Advanced Bash Usage Cheat Sheet

These commands were taking from the talk Introduction to Advanced Bash Usage by James Pannacciulli

Updated 21 Jan 2017 06:54:53

Getting help

type
help
apropos
man
info

Definitions

word: sequence of characters
list: sequence of one or more commands or pipelines
name: a word that has only alphanumeric characters
parameter: entity that stores values.

Compound Commands

Iteration
- while
- until
- for
- select
Conditionals
- if
- case
Command Groups
- (list) {list; })

While and Until Loops

while **list1**; do **list2**; done

until **list1**; do **list2**; done

For and Select Loops

for name in words; do list; done

	for w in w1 w2 "w3 w3-2"; do echo $w; done

for (( expr1 ; expr2 ; expr3 )); do list; done

	for (( i = 0 ; i < 5 ; i++ )) ; do echo $ioo ; done

select name in words; do list; done

	select choice in one two "three four"; do echo "$REPLY : $choice"; done

Tests

https://youtu.be/uqHjc7hlqd0?t=11m56s

Conditional Expressions

[ *expression* ] or test *expression*

[[ expression ]]

word splitting is not performed
right side of string comparisons (==, !=) treated as
- pattern when not quoted
- string when quoted

Not Empty: [[ -n string ]]

String is Empty: [[ -z string ]]

String and String2 are the Same: [[ string == string2 ]]

String and String2 are not the same: [[ string != string2 ]]

String matches regular expression [[ string =~ regex ]]

File Exists: [[-e file ]]

File is a regular file: [[ -d file ]]

File is a directory: [[ -d file ]]

fd is open and refers to a terminal: [[ -t fd ]]

If Then Else

https://youtu.be/uqHjc7hlqd0?t=14m23s

Pattern Matching

https://youtu.be/uqHjc7hlqd0?t=15m3s

Pattern matching is used in bash for [[ ]] and case keywords, pathname expansion, and some types of parameter expansion.

* Matches any string, including null.
? Matches any single character.
[character class]Matches any of the characters enclosed between []
- [^..] Matches any character not in the class
- [x-z] Matches the range of characters from x to z
- [[:class:]] Matches according to the POSIX classes:
  - alnum
  - alpha
  - ascii
  - blank
  - cntrl
  - digit
  - graph
  - lower
  - print
  - punct
  - space

Conditionals: Case

https://youtu.be/uqHjc7hlqd0?t=15m49s

Comand Groups

https://youtu.be/uqHjc7hlqd0?t=16m59s

Redirection

https://youtu.be/uqHjc7hlqd0?t=21m36s

Command and Process Substitution

https://youtu.be/uqHjc7hlqd0?t=22m20s

Parameters

https://youtu.be/uqHjc7hlqd0?t=23m9s

###Positional Parameters ###Special Parameters ###Variables

Parameter Expansion

###Conditionals https://youtu.be/uqHjc7hlqd0?t=24m5s

###Substrings https://youtu.be/uqHjc7hlqd0?t=26m57s

###Indirection, Listing, Length https://youtu.be/uqHjc7hlqd0?t=29m1s

###Pattern Substitution

https://youtu.be/uqHjc7hlqd0?t=30m17s

param=racecar
echo ${param/c?/T}
raTcar

Left Edge

param="04: dash"
echo ${param/#* /}
dash

Right Edge

param=racecar
echo ${param/%r/t}
racecat

Indexed Arrays

Not Available in POSIX Shell https://youtu.be/uqHjc7hlqd0?t=31m3s

Arithmetic Expansion

https://youtu.be/uqHjc7hlqd0?t=33m47s

##Brace Expansion https://youtu.be/uqHjc7hlqd0?t=35m26s

$ echo he{ll,lp}
hell help

$ echo ki{ss,ll}ing
kissing killing

$ echo bash{,e{d,s},ful{,ly,ness},ing}
bash bashed bashes bashful bashfully bashfulness bashing

$ echo foo{,}
foo foo

$ echo {a..z}
a b c d e f g h i j k l m n o p q r s t u v w x y z

$ echo {1..2}
1 2

$ echo {1..1}
1

$ echo {1..0}
1 0

$ echo {9..0..2}
9 7 5 3 1

##Functions https://youtu.be/uqHjc7hlqd0?t=37m49s

##Session Portability https://youtu.be/uqHjc7hlqd0?t=40m35s

moiz-frost/Advanced Bash Usage CheatSheet.md