home
Ctrl+B Move the cursor one position left
Ctrl+C Send EOF() to the system
Ctrl+D Delete the char at right Delete
Ctrl+E Move the cursor to the end of line End
Ctrl+F Move the cursor one position at right
Ctrl+H Delete the char at left Backspace
Ctrl+I Complete files and commands Tab
Ctrl+J Line break Enter
Ctrl+K Cut from cursor to the end of line
Ctrl+L Clear screen
Ctrl+N Next command
Ctrl+P Previous command
Ctrl+Q Unlock the shell (see Ctrl+S)
Ctrl+R Seek in the command history
Ctrl+S Lock the shell (see Ctrl+Q)
Ctrl+T Exchange two chars position
Ctrl+U Cut the whole line
Ctrl+V Insert a literal character
Ctrl+W Cut word at left
Ctrl+X Move the cursor to end/beginning of line (2x) Home/End
Ctrl+Y Paste the text

24. Toolbox

Command Function Useful options
cat Show file contents -n, -s
cut Extract fields -d -f, -c
date Show date -d, +'...'
diff Compare files -u, -Nr, -i, -w
echo Show text -e, -n
find Find files -name, -iname, -type f, -exec, -or
fmt Format paragraph -w, -u
grep Search for text -i, -v, -r, -qs, -n, -l, -w -x, -A -B -C
head Show first lines -n, -c
od Show chars -a, -c, -o, -x
paste Merge files -d, -s
printf Show text nothing
rev Reverse text nothing
sed Edit text -n, -f, s/this/that/, p, d, q, N
seq Count numbers -s, -f
sort Sort text -n, -f, -r, -k -t, -o
tac Reverse file nothing
tail Show last lines -n, -c, -f
tee Save the stream -a
tr Transforms the text -d, -s, A-Z a-z
uniq Remove duplicated -i, -d, -u
wc Count letters -c, -w, -l, -L
xargs Manage arguments -n, -i
— EOF —
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