163
votes
Accepted
how to count the length of an array defined in bash?
You can access the array indices using ${!array[@]} and the length of the array using ${#array[@]}, e.g. :
#!/bin/bash
array=( item1 item2 item3 )
for index in ${!array[@]}; do
echo $index/${#...
- 72.1k
150
votes
Accepted
Is there a way of reading the last element of an array with bash?
As of bash 4.2, you can just use a negative index ${myarray[-1]} to get the last element. You can do the same thing for the second-last, and so on; in Bash:
If the subscript used to reference an ...
- 70.2k
128
votes
How to add/remove an element to/from the array in bash?
To add an element to the beginning of an array use.
arr=("new_element" "${arr[@]}")
Generally, you would do.
arr=("new_element1" "new_element2" "..." "new_elementN" "${arr[@]}")
To add an element ...
- 38.2k
94
votes
Accepted
`Syntax error: "(" unexpected` when creating an array
When you use ./scriptname.sh it executes with /bin/bash as in the first line with #!. But when you use sh scriptname.sh it executes sh, not bash.
The sh shell has no syntax to create arrays, but Bash ...
- 1,298
62
votes
Accepted
Arrays in Unix Bourne Shell
/bin/sh is hardly ever a Bourne shell on any systems nowadays (even Solaris which was one of the last major system to include it has now switched to a POSIX sh for its /bin/sh in Solaris 11). /bin/sh ...
- 465k
58
votes
Is there a way of reading the last element of an array with bash?
Modern bash (v4.1 or better)
You can read the last element at index -1:
$ a=(a b c d e f)
$ echo ${a[-1]}
f
Support for accessing numerically-indexed arrays from the end using negative indexes ...
- 69.1k
54
votes
Bash to check if directory exist. If not create with an array
Just use:
mkdir -p -- "${array1[@]}"
That will also create intermediary directory components if need be so your array can also be shortened to only include the leaf directories:
array1=(
/apache/...
- 465k
42
votes
Accepted
Is there a reason why the first element of a Zsh array is indexed by 1 instead of 0?
Virtually all shell arrays (Bourne, csh, tcsh, fish, rc, es, yash) start at 1. ksh is the only exception that I know (bash just copied ksh).
Most interpreted languages at the time (early 90s): awk, ...
- 465k
40
votes
sh + how to use array in sh script in order to print all values in array
Little late, but I don't see the ideal sh answer here so I'll chime in. If you don't need subscripting, then sh effectively does support arrays. It just supports them as space separated strings. You ...
- 641
37
votes
Accepted
Delete an array in awk
The syntax
delete array
is not in current versions in POSIX, but it is supported by virtually all existing implementations (including the original awk, GNU, mawk, and BusyBox). It will be added in a ...
30
votes
Accepted
What is the difference between [@] and [*] when referencing bash array values?
The difference is subtle; "${LIST[*]}" (like "$*") creates one argument, while "${LIST[@]}" (like "$@") will expand each item into separate arguments, so:
LIST=(...
- 8,456
29
votes
how to shift array value in bash
To answer the question in the title, you can "shift" an array with the substring/subarray notation. shift itself works with just the positional parameters.
$ a=(a b c d e)
$ a=("${a[@]:...
- 114k
28
votes
Accepted
How do I test if an item is in a bash array?
Use a different kind of array: rather than an integer-indexed array, use an associative array, so the key (index) is what you will be checking for. bash-4.0 or later is required for this.
declare -A ...
- 9,241
28
votes
Accepted
parse one field from an JSON array into bash array
Using jq :
$ cat json
[
{
"item1": "value1",
"item2": "value2",
"sub items": [
{
"subitem": "subvalue"
}
]
},
{
"item1": "value1_2",
"item2": "...
- 24.5k
27
votes
Accepted
What is the difference between $path and $PATH (lowercase versus uppercase) with zsh?
That's a feature of zsh inherited from csh/tcsh.
The $path array variable is tied to the $PATH scalar (string) variable. Any modification on one is reflected in the other.
