Let's say we declared two associative arrays:
#!/bin/bash
declare -A first
declare -A second
first=([ele]=value [elem]=valuee [element]=valueee)
second=([ele]=foo [elem]=fooo [element]=foooo)
# echo ${$1[$2]}
I want to echo the given hashmap and element from script inputs. For example, if I run sh.sh second elem, the script should echo fooo.
An inelegant but bullet-proof solution would be to white-list $1 with the allowed values:
#!/bin/bash
# ...
[[ $2 ]] || exit 1
unset result
case $1 in
first) [[ ${first["$2"]+X} ]] && result=${first["$2"]} ;;
second) [[ ${second["$2"]+X} ]] && result=${second["$2"]} ;;
*) exit 1 ;;
esac
[[ ${result+X} ]] && printf '%s\n' "$result"
notes:
[[ $2 ]] || exit 1 because bash doesn't allow empty keys
[[ ${var+X} ]] checks that the variable var is defined; with this expansion you can also check that an index or key is defined in an array.
A couple ideas come to mind:
Variable indirection expansion
Per this answer:
arr="$1[$2]" # build array reference from input fields
echo "${!arr}" # indirect reference via the ! character
For the sample call sh.sh second elem this generates:
fooo
Nameref (declare -n) (requires bash 4.3+)
declare -n arr="$1"
echo "${arr[$2]}"
For the sample call sh.sh second elem this generates:
fooo
I need to remove an element from an array in bash shell.
Generally I'd simply do:
array=("${(#)array:#<element to remove>}")
Unfortunately the element I want to remove is a variable so I can't use the previous command.
Down here an example:
array+=(pluto)
array+=(pippo)
delete=(pluto)
array( ${array[#]/$delete} ) -> but clearly doesn't work because of {}
Any idea?
The following works as you would like in bash and zsh:
$ array=(pluto pippo)
$ delete=pluto
$ echo ${array[#]/$delete}
pippo
$ array=( "${array[#]/$delete}" ) #Quotes when working with strings
If need to delete more than one element:
...
$ delete=(pluto pippo)
for del in ${delete[#]}
do
array=("${array[#]/$del}") #Quotes when working with strings
done
Caveat
This technique actually removes prefixes matching $delete from the elements, not necessarily whole elements.
Update
To really remove an exact item, you need to walk through the array, comparing the target to each element, and using unset to delete an exact match.
array=(pluto pippo bob)
delete=(pippo)
for target in "${delete[#]}"; do
for i in "${!array[#]}"; do
if [[ ${array[i]} = $target ]]; then
unset 'array[i]'
fi
done
done
Note that if you do this, and one or more elements is removed, the indices will no longer be a continuous sequence of integers.
$ declare -p array
declare -a array=([0]="pluto" [2]="bob")
The simple fact is, arrays were not designed for use as mutable data structures. They are primarily used for storing lists of items in a single variable without needing to waste a character as a delimiter (e.g., to store a list of strings which can contain whitespace).
If gaps are a problem, then you need to rebuild the array to fill the gaps:
for i in "${!array[#]}"; do
new_array+=( "${array[i]}" )
done
array=("${new_array[#]}")
unset new_array
You could build up a new array without the undesired element, then assign it back to the old array. This works in bash:
array=(pluto pippo)
new_array=()
for value in "${array[#]}"
do
[[ $value != pluto ]] && new_array+=($value)
done
array=("${new_array[#]}")
unset new_array
This yields:
echo "${array[#]}"
pippo
This is the most direct way to unset a value if you know it's position.
$ array=(one two three)
$ echo ${#array[#]}
3
$ unset 'array[1]'
$ echo ${array[#]}
one three
$ echo ${#array[#]}
2
This answer is specific to the case of deleting multiple values from large arrays, where performance is important.
The most voted solutions are (1) pattern substitution on an array, or (2) iterating over the array elements. The first is fast, but can only deal with elements that have distinct prefix, the second has O(n*k), n=array size, k=elements to remove. Associative array are relative new feature, and might not have been common when the question was originally posted.
For the exact match case, with large n and k, possible to improve performance from O(nk) to O(n+klog(k)). In practice, O(n) assuming k much lower than n. Most of the speed up is based on using associative array to identify items to be removed.
