• fancy bash
• alias
  • bash -<parameter>
• shell expansions
  • IFS
  • word splitting
  • filename expansion
• quoting
• ternary arithmetic
• brace expansion
  • segmented continuous
  • scp multipule folder/file to target server
  • all about {curly braces} in bash
  • fast copy or moving or something (detials -> brace expansion)
  • multiple directories creation
  • copy single file to multipule folders
• pipe and stdin
  • read stdin from pipe
  • read -r var
• event designators
  • word designators
• tilde expansion
• special parameters

[!NOTE] references:

• Bash scripting cheatsheet
• Introduction to Bash Array

• Bash For Loop Array: Iterate Through Array Values

  $ declare -A foo=(
                     ["one"]="apple"
                     ["two"]="orange"
                     ["three"]="banana"
                   )
  
  # show keys
  $ echo ${!foo[@]}
  two three one
  
  # show values
  $ echo ${foo[@]}
  orange banana apple
  

fancy bash

[!NOTE]

• ohmybash/oh-my-bash
• Bash-it/bash-it
• akinomyoga/ble.sh

alias

$ echo ${BASH_ALIASES[ls]}
ls --color=always

bash -<parameter>

• get bash login log ( for rc script debug )

  $ bash -l -v
  

• run with only one startup file ( for sharing accounts )

  $ bash -i --rcfile="$HOME/.marslo/.imarslo"
  

shell expansions

IFS

[!NOTE]

• bash read command splits line into words using space as delimiter even though space is not in IFS
• Bash/KSH: Define Delimiter (IFS) While Using read Command

# default IFS
$ echo "${IFS@Q}"
$' \t\n'

$ echo "$IFS" | od -tcx1
0000000      \t  \n  \n
         20  09  0a  0a
0000004

$ echo -n "$IFS" | od -tcx1
0000000      \t  \n
         20  09  0a
0000003

# i.e.:
$ read a b c <<< "foo bar baz"; echo $a - $b - $c
foo - bar - baz

• or

  $ cat -c -etv <<<"$IFS"
   ^I$
  $
  
  $ printf "%s" "$IFS" | od -to1 -vtc
  0000000 040 011 012
               \t  \n
  0000003
  

• example

  $ IFS=' ' read -p 'Enter your first and last name : ' first last; echo ">> hello $first $last"
  Enter your first and last name : marslo jiao
  >> hello marslo jiao
  
  # read from array
  $ foo=( x=y a=b )
  $ while IFS='=' read -r var value; do echo "$var >> $value"; done < <(printf '%s\n' "${foo[@]}")
  x >> y
  a >> b
  

  

word splitting

# due to 7 fields are spitted via `:` in /etc/passwd
IFS=':' read f1 f2 f3 f4 f5 f6 f7 < /etc/passwd

filename expansion

Bash scans each word for the characters '*', '?', and '[', unless the -f (set -f) option has been set

quoting

• Difference between single and double quotes in Bash
• ANSI-C quoting with $'' - GNU Bash Manual
• Locale translation with $"" - GNU Bash Manual
• A three-point formula for quotes

a=apple      # a simple variable
arr=(apple)  # an indexed array with a single element

ternary arithmetic

[!NOTE]

• Shell Scripting Ternary operator to get string result

• string

  $ [[ '.' = '.' ]] && path='.' || path='--'
  $ echo $path
  .
  
  $ [[ '.' = '-' ]] && path='.' || path='--'
  $ echo $path
  --
  

• mathematical operation

  $ (( 3 == 3 ? (var=1) : (var=0) ))
  $ echo $var
  1
  
  $ (( 3 == 1 ? (var=1) : (var=0) ))
  $ echo $var
  0
  

brace expansion

segmented continuous

# exclude 7 from 1-10
$ echo test-{{1..6},{8..10}}
test-1 test-2 test-3 test-4 test-5 test-6 test-8 test-9 test-10

scp multipule folder/file to target server

$ scp -r $(echo dir{1..10}) user@target.server:/target/server/path/

all about {curly braces} in bash

$ echo 00{1..9} 0{10..99} 100
001 002 003 004 005 006 007 008 009 010 011 012 013 014 015 016 017 018 019 020 021 022 023 024 025 026 027 028 029 030 031 032 033 034 035 036 037 038 039 040 041 042 043 044 045 046 047 048 049 050 051 052 053 054 055 056 057 058 059 060 061 062 063 064 065 066 067 068 069 070 071 072 073 074 075 076 077 078 079 080 081 082 083 084 085 086 087 088 089 090 091 092 093 094 095 096 097 098 099 100

