bash
[!NOTE|label:references:]
fancy bash
[!NOTE]
$ echo ${BASH_ALIASES[ls]}
ls --color=alwaysget bash login log ( for rc script debug )
$ bash -l -vrun with only one startup file ( for sharing accounts )
$ bash -i --rcfile="$HOME/.marslo/.imarslo"
array
[!NOTE|label:references:]
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 ${foo[@]} orange banana apple
sort array
[!NOTE|label:references:]
sample array:
declare -A authors declare -i i=0 for ((r = 0; r <= 255; r+=40)); do authors[$i]+="$r"; (( i++ )); done # output $ for k in "${!authors[@]}"; do echo "$k - ${authors["$k"]}"; done 6 - 240 5 - 200 4 - 160 3 - 120 2 - 80 1 - 40 0 - 0
sort array by key
[!TIP] !! highly recommend !!
$ for key in $(echo ${!authors[@]} | tr ' ' '\n' | sort -n); do echo $key - ${authors[$key]}; done 0 - 0 1 - 40 2 - 80 3 - 120 4 - 160 5 - 200 6 - 240$ printf "%s\n" "${!authors[@]}" | sort -n | while read -r key; do echo $key - ${authors[$key]}; done 0 - 0 1 - 40 2 - 80 3 - 120 4 - 160 5 - 200 6 - 240$ for k in "${!authors[@]}"; do echo "$k - ${authors["$k"]}"; done | sort -n 0 - 0 1 - 40 2 - 80 3 - 120 4 - 160 5 - 200 6 - 240or using IFS to sort key before loop
authors_indexes=( ${!authors[@]} ) oIFS="$IFS" IFS=$'\n' authors_sorted=( $( printf '%s\n' "${!authors[@]}" | sort ) ) IFS="$oIFS" for k in "${!authors_sorted[@]}"; do echo "$k - ${authors["$k"]}" done # result 0 - 0 1 - 40 2 - 80 3 - 120 4 - 160 5 - 200 6 - 240
Brace Expansion
echo a{d,c,b}e
Tilde Expansion
~
Shell Parameter Expansion
string=01234567890abc; echo ${string:7:2}
Command Substitution
$(command) or command
Arithmetic Expansion
$(( expression ))
Process Substitution
<(list) or >(list)
Word Splitting
$IFS
Filename Expansion
*, ? , [..],...
IFS
[!NOTE]
# 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 - bazor
$ cat -c -etv <<<"$IFS" ^I$ $ $ printf "%s" "$IFS" | od -to1 -vtc 0000000 040 011 012 \t \n 0000003example
$ 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
while read show variable
# due to 7 fields are spitted via `:` in /etc/passwd
IFS=':' read f1 f2 f3 f4 f5 f6 f7 < /etc/passwdBash scans each word for the characters
'*','?', and'[', unless the-f(set -f) option has been set
match found && nullglob disabled
the word is regarded as a pattern
no match found && nullglob disabled
the word is left unchanged
no match found && nullglob set
the word is removed
no match found && failglob set
show error msg and cmd won't be exectued
nocaseglob enabled
patten match case insensitive
set -o noglob or set -f
* will not be expanded
shopt -s dotglob
* will including all .*. see zip package with dot-file
1
"$a"
apple
variables are expanded inside ""
2
'$a'
$a
variables are not expanded inside ''
3
"'$a'"
'apple'
'' has no special meaning inside ""
4
'"$a"'
"$a"
"" is treated literally inside ''
5
'\''
invalid
can not escape a ' within ''; use "'" or $'\'' (ANSI-C quoting)
6
"red$arocks"
red
$arocks does not expand $a; use ${a}rocks to preserve $a
7
"redapple$"
redapple$
$ followed by no variable name evaluates to $
8
'\"'
\"
\ has no special meaning inside ''
9
"\'"
\'
\' is interpreted inside "" but has no significance for '
10
"\""
"
\" is interpreted inside ""
11
"*"
*
glob does not work inside "" or ''
12
"\t\n"
\t
and have no special meaning inside "" or ''; use ANSI-C quoting
13
"echo hi"
hi
`` and $() are evaluated inside "" (backquotes are retained in actual output)
14
'echo hi'
echo` hi
`` and $() are not evaluated inside '' (backquotes are retained in actual output)
15
'${arr[0]}'
${arr[0]}
array access not possible inside ''
16
"${arr[0]}"
apple
array access works inside ""
17
$'$a\''
$a'
single quotes can be escaped inside ANSI-C quoting
18
"$'\t'"
$'\t'
ANSI-C quoting is not interpreted inside ""
19
'!cmd'
!cmd
history expansion character '!' is ignored inside ''
20
"!cmd"
cmd args
expands to the most recent command matching "cmd"
21
$'!cmd'
!cmd
history expansion character '!' is ignored inside ANSI-C quotes
ternary arithmetic
[!NOTE]
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