Performance (n-array size, k-values to delete). Performance measure seconds of user time
N K New(seconds) Current(seconds) Speedup
1000 10 0.005 0.033 6X
10000 10 0.070 0.348 5X
10000 20 0.070 0.656 9X
10000 1 0.043 0.050 -7%
As expected, the current solution is linear to N*K, and the fast solution is practically linear to K, with much lower constant. The fast solution is slightly slower vs the current solution when k=1, due to additional setup.
The 'Fast' solution: array=list of input, delete=list of values to remove.
declare -A delk
for del in "${delete[#]}" ; do delk[$del]=1 ; done
# Tag items to remove, based on
for k in "${!array[#]}" ; do
[ "${delk[${array[$k]}]-}" ] && unset 'array[k]'
done
# Compaction
array=("${array[#]}")
Benchmarked against current solution, from the most-voted answer.
for target in "${delete[#]}"; do
for i in "${!array[#]}"; do
if [[ ${array[i]} = $target ]]; then
unset 'array[i]'
fi
done
done
array=("${array[#]}")
Here's a one-line solution with mapfile:
$ mapfile -d $'\0' -t arr < <(printf '%s\0' "${arr[#]}" | grep -Pzv "<regexp>")
Example:
$ arr=("Adam" "Bob" "Claire"$'\n'"Smith" "David" "Eve" "Fred")
$ echo "Size: ${#arr[*]} Contents: ${arr[*]}"
Size: 6 Contents: Adam Bob Claire
Smith David Eve Fred
$ mapfile -d $'\0' -t arr < <(printf '%s\0' "${arr[#]}" | grep -Pzv "^Claire\nSmith$")
$ echo "Size: ${#arr[*]} Contents: ${arr[*]}"
Size: 5 Contents: Adam Bob David Eve Fred
This method allows for great flexibility by modifying/exchanging the grep command and doesn't leave any empty strings in the array.
Partial answer only
To delete the first item in the array
unset 'array[0]'
To delete the last item in the array
unset 'array[-1]'
To expand on the above answers, the following can be used to remove multiple elements from an array, without partial matching:
ARRAY=(one two onetwo three four threefour "one six")
TO_REMOVE=(one four)
TEMP_ARRAY=()
for pkg in "${ARRAY[#]}"; do
for remove in "${TO_REMOVE[#]}"; do
KEEP=true
if [[ ${pkg} == ${remove} ]]; then
KEEP=false
break
fi
done
if ${KEEP}; then
TEMP_ARRAY+=(${pkg})
fi
done
ARRAY=("${TEMP_ARRAY[#]}")
unset TEMP_ARRAY
This will result in an array containing:
(two onetwo three threefour "one six")
Here's a (probably very bash-specific) little function involving bash variable indirection and unset; it's a general solution that does not involve text substitution or discarding empty elements and has no problems with quoting/whitespace etc.
delete_ary_elmt() {
local word=$1 # the element to search for & delete
local aryref="$2[#]" # a necessary step since '${!$2[#]}' is a syntax error
local arycopy=("${!aryref}") # create a copy of the input array
local status=1
for (( i = ${#arycopy[#]} - 1; i >= 0; i-- )); do # iterate over indices backwards
elmt=${arycopy[$i]}
[[ $elmt == $word ]] && unset "$2[$i]" && status=0 # unset matching elmts in orig. ary
done
return $status # return 0 if something was deleted; 1 if not
}
array=(a 0 0 b 0 0 0 c 0 d e 0 0 0)
delete_ary_elmt 0 array
for e in "${array[#]}"; do
echo "$e"
done
# prints "a" "b" "c" "d" in lines
Use it like delete_ary_elmt ELEMENT ARRAYNAME without any $ sigil. Switch the == $word for == $word* for prefix matches; use ${elmt,,} == ${word,,} for case-insensitive matches; etc., whatever bash [[ supports.
It works by determining the indices of the input array and iterating over them backwards (so deleting elements doesn't screw up iteration order). To get the indices you need to access the input array by name, which can be done via bash variable indirection x=1; varname=x; echo ${!varname} # prints "1".