$ dec2bin=({0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1})
$ echo ${dec2bin[1]}
00000001
$ echo ${dec2bin[0]}
00000000
$ echo ${dec2bin[255]}
11111111

$ month=("Jan" "Feb" "Mar" "Apr" "May" "Jun" "Jul" "Aug" "Sep" "Oct" "Nov" "Dec")
$ echo ${month[5]}
Jun

$ echo {10..0..2}
10 8 6 4 2 0
$ echo {1..100..3}
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 100

fast copy or moving or something (detials -> brace expansion)

• Example 1:

  $ ls | grep foo
  $ touch foo{1,2,3}
  $ ls | grep foo
  foo1
  foo2
  foo3
  

• Example 2

  $ ls | grep foo
  $ touch foo-{a..d}
  $ ls | grep foo
  foo-a
  foo-b
  foo-c
  foo-d
  

• Example 3

  $ ls foo-*
  foo-a  foo-b  foo-c  foo-d
  $ mv foo-{a,}
  $ ls foo-*
  foo-  foo-b  foo-c  foo-d
  

• Example 4

  $ mkdir -p test/{a,b,c,d}
  $ tree test/
  test/
  ├── a
  ├── b
  ├── c
  └── d
  
  4 directories, 0 files
  

multiple directories creation

$ mkdir sa{1..50}
$ mkdir -p sa{1..50}/sax{1..50}
$ mkdir {a-z}12345
$ mkdir {1,2,3}
$ mkdir test{01..10}
$ mkdir -p `date '+%y%m%d'`/{1,2,3}
$ mkdir -p $USER/{1,2,3}

copy single file to multipule folders

$ echo dir1 dir2 dir3 | xargs -n 1 cp file1

# or
$ echo dir{1..10} | xargs -n 1 cp file1

pipe and stdin

read stdin from pipe

[!TIP]

# with IFS
$ echo '   hello  world   ' | { IFS='' read msg; echo "${msg}"; } | tr ' ' '.'
...hello..world...
$ echo '   hello  world   ' | { IFS='' read msg; echo "${msg}" | sed -e 's/^[[:blank:]]*//;s/[[:blank:]]*$//'; } | tr ' ' '.'
hello..world

# without IFS
$ echo '   hello  world   ' | { read msg; echo "${msg}"; } | tr ' ' '.'
hello..world

read -r var

• script as command line

  $ cat trim.sh
  #!/usr/bin/env bash
  
  trim() {
    echo "$@" | sed -e 's/^[[:blank:]]*//;s/[[:blank:]]*$//'
  }
  
  IFS='' read -r myvar
  trim "${myvar}"
  

  • result

    $ IFS=''
    $ s='   aa  bb   '
    $ echo "${s}" | tr ' ' '.'                                              # ...aa..bb...
    $ echo "${s}" | ./trim.sh | tr ' ' '.'                                  # aa..bb
    $ echo " a | b | c " | awk -F'|' '{print $2}' | tr ' ' '.'              # .b.
    $ echo " a | b | c " | awk -F'|' '{print $2}' | ./trim.sh | tr ' ' '.'  # b
    

• running inside the script

  $ cat example.sh
  #!/usr/bin/env bash
  
  trim() {
    IFS='' read -r str
    echo "${str}" | sed -e 's/^[[:blank:]]*//;s/[[:blank:]]*$//'
  }
  
  s='   aa  bb   '
  echo "${s}" | tr ' ' '.'
  echo "${s}" | trim | tr ' ' '.'
  

  • result

    $ ./example.sh
    ...aa..bb...
    aa..bb
    

event designators

word designators

tilde expansion

# prepare
$ mkdir -p a/b/c/d
$ cd a && pushd .
$ cd b && pushd .
$ cd c && pushd .
$ cd d && pushd .

# result
$ dirs -v
 0  ~/a/b/c/d
 1  ~/a/b/c/d
 2  ~/a/b/c
 3  ~/a/b
 4  ~/a

$ echo $(dirs -1)
~/a/b
$ echo $(dirs -2)
~/a/b/c
$ echo $(dirs -3)
~/a/b/c/d

special parameters