# 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-10scp multipule folder/file to target server
$ scp -r $(echo dir{1..10}) user@target.server:/target/server/path/$ 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 100fast copy or moving or something (detials -> brace expansion)
example 1:
$ ls | grep foo $ touch foo{1,2,3} $ ls | grep foo foo1 foo2 foo3example 2
$ ls | grep foo $ touch foo-{a..d} $ ls | grep foo foo-a foo-b foo-c foo-dexample 3
$ ls foo-* foo-a foo-b foo-c foo-d $ mv foo-{a,} $ ls foo-* foo-a foo-b foo-c foo-dexample 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 file1pipe and stdin
to multiple variables
$ IFS=' ,' read -r x y z <<< "255, 100, 147"
$ echo "x - $x; y - $y; z - $z"
x - 255; y - 100; z - 147to array
$ IFS=' ,' read -r -a arr <<< "255, 100, 147" $ echo "0 - ${arr[0]}; 1 - ${arr[1]}; 2 - ${arr[2]}" 0 - 255; 1 - 100; 2 - 147every single char to array including spaces
[!TIP]
tricky of sed
$ echo "255, 100, 147" | sed $'s/./&\v/g' 2 5 5 , 1 0 0 , 1 4 7
$ IFS=$'\v' read -ra arr <<<"$(echo "255, 100, 147" | sed $'s/./&\v/g')" $ for k in "${!arr[@]}"; do echo "$k -- ${arr[$k]}"; done 0 -- 2 1 -- 5 2 -- 5 3 -- , 4 -- 5 -- 1 6 -- 0 7 -- 0 8 -- , 9 -- 10 -- 1 11 -- 4 12 -- 7 # or using printf $ for k in "${!arr[@]}"; do printf "%02s - %s;\n" "$k" "${arr[$k]}"; done 00 - 2; 01 - 5; 02 - 5; 03 - ,; 04 - ; 05 - 1; 06 - 0; 07 - 0; 08 - ,; 09 - ; 10 - 1; 11 - 4; 12 - 7;
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 ( for command | trim )
read -r var ( for command | trim )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
another trim solution for leading and trailing spaces
trim() { local var="$*" var="${var#"${var%%[![:space:]]*}"}" # remove leading whitespace characters var="${var%"${var##*[![:space:]]}"}" # remove trailing whitespace characters printf '%s' "$var" }
!
start a history substitution
!n
refer to command line n
!-n
refer to the command n lines back
!!
refer to the previous command
!string
refer to the most recent command preceding the current position in the history list starting with string
!?string[?]
refer to the most recent command preceding the current position in the history list containing string.
^string1^string2^
!!:s^string1^string2^
quick substitution. repeat the last command, replacing string1 with string2
!#
the entire command line typed so far
!!
designates the preceding command
!!:$ or !$
designates the last argument of the preceding command
!fi:2
designates the second argument of the most recent command starting with the letters fi
~
$HOME
~/foo: $HOME/foo
~+
$PWD
~+/foo: $PWD/foo
~N
dirs +N
-
~+N
dirs +N
-
~-N
dirs -N
-
# 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 $(dirs -3)
~/a/b/c/d$*
expands to the positional parameters, starting from one. when the expansion occurs within double quotes, it expands to a single word with the value of each parameter separated by the first character of the ifs special variable.
$@
expands to the positional parameters, starting from one. when the expansion occurs within double quotes, each parameter expands to a separate word.
$#
expands to the number of positional parameters in decimal.
$?
expands to the exit status of the most recently executed foreground pipeline.
$-
a hyphen expands to the current option flags as specified upon invocation, by the set built-in command, or those set by the shell itself (such as the -i).
$$
expands to the process id of the shell.
$!
expands to the process id of the most recently executed background (asynchronous) command.
$0
expands to the name of the shell or shell script.
$_
the underscore variable is set at shell startup and contains the absolute file name of the shell or script being executed as passed in the argument list. subsequently, it expands to the last argument to the previous command, after expansion. it is also set to the full pathname of each command executed and placed in the environment exported to that command. when checking mail, this parameter holds the name of the mail file.
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