Cómo cortar una matriz en Bash
Mirando la sección "Array" en la página man de bash(1), no encontré una manera de cortar un array.
Así que se me ocurrió esta función demasiado complicada:
#!/bin/bash
# @brief: slice a bash array
# @arg1: output-name
# @arg2: input-name
# @args: seq args
# ----------------------------------------------
function slice() {
local output=$1
local input=$2
shift 2
local indexes=$(seq $*)
local -i i
local tmp=$(for i in $indexes
do echo "$(eval echo \"\${$input[$i]}\")"
done)
local IFS=$'\n'
eval $output="( \$tmp )"
}
Usado así:
$ A=( foo bar "a b c" 42 )
$ slice B A 1 2
$ echo "${B[0]}" # bar
$ echo "${B[1]}" # a b c
¿Hay una mejor manera de hacer esto?
4 answers
Vea la sección Expansión de parámetros en la página Bash man
. A[@]
devuelve el contenido de la matriz, :1:2
toma una porción de longitud 2, comenzando en el índice 1.
A=( foo bar "a b c" 42 )
B=("${A[@]:1:2}")
C=("${A[@]:1}") # slice to the end of the array
echo "${B[@]}" # bar a b c
echo "${B[1]}" # a b c
echo "${C[@]}" # bar a b c 42
echo "${C[@]: -2:2}" # a b c 42 # The space before the - is necesssary
Tenga en cuenta que el hecho de que "a b c" es un elemento de matriz (y que contiene un espacio adicional) se conserva.
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2018-07-24 16:35:30
También hay un atajo conveniente para obtener todos los elementos de la matriz a partir del índice especificado. Por ejemplo "{{A [@]: 1}" sería la "cola" del array, es decir, el array sin su primer elemento.
version=4.7.1
A=( ${version//\./ } )
echo "${A[@]}" # 4 7 1
B=( "${A[@]:1}" )
echo "${B[@]}" # 7 1
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2013-05-29 20:42:53
Array slicing como en Python (De la biblioteca rebash):
array_slice() {
local __doc__='
Returns a slice of an array (similar to Python).
From the Python documentation:
One way to remember how slices work is to think of the indices as pointing
between elements, with the left edge of the first character numbered 0.
Then the right edge of the last element of an array of length n has
index n, for example:
```
+---+---+---+---+---+---+
| 0 | 1 | 2 | 3 | 4 | 5 |
+---+---+---+---+---+---+
0 1 2 3 4 5 6
-6 -5 -4 -3 -2 -1
```
>>> local a=(0 1 2 3 4 5)
>>> echo $(array.slice 1:-2 "${a[@]}")
1 2 3
>>> local a=(0 1 2 3 4 5)
>>> echo $(array.slice 0:1 "${a[@]}")
0
>>> local a=(0 1 2 3 4 5)
>>> [ -z "$(array.slice 1:1 "${a[@]}")" ] && echo empty
empty
>>> local a=(0 1 2 3 4 5)
>>> [ -z "$(array.slice 2:1 "${a[@]}")" ] && echo empty
empty
>>> local a=(0 1 2 3 4 5)
>>> [ -z "$(array.slice -2:-3 "${a[@]}")" ] && echo empty
empty
>>> [ -z "$(array.slice -2:-2 "${a[@]}")" ] && echo empty
empty
Slice indices have useful defaults; an omitted first index defaults to
zero, an omitted second index defaults to the size of the string being
sliced.
>>> local a=(0 1 2 3 4 5)
>>> # from the beginning to position 2 (excluded)
>>> echo $(array.slice 0:2 "${a[@]}")
>>> echo $(array.slice :2 "${a[@]}")
0 1
0 1
>>> local a=(0 1 2 3 4 5)
>>> # from position 3 (included) to the end
>>> echo $(array.slice 3:"${#a[@]}" "${a[@]}")
>>> echo $(array.slice 3: "${a[@]}")
3 4 5
3 4 5
>>> local a=(0 1 2 3 4 5)
>>> # from the second-last (included) to the end
>>> echo $(array.slice -2:"${#a[@]}" "${a[@]}")
>>> echo $(array.slice -2: "${a[@]}")
4 5
4 5
>>> local a=(0 1 2 3 4 5)
>>> echo $(array.slice -4:-2 "${a[@]}")
2 3
If no range is given, it works like normal array indices.
>>> local a=(0 1 2 3 4 5)
>>> echo $(array.slice -1 "${a[@]}")
5
>>> local a=(0 1 2 3 4 5)
>>> echo $(array.slice -2 "${a[@]}")
4
>>> local a=(0 1 2 3 4 5)
>>> echo $(array.slice 0 "${a[@]}")
0
>>> local a=(0 1 2 3 4 5)
>>> echo $(array.slice 1 "${a[@]}")
1
>>> local a=(0 1 2 3 4 5)
>>> array.slice 6 "${a[@]}"; echo $?
1
>>> local a=(0 1 2 3 4 5)
>>> array.slice -7 "${a[@]}"; echo $?
1
'
local start end array_length length
if [[ $1 == *:* ]]; then
IFS=":"; read -r start end <<<"$1"
shift
array_length="$#"
# defaults
[ -z "$end" ] && end=$array_length
[ -z "$start" ] && start=0
(( start < 0 )) && let "start=(( array_length + start ))"
(( end < 0 )) && let "end=(( array_length + end ))"
else
start="$1"
shift
array_length="$#"
(( start < 0 )) && let "start=(( array_length + start ))"
let "end=(( start + 1 ))"
fi
let "length=(( end - start ))"
(( start < 0 )) && return 1
# check bounds
(( length < 0 )) && return 1
(( start < 0 )) && return 1
(( start >= array_length )) && return 1
# parameters start with $1, so add 1 to $start
let "start=(( start + 1 ))"
echo "${@: $start:$length}"
}
alias array.slice="array_slice"
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2016-03-21 19:54:17
Digamos que estoy leyendo una matriz de usuario, luego quiero ver el elemento 3 al 7 ambos inclusive .
cnt=0
while read var;
do
myarr[cnt]=$var
cnt=$((cnt+1))
done
echo ${myarr[@]:3:5}
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2017-04-07 13:00:07