You can't access arrays by name like aryname=a; echo "${$aryname[#]}, this gives you an error. You can't do aryname=a; echo "${!aryname[#]}", this gives you the indices of the variable aryname (although it is not an array). What DOES work is aryref="a[#]"; echo "${!aryref}", which will print the elements of the array a, preserving shell-word quoting and whitespace exactly like echo "${a[#]}". But this only works for printing the elements of an array, not for printing its length or indices (aryref="!a[#]" or aryref="#a[#]" or "${!!aryref}" or "${#!aryref}", they all fail).
So I copy the original array by its name via bash indirection and get the indices from the copy. To iterate over the indices in reverse I use a C-style for loop. I could also do it by accessing the indices via ${!arycopy[#]} and reversing them with tac, which is a cat that turns around the input line order.
A function solution without variable indirection would probably have to involve eval, which may or may not be safe to use in that situation (I can't tell).
Using unset
To remove an element at particular index, we can use unset and then do copy to another array. Only just unset is not required in this case. Because unset does not remove the element it just sets null string to the particular index in array.
declare -a arr=('aa' 'bb' 'cc' 'dd' 'ee')
unset 'arr[1]'
declare -a arr2=()
i=0
for element in "${arr[#]}"
do
arr2[$i]=$element
((++i))
done
echo "${arr[#]}"
echo "1st val is ${arr[1]}, 2nd val is ${arr[2]}"
echo "${arr2[#]}"
echo "1st val is ${arr2[1]}, 2nd val is ${arr2[2]}"
Output is
aa cc dd ee
1st val is , 2nd val is cc
aa cc dd ee
1st val is cc, 2nd val is dd
Using :<idx>
We can remove some set of elements using :<idx> also. For example if we want to remove 1st element we can use :1 as mentioned below.
declare -a arr=('aa' 'bb' 'cc' 'dd' 'ee')
arr2=("${arr[#]:1}")
echo "${arr2[#]}"
echo "1st val is ${arr2[1]}, 2nd val is ${arr2[2]}"
Output is
bb cc dd ee
1st val is cc, 2nd val is dd
http://wiki.bash-hackers.org/syntax/pe#substring_removal
${PARAMETER#PATTERN} # remove from beginning
${PARAMETER##PATTERN} # remove from the beginning, greedy match
${PARAMETER%PATTERN} # remove from the end
${PARAMETER%%PATTERN} # remove from the end, greedy match
In order to do a full remove element, you have to do an unset command with an if statement. If you don't care about removing prefixes from other variables or about supporting whitespace in the array, then you can just drop the quotes and forget about for loops.
See example below for a few different ways to clean up an array.
options=("foo" "bar" "foo" "foobar" "foo bar" "bars" "bar")
# remove bar from the start of each element
options=("${options[#]/#"bar"}")
# options=("foo" "" "foo" "foobar" "foo bar" "s" "")
# remove the complete string "foo" in a for loop
count=${#options[#]}
for ((i = 0; i < count; i++)); do
if [ "${options[i]}" = "foo" ] ; then
unset 'options[i]'
fi
done
# options=( "" "foobar" "foo bar" "s" "")
# remove empty options
# note the count variable can't be recalculated easily on a sparse array
for ((i = 0; i < count; i++)); do
# echo "Element $i: '${options[i]}'"
if [ -z "${options[i]}" ] ; then
unset 'options[i]'
fi
done
# options=("foobar" "foo bar" "s")
# list them with select
echo "Choose an option:"
PS3='Option? '
select i in "${options[#]}" Quit
do
case $i in
Quit) break ;;
*) echo "You selected \"$i\"" ;;
esac
done
Output
Choose an option:
1) foobar
2) foo bar
3) s
4) Quit
Option?
Hope that helps.
There is also this syntax, e.g. if you want to delete the 2nd element :
array=("${array[#]:0:1}" "${array[#]:2}")
which is in fact the concatenation of 2 tabs. The first from the index 0 to the index 1 (exclusive) and the 2nd from the index 2 to the end.
POSIX shell script does not have arrays.
So most probably you are using a specific dialect such as bash, korn shells or zsh.
Therefore, your question as of now cannot be answered.
Maybe this works for you:
unset array[$delete]
What I do is:
array="$(echo $array | tr ' ' '\n' | sed "/itemtodelete/d")"
BAM, that item is removed.
