cheatsheets

bash-cheatsheet

 ____    _    ____  _   _    ____ _                _       _               _
| __ )  / \  / ___|| | | |  / ___| |__   ___  __ _| |_ ___| |__   ___  ___| |_
|  _ \ / _ \ \___ \| |_| | | |   | '_ \ / _ \/ _` | __/ __| '_ \ / _ \/ _ \ __|
| |_) / ___ \ ___) |  _  | | |___| | | |  __/ (_| | |_\__ \ | | |  __/  __/ |_
|____/_/   \_\____/|_| |_|  \____|_| |_|\___|\__,_|\__|___/_| |_|\___|\___|\__|

kelvinchan.ca

Comparison
==========

test    test command                            &&      logic AND
[ ]     synonym for test command                ||      logic OR
[[ ]]   extended test                           !       logic NOT
let     evaluate arithmetic expression
(( ))   same as above

File Test Operators                             Integer Test Operators
-------------------                             ----------------------

-f      is a regular file?                      -eq     is equal to?
-d      is directory?                           -ne     is not equal to?
-b      is block device?                        -gt     is greater than?
-c      is char device?                         -ge     is greater than or equal to?
-p      is pipe?                                -lt     is less than?
-h      is symlink?                             -le     is less than or equal to?
-S      is socket?
-t      is fd associated with                   Arithmetic Test Operators
        a terminal device?                      -------------------------

-e      file exists?                            <       is less than?
-s      is zero size?                           <=      is less than or equal to?
                                                >       is greater than?
-r      has read permission?                    >=      is greater than or equal to?
-w      has write permission?
-x      has execute permission?                 String Test Operators
-g      is sgid flag set?                       ---------------------
-u      is suid flag set?
-k      is sticky bit set?                      =       is equal to?
-O      are you the owner?                      ==      is equal to? (synonym for =)
-G      are you in the same group?              !=      is not equal to?
-N      is modified since last read?            =~      matches extended regex?
-nt     is newer than?                          <       is less than? (in ASCII order)
-ot     is older than?                          >       is greater than? (in ASCII order)
-ef     is hard linked to?                      -z      is null or zero lengh?
                                                -n      is not null?

Shell Parameters                                Common Shell Variables
================                                ======================

$n  the n-th positional param                   $TMPDIR     temp directory
    ($0 is the name of the command)             $PS3        prompt for select cmd
$*  all positional params                       $REPLY      return value of read cmd
$@  all positional params in an array           $GROUPS     all groups current user belongs to
$#  number of positional params                 $OPTARG     getopt last option value
$?  exit status                                 $OPTIND     getopt last option index
$-  current option flag                         $OPTERR     getopt error message
$$  PID of shell or shell script
$!  PID of most recent async cmd
$0  name of shell script.
$_  absolute pathname

Compound Commands
=================

Looping Constructs                               Conditional Constructus
------------------                               -----------------------

until ...; do ...; done                         if ...; then ...; [elif ...; then ...;] fi
while ...; do ...; done                         case ... in
for ...; do ...; done                                   ...) ...
for ... [in ...]; do ...; done                          ...) ...
for (( expr1; expr2; expr3 )); do ...; done     esac
                                                select ... [in ...]; do ...; done
Grouping Commands
-----------------

()      execute enclosed commands
        in a subshell
{}      execute enclosed commands
        in current shell. needs a ";"
        to terminate command.

References
----------
http://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html
http://www.gnu.org/software/bash/manual/html_node/Special-Parameters.html
http://www.gnu.org/software/bash/manual/html_node/Bash-Variables.html
http://www.gnu.org/software/bash/manual/html_node/Compound-Commands.html