In zsh (contrary to (t)csh)...
- 465k
26
votes
Accepted
Provide two arguments to one option using getopts
You cannot pass two arguments with single option using getopts.
I recommend the following alternatives:
Put quotes around multiple arguments
In this case getopts will treat them as one argument, ...
- 43.1k
26
votes
Accepted
BASH associative array printing
I think you're asking two different things there.
Is there a way to make bash print this info without the loop?
Yes, but they are not as good as just using the loop.
Is there a cleaner way to ...
- 114k
25
votes
Accepted
Single parenthesis in bash variable assignment
In your case parenthesis () are used as array definition, for example
a=(one two three) # array definition
echo "${a}" # print first element of array a
echo "${a[0]}" # print first ...
- 43.1k
25
votes
Bash - reverse an array
Another unconventional approach:
#!/bin/bash
array=(1 2 3 4 5 6 7)
f() { array=("${BASH_ARGV[@]}"); }
shopt -s extdebug
f "${array[@]}"
shopt -u extdebug
echo "${array[@]}"
Output:
7 6 5 4 3 2 ...
- 11.2k
25
votes
Accepted
What type of operation is /#/- in "${my_array[@]/#/-}"?
This is an instance of pattern replacement in shell parameter expansion: ${parameter/pattern/replacement} expands ${parameter}, replacing the first instance of pattern with replacement. In the context ...
- 353k
24
votes
Bash - reverse an array
Unconventional approach (all not pure bash):
if all elements in an array are just one characters (like in the question) you can use rev:
echo "${array[@]}" | rev
otherwise:
printf '%s\n' "${array[@...
- 43.1k
22
votes
Accepted
How do I shift a bash array at some index in the middle?
unset removes an element. It doesn't renumber the remaining elements.
We can use declare -p to see exactly what happens to numbers:
$ unset "numbers[i]"
$ declare -p numbers
declare -a numbers=([0]=...
- 69.1k
21
votes
Is there a way of reading the last element of an array with bash?
bash array assignment, reference, unsetting with negative index were only added in bash 4.3. With older version of bash, you can use expression in index array[${#array[@]-1}]
Another way, also work ...
- 143k
19
votes
Accepted
Print all words on lines of a file in reverse order
All examples presented below work for general case where there's an arbitrary number of words on the line. The essential idea is the same everywhere - we have to read the file line by line and print ...
- 15.3k
19
votes
Accepted
Possible bug in Bash?: foo() { echo "${var[0]}"; }; var=(bar baz) foo
Generally calling:
var=value cmd
where cmd is a function is not portable.
With bash, that only works for scalar variables (and with x=(...) parsed as an array but assigned as a scalar) and there ...
- 465k
19
votes
Accepted
Bash - reverse an array
I have answered the question as written, and this code reverses the array. (Printing the elements in reverse order without reversing the array is just a for loop counting down from the last element to ...
- 88.8k
18
votes
How do I test if an item is in a bash array?
The straightforward way is to iterate with a loop :
var=ab
for item in "${array[@]}"; do
[[ $var == "$item" ]] && echo "$var present in the array"
done
- 24.5k
18
votes
Append (alter) each array element via parameter expansion (i.e. without printf)?
Use $^array.
It turns the array into a sort of brace expansion of the array. As in when a=(foo bar baz), $^a would be a bit like {foo,bar,baz}.
$ a=(foo bar baz)
$ echo prefix${^a}suffix
...
- 465k
17
votes
Accepted
Go from a String to an Array of "words" in Bash
VotePedro="Vote for Pedro"
votePedroArray=(${VotePedro})
Explanation:
Arrays are usually declared using parentheses. For example votePedroArray=("Vote" "For" "Pedro") would give you an array of ...
- 580
16
votes
Accepted
splitting a line into array in bash with tab as delimiter
The array assignment tmp=(${line///}) splits the value on whatever characters IFS contains, which by default includes tabs, and spaces and newlines. (I don't see what the empty substitution does.) To ...
- 114k
Only top scored, non community-wiki answers of a minimum length are eligible