This is a quick-and-dirty solution that will work in simple cases but will break if (a) there are regex special characters in $delete, or (b) there are any spaces at all in any items. Starting with:
array+=(pluto)
array+=(pippo)
delete=(pluto)
Delete all entries exactly matching $delete:
array=(`echo $array | fmt -1 | grep -v "^${delete}$" | fmt -999999`)
resulting in
echo $array -> pippo, and making sure it's an array:
echo $array[1] -> pippo
fmt is a little obscure: fmt -1 wraps at the first column (to put each item on its own line. That's where the problem arises with items in spaces.) fmt -999999 unwraps it back to one line, putting back the spaces between items. There are other ways to do that, such as xargs.
Addendum: If you want to delete just the first match, use sed, as described here:
array=(`echo $array | fmt -1 | sed "0,/^${delete}$/{//d;}" | fmt -999999`)
Actually, I just noticed that the shell syntax somewhat has a behavior built-in that allows for easy reconstruction of the array when, as posed in the question, an item should be removed.
# let's set up an array of items to consume:
x=()
for (( i=0; i<10; i++ )); do
x+=("$i")
done
# here, we consume that array:
while (( ${#x[#]} )); do
i=$(( $RANDOM % ${#x[#]} ))
echo "${x[i]} / ${x[#]}"
x=("${x[#]:0:i}" "${x[#]:i+1}")
done
Notice how we constructed the array using bash's x+=() syntax?
You could actually add more than one item with that, the content of a whole other array at once.
In ZSH this is dead easy (note this uses more bash compatible syntax than necessary where possible for ease of understanding):
# I always include an edge case to make sure each element
# is not being word split.
start=(one two three 'four 4' five)
work=(${(#)start})
idx=2
val=${work[idx]}
# How to remove a single element easily.
# Also works for associative arrays (at least in zsh)
work[$idx]=()
echo "Array size went down by one: "
[[ $#work -eq $(($#start - 1)) ]] && echo "OK"
echo "Array item "$val" is now gone: "
[[ -z ${work[(r)$val]} ]] && echo OK
echo "Array contents are as expected: "
wanted=("${start[#]:0:1}" "${start[#]:2}")
[[ "${(j.:.)wanted[#]}" == "${(j.:.)work[#]}" ]] && echo "OK"
echo "-- array contents: start --"
print -l -r -- "-- $#start elements" ${(#)start}
echo "-- array contents: work --"
print -l -r -- "-- $#work elements" "${work[#]}"
Results:
Array size went down by one:
OK
Array item two is now gone:
OK
Array contents are as expected:
OK
-- array contents: start --
-- 5 elements
one
two
three
four 4
five
-- array contents: work --
-- 4 elements
one
three
four 4
five
To avoid conflicts with array index using unset - see https://stackoverflow.com/a/49626928/3223785 and https://stackoverflow.com/a/47798640/3223785 for more information - reassign the array to itself: ARRAY_VAR=(${ARRAY_VAR[#]}).
#!/bin/bash
ARRAY_VAR=(0 1 2 3 4 5 6 7 8 9)
unset ARRAY_VAR[5]
unset ARRAY_VAR[4]
ARRAY_VAR=(${ARRAY_VAR[#]})
echo ${ARRAY_VAR[#]}
A_LENGTH=${#ARRAY_VAR[*]}
for (( i=0; i<=$(( $A_LENGTH -1 )); i++ )) ; do
echo ""
echo "INDEX - $i"
echo "VALUE - ${ARRAY_VAR[$i]}"
done
exit 0
[Ref.: https://tecadmin.net/working-with-array-bash-script/ ]
How about something like:
array=(one two three)
array_t=" ${array[#]} "
delete=one
array=(${array_t// $delete / })
unset array_t
#/bin/bash
echo "# define array with six elements"
arr=(zero one two three 'four 4' five)
echo "# unset by index: 0"
unset -v 'arr[0]'
for i in ${!arr[*]}; do echo "arr[$i]=${arr[$i]}"; done
arr_delete_by_content() { # value to delete
for i in ${!arr[*]}; do
[ "${arr[$i]}" = "$1" ] && unset -v 'arr[$i]'
done
}
echo "# unset in global variable where value: three"
arr_delete_by_content three
for i in ${!arr[*]}; do echo "arr[$i]=${arr[$i]}"; done
echo "# rearrange indices"
arr=( "${arr[#]}" )
for i in ${!arr[*]}; do echo "arr[$i]=${arr[$i]}"; done
delete_value() { # value arrayelements..., returns array decl.
