I have an array with multiple lines, and I would like to select a specific line of the array in a for loop. And then use the data in the selected line for some analysis in the for loop.
ARRAY=(A1,A2
B1,B2
C1,C2)
When I applied the below code, I can assign "B1" to Trait1 and "B2" to Trait2. This works for j=1 or j=3 as well.
j=2
echo ${ARRAY[$j-1]}
Trait1="$(echo ${ARRAY[$j-1]} | cut -d',' -f1)"
Trait2="$(echo ${ARRAY[$j-1]} | cut -d',' -f2)"
echo $Trait1
echo $Trait2
Ultimately, I want to put the above code in a for loop. But this failed.
nLine=3
for j in $(eval echo "{1..$nLine}")
do
Trait1="$(echo ${ARRAY[$j-1]} | cut -d',' -f1)"
Trait2="$(echo ${ARRAY[$j-1]} | cut -d',' -f2)"
echo $Trait1
echo $Trait2
done
-bash: 1 2 3-1: syntax error in expression (error token is "2 3-1")
-bash: 1 2 3-1: syntax error in expression (error token is "2 3-1")
Thank you.
Keeping the current code design I'd probably want to use parameter expansion to break the array element into its 2 components ...
Data setup:
$ ARRAY=(A1,A2
B1,B2
C1,C2)
$ typeset -p ARRAY
declare -a ARRAY=([0]="A1,A2" [1]="B1,B2" [2]="C1,C2")
Quick demo of parameter expansion to break array element into parts:
$ x=${ARRAY[0]}
$ echo ${x}
A1,A2
$ echo ${x%,*}
A1
$ echo ${x#*,}
A2
Updating the PO's for loop to use parameter expansion, and replacing the eval/echo/j-1 with something a bit easier to read:
nLine=3
for (( j=0 ; j<nLine ; j++ ))
do
Trait1="${ARRAY[${j}]%,*}"
Trait2="${ARRAY[${j}]#*,}"
echo "${Trait1}"
echo "${Trait2}"
done
Generates the output:
A1
A2
B1
B2
C1
C2
The way you're using it, you should have a single string, not an array.
ARRAY='A1,A2
B1,B2
C1,C2'
Then when you use it as a here-string input to sed, it will receive multiple lines of input, and you can select the line you want with ${j}p.
As mentioned in the comments, this seems like a convoluted way to access array elements. You can simply use the shell's built-in array indexing operator.
Array assignments
ARRAY=(A1,A2
B1,B2
C1,C2)
and
ARRAY=(A1,A2 B1,B2 C1,C2)
are equivalent and both define an array with 3 elements: A1,A2, B1,B2, and C1,C2. Space(s), tab(s) and new-line(s) are used to separate array elements in compound assignments.
A for loop can be used to traverse an array:
# "${ARRAY[#]}" expands each element of ARRAY to a separate word
for elm in "${ARRAY[#]}"; do
# The value of the array element accessed is "$elm"
done
Or, using the alternate form of the for loop:
# ${#ARRAY[*]} expands to the number of elements in the ARRAY
for ((j = 0; j < ${#ARRAY[*]}; ++j)); do
# Array element can be referenced using ${ARRAY[j]}
done
assuming there is no gap between indices (bash allows an array with "holes").
Here strings, a variant of here documents, and read builtin with IFS variable can be used to parse the elements of the array:
IFS=, read Trait1 Trait2 <<< ${ARRAY[j]}
Here the IFS is used with the value , to cut the array element into Trait1 and Trait2 when there is a ,.
So, a sample program to demonstrate all of these may be:
#!/bin/bash
ARRAY=(A1,A2
B1,B2
C1,C2)
for elem in "${ARRAY[#]}"; do
IFS=, read Trait1 Trait2 <<< $elem
printf "%s\n%s\n" "$Trait1" "$Trait2"
done
or,
#!/bin/bash
ARRAY=(A1,A2
B1,B2
C1,C2)
for ((j = 0; j < ${#ARRAY[*]}; ++j)); do
IFS=, read Trait1 Trait2 <<< ${ARRAY[j]}
printf "%s\n%s\n" "$Trait1" "$Trait2"
done
I am trying to make an if statement where if array1 contains any of the strings in array2 it should print "match" else print "no match"
So far I have the following. Not sure how to complete it. Both loops should break as soon as the first match is found.
#!/bin/bash
array1=(a b c 1 2 3)
array2=(b 1)
for a in "${array1[#]}"
do
for b in "${array2[#]}"
do
if [ "$a" == "$b" ]; then
echo "Match!"
break
fi
done
done
Maybe this isn't even the best way to do it?
This illustrates the desired result
if [ array1 contains strings in array2 ]
then
echo "match"
else
echo "no match"
fi
To check whether array1 contains any entry from array2 you can use grep. This will be way faster and shorter than loops in bash.
