the following function in shell script only loops through the first element of the array when called on an array, what's wrong?
#!/bin/sh
in_array(){
a=$2
echo ${#a[#]}
for (( i = 0; i < ${#a[#]} ; i++ ))
do
echo ${a[$i]}
if [ $1 = ${a[$i]} ]
then
return 1
fi
done
return 0
}
exclude_dirs=( aaa bbb )
echo ${#exclude_dirs[#]}
in_array home $exclude_dirs
There are 2 problems. The first is that sh does not support arrays, so your shebang should be changed to a shell that does. (eg, #!/bin/bash). The second problem is more substantial. Arrays are not first class objects in bash (they may be in other shells but I'm going to answer the question for bash, since sh is often bash in many Linux distros and I'm using my crystal ball to determine that you meant bash when you said #!/bin/sh). You can get what you want by using eval. Change your function to something like this:
in_array(){
a=$2
eval "for i in \${$a[#]}; do
echo \$i
test $1 = \$i && return 1
done"
return 0
}
and invoke it without a '$'.
in_array home exclude_dirs
Also, I would strongly recommend inverting the return values. (return 0 if $1 appears in the array, and return 1 if it does not). Either that, or change the function name to "not_it_array". That will allow you to write things like:
if in_array home exclude_dirs; then echo home is excluded; fi
(or use a short circuiting &&). Remember that in sh, 0 is success, and non-zero is failure.
Of course, it would be easier to pass the array by passing all of the values rather than passing the name:
#!/bin/bash
in_array(){
el=$1
shift
while test $# -gt 0; do
test $el = $1 && return 0
shift
done
return 1
}
exclude_dirs=( aaa home bbb )
in_array home ${exclude_dirs[#]} && echo home is excluded
William is right that you can't use arrays in Bourne Shell, but you shouldn't be using eval either. To avoid it you could just simplify your parameter structure:
#!/bin/sh
in_array(){
search_path="$1"
shift
while [ -n "${1+defined}" ]
do
if [ "$1" = "$search_path" ]
then
return 0
fi
shift
done
return 1
}
in_array foo aaa bbb && echo fail test 1
in_array foo foo bar || echo fail test 2
in_array foo bar foo || echo fail test 3
in_array foo foobar && echo fail test 4
in_array foo barfoo && echo fail test 5
in_array foo "foo bar" && echo fail test 6
in_array "foo bar" "foo bar" "baz ban" || echo fail test 7
true
Related
Using:
set -o nounset
Having an indexed array like:
myArray=( "red" "black" "blue" )
What is the shortest way to check if element 1 is set?
I sometimes use the following:
test "${#myArray[#]}" -gt "1" && echo "1 exists" || echo "1 doesn't exist"
I would like to know if there's a preferred one.
How to deal with non-consecutive indexes?
myArray=()
myArray[12]="red"
myArray[51]="black"
myArray[129]="blue"
How to quick check that 51 is already set for example?
How to deal with associative arrays?
declare -A myArray
myArray["key1"]="red"
myArray["key2"]="black"
myArray["key3"]="blue"
How to quick check that key2 is already used for example?
To check if the element is set (applies to both indexed and associative array)
[ "${array[key]+abc}" ] && echo "exists"
Basically what ${array[key]+abc} does is
if array[key] is set, return abc
if array[key] is not set, return nothing
References:
See Parameter Expansion in Bash manual and the little note
if the colon is omitted, the operator tests only for existence [of parameter]
This answer is actually adapted from the answers for this SO question: How to tell if a string is not defined in a bash shell script?
A wrapper function:
exists(){
if [ "$2" != in ]; then
echo "Incorrect usage."
echo "Correct usage: exists {key} in {array}"
return
fi
eval '[ ${'$3'[$1]+muahaha} ]'
}
For example
if ! exists key in array; then echo "No such array element"; fi
From man bash, conditional expressions:
-v varname
True if the shell variable varname is set (has been assigned a value).
example:
declare -A foo
foo[bar]="this is bar"
foo[baz]=""
if [[ -v "foo[bar]" ]] ; then
echo "foo[bar] is set"
fi
if [[ -v "foo[baz]" ]] ; then
echo "foo[baz] is set"
fi
if [[ -v "foo[quux]" ]] ; then
echo "foo[quux] is set"
fi
This will show that both foo[bar] and foo