local e val=$1; new=(); shift
for e in "${#}"; do [ "$val" != "$e" ] && new+=("$e"); done
declare -p new|sed 's,^[^=]*=,,'
}
echo "# new array without value: two"
declare -a arr="$(delete_value two "${arr[#]}")"
for i in ${!arr[*]}; do echo "arr[$i]=${arr[$i]}"; done
delete_values() { # arraydecl values..., returns array decl. (keeps indices)
declare -a arr="$1"; local i v; shift
for v in "${#}"; do
for i in ${!arr[*]}; do
[ "$v" = "${arr[$i]}" ] && unset -v 'arr[$i]'
done
done
declare -p arr|sed 's,^[^=]*=,,'
}
echo "# new array without values: one five (keep indices)"
declare -a arr="$(delete_values "$(declare -p arr|sed 's,^[^=]*=,,')" one five)"
for i in ${!arr[*]}; do echo "arr[$i]=${arr[$i]}"; done
# new array without multiple values and rearranged indices is left to the reader
I have a script that I'll be using in a system where the first three positional parameters are reserved, but I want to pass other parameters to the script to be used as variables. I can set default values for the variables, but if a parameter is included, I want that to take precedence. Here's a very basic script to illustrate:
#!/bin/bash
param1="$1"
param2="$2"
param3="$3"
param4="default4"
if [[ "$param4" == "" ]] && [[ "$4" == "" ]]; then
echo "A value was not specified for parameter 4. Script cannot execute. Exiting..."
exit 1
elif [[ "$4" != "" ]]; then
param4="$4"
else
echo "The built-in value for parameter 4 will be used in the script."
fi
echo "$param1"
echo "$param2"
echo "$param3"
echo "$param4"
If I run script a b c the output I get is:
The built-in value for parameter 4 will be used in the script.
a
b
c
default4
If I run script a b c d then the output is:
a
b
c
d
This is all well and good, but if I have 5-6 different parameters, I don't want to have to repeat the if..fi block that many times for each parameter.
So I've been trying to use a for loop to iterate through the parameters, but I haven't had much luck. The best attempt I came up with was:
#!/bin/bash
param1="$1"
param2="$2"
param3="$3"
param4="default4"
param5="default5"
param6="default6"
param7="default7"
defaultArray=( param4 param5 param6 param7 )
passedArray=( '$4' '$5' '$6' '$7' )
for (( i=0; i<${#defaultArray[#]}; i++ ));
do
if [[ "${defaultArray[$i]}" == "" ]] && [[ "${passedArray[$i]}" == "" ]]; then
echo "A value was not specified for parameter $((i+4)). Script cannot execute. Exiting..."
exit 1
elif [[ "${passedArray[$i]}" != "" ]]; then
eval "${defaultArray[$i]}"='"${passedArray[$i]}"'
else
echo "The built-in value for parameter $((i+4)) will be used in the script."
fi
done
echo "$param1"
echo "$param2"
echo "$param3"
echo "$param4"
echo "$param5"
echo "$param6"
echo "$param7"
But when I run this script a b c, or script a b c d, and whether or not I delete the default values in the script, I always get:
a
b
c
$4
$5
$6
$7
I think this because I needed to single-quote the positional parameter names in passedArray or else they just blank out, but then that hard-codes their names rather than the passed value.
Is there a way of doing this, or does trying to assign a positional parameter to a variable in an array and/or a for loop just not work? The thing I'm going to try next is a function, but I'm not sure that'd work any better...
Change
param4="default4"
if [[ "$param4" == "" ]] && [[ "$4" == "" ]]; then
echo "A value was not specified for parameter 4. Script cannot execute. Exiting..."
exit 1
elif [[ "$4" != "" ]]; then
param4="$4"
else
echo "The built-in value for parameter 4 will be used in the script."
fi
To:
if [[ ! -z $4 ]]; then
param4="$4"
else
param4="default4"
echo "The built-in value for parameter 4 will be used in the script."
fi
In your version of code, the first part of the if condition would never execute because param4 is already set just before if.