The following commands exit with status code 0 if and only if there is a match. Use them as ...
if COMMAND FROM BELOW; then
echo match
else
echo no match
fi
Single-Line Array Entries
The simple version for strings without linebreaks is
printf %s\\n "${array1[#]}" | grep -qFxf <(printf %s\\n "${array2[#]}")
Multiline Array Entries
Sadly there doesn't seem to be a straightforward way to make this work for array entries with linebreaks. GNU grep has the option -z to set the "line" delimiters in the input to null, but apparently no option to do the same for the file provided to -f. Listing the entries from array2 as -e arguments to grep is not working either -- grep -F seems to be unable to match multiline patterns. However, we can use the following hack:
printf %q\\n "${array1[#]}" | grep -qFxf <(printf %q\\n "${array2[#]}")
Here we assume that bash's built-in printf %q always prints a unique single line -- which it currently does. However, future implementations of bash may change this. The documentation help printf only states that the output thas to be correctly quoted for bash.
For a fast solution, you're better off using an external tool that can process the entire array as a whole (such as the grep-based answers). Doing nested loops in pure bash is likely to be slower for any substantial amount of data (where the item-by-item processing in bash is likely to be more expensive than the external process start-up time).
However, if you do need a pure bash solution, I see that your current solution has no way to print out the "no match" scenario. In addition, it may print out "match" multiple times.
To fix that, you can just store the fact that a match has been found, and use that to both:
exit the outer loop early as well as the inner loop; and
print the correct string at the end.
To do this, you can use something like:
#!/bin/bash
# Test data.
array1=(a b c 1 2 3)
array2=(b 1)
# Default to not-found state.
foundMatch=false
for a in "${array1[#]}" ; do
for b in "${array2[#]}" ; do
# Any match switches to found state and exits inner loop.
[[ "$a" == "$b" ]] && foundMatch=true && break
done
# If found, exit outer loop as well.
${foundMatch} && break
done
# Output appropriate message for found/not-found state.
$foundMatch && echo "Match" || echo "No match"
For array elements which does not contain newlines, the grep -qf with printf "%s\n" would be a good option. For comparing arrays with any elements, I ended with this:
cmp -s /dev/null <(comm -z12 <(printf "%s\0" "${array1[#]}" | sort -z) <(printf "%s\0" "${array2[#]}" | sort -z))
The printf "%s\0" "${array[#]}" | sort -z print a sorted list of zero terminated array elements. The comm -z12 then extracts common elements in both lists. The cmp -s /dev/null checks if the output of comm is empty, which will not be empty if any element is in both lists. You could use [ -z "$(comm -z ...)" ] to check if the output of comm would be empty, but bash will complain that the output of a command captured with $(..) contains a null byte, so it's better to cmp -s /dev/null.
I think | is faster then <(), so your if could be:
if ! printf "%s\0" "${array1[#]}" | sort -z |
comm -z12 - <(printf "%s\0" "${array2[#]}" | sort -z) |
cmp -s /dev/null -; then
echo "Some elements are in both array1 and array2"
fi
The following could work:
printf "%s\0" "${array1[#]}" | eval grep -qzFx "$(printf " -e %q" "${array2[#]}")"
But I believe I found a bug in grepv3.1 when matching a newline character with -x flag. If you don't use the newline character, the above line works.
Would you try the following:
array1=(a b c 1 2 3)
array2=(b 1)
declare -A seen # set marks of the elements of array1
for b in "${array2[#]}"; do
(( seen[$b]++ ))
done
for a in "${array1[#]}"; do
(( ${seen[$a]} )) && echo "match" && exit
done
echo "no match"
It may be efficient by avoiding the double loop, although the discussion of efficiency may be meaningless as long as using bash :)
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 an array with subdirs and files:
~$ array=(elem1/a elem1/b elem2/a elem2/b)
I need to select all files (with its subdir) inside subdir elem1.
I've tried with a for loop and case:
for element in "${array[#]}"; do
case $element in
elem1*)
# action I need to perform on this element
echo "This is $element"
;;
esac
done
I'd like to get the list of elements I need using some glob, in a similar way as this (which substracts substrings from array elements):
~$ echo ${array[#]%/a}
elem1 elem1/b elem2 elem2/b
My main concern is that I shoudn't hardcode what strings I'm searching for, as I don't know its contents - in my final version of this script I'm getting them from another array.
My answer prints every element of the array in a different line, then filters the ones you are interested (grep) and put them into a new array
newarray=( $(printf "%s\n" "${array[#]}" | grep ^elem/) )
The only problem would be if the elements of your array (subdirs and file namews) might contain EOL or blank chars.
Bonus
If your elements contain EOL or blank chars, you should use the NUL (\000) char and grep -zZ to handle it; but then you need more code to turn out those NUL-char strings into something which the bash can work with -- the bash stops reading when it finds a NUL char.
In this example I use awk, which has no problem to handle NUL chars, and makes unnecessary the use of grep:
eval newarray=( $(printf "%s\000" "${A[#]}" |
awk 'BEGIN { FS="\000" }
/^elem\// {
gsub("\042","\\\042")
printf("[" NR-1 "]=\042%s\042 ",$0)
}'
)
)
You can filter your array with a variable query (prefix below) and store the results in a new array (result):
#!/bin/bash
array=(elem1/a elem1/b elem2/a elem2/b)
prefix=elem1
result=()
for element in "${array[#]}"; do
[[ $element == $prefix/* ]] && result+=("$element")
done
The result is:
$ declare -p result
declare -a result='([0]="elem1/a" [1]="elem1/b")'
here is one alternative
$ for e in "${array[#]}";
do case "${e%%/*}" in
elem1) echo "$e is in elem1" ;;
esac
done
elem1/a is in elem1
elem1/b is in elem1
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[#]})