A more elegant and consiste way of doing this, given that you are using a default value for param4 anyway is:
param4=${4:-default4} # use default as "default4" unless $4 is set
For the second problem, your suspicion is right - single quotes won't expand the positional variables in the array assignment. So, change it to:
passedArray=( "$4" "$5" "$6" "$7" )
Your loops seems OK, except for this:
elif [[ "${passedArray[$i]}" != "" ]]; then
eval "${defaultArray[$i]}"='"${passedArray[$i]}"'
Why use eval here? You can say:
defaultArray[$i]=${passedArray[$i]}
Imagine I created an array like this:
IFS="|" read -ra ARR <<< "zero|one|||four"
now
echo ${#ARR[#]}
> 5
echo "${ARR[#]}"
> zero one four
echo "${ARR[0]}"
> zero
echo "${ARR[2]}"
> # Nothing, because it is empty
The question is how can I replace the empty elements with another string?
I have tried
${ARR[#]///other}
${ARR[#]//""/other}
none of them worked.
I want this as output:
zero one other other four
To have the shell expansion behave, you need to loop through its elements and perform the replacement on each one of them:
$ IFS="|" read -ra ARR <<< "zero|one|||four"
$ for i in "${ARR[#]}"; do echo "${i:-other}"; done
zero
one
other
other
four
Where:
${parameter:-word}
If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter is substituted.
To store them in a new array, just do so by appending with +=( element ):
$ new=()
$ for i in "${ARR[#]}"; do new+=("${i:-other}"); done
$ printf "%s\n" "${new[#]}"
zero
one
other
other
four
If you want to replace all empty values (actually modifying the list), you could do this :
for i in "${!ARR[#]}" ; do ARR[$i]="${ARR[$i]:-other}"; done
Which looks like this when indented (more readable I would say) :
for i in "${!ARR[#]}"
do
ARR[$i]="${ARR[$i]:-other}"
done
# Temporary array initialization
NEW=()
# Loop over the array, add only non-empty values to the new array
for i in "${ARR[#]}"; do
# Skip null items
if [ -z "$i" ]; then
continue
fi
# Add the rest of the elements to an array
NEW+=("${i}")
done
# Reinitialize your array
ARR=(${NEW[#]})
I want a script bash/sh/ksh which compare a lot of variables, maybe in an array, and tell me if variable is empty or not.
I think something like this, it but doesn't work.
ARRAY=(
bash="yes"
cash=""
trash="no"
empty=""
)
for var in "${ARRAY[#]}"; do
if [ "$var" == "$empty" ]
then
echo "$var is empty"
else
echo "$var is not empty"
fi
done
I want an output like this
bash is not empty
cash is empty...
If you're willing to limit your runtime environment to a recent version of bash (or modify the code to support ksh93's equivalent syntax),
#!/bin/bash
# ^^^^ -- specifically, bash 4.0 or newer
declare -A array # associative arrays need to be declared!
array=( [bash]="yes" [cash]="" [trash]="no" [empty]="" )
for idx in "${!array[#]}"; do
if [[ ${array[$idx]} ]]; then
echo "$idx is not empty"
else
echo "$idx is empty"
fi
done
To iterate over keys in an array, as opposed to values, the syntax is "${!array[#]}", as opposed to "${array[#]}"; if you merely iterate over the values, you don't know the name of the one currently being evaluated.
Alternately, let's say we aren't going to use an array at all; another way to set a namespace for variables you intend to be able to treat in a similar manner is by prefixing them:
#!/bin/bash
val_bash=yes
val_cash=
val_trash=no
val_empty=
for var in "${!val_#}"; do
if [[ ${!var} ]]; then
echo "${var#val_} is not empty"
else
echo "${var#val_} is empty"
fi
done
This works (on bash 3.x as well) because "${!prefix#}" expands to the list of variable names starting with prefix, and "${!varname}" expands to the contents of a variable whose name is itself stored in the variable varname.
Iterate over the array elements, and inside the loop for read set IFS as = to get variable and it's value in two separate variables, then check if the value is empty:
for i in "${array[#]}"; do
IFS== read var value <<<"$i"
if [ -z "$value" ]; then
echo "$var is empty"
else
echo "$var is not empty"
fi
done
Outputs:
bash is not empty
cash is empty
trash is not empty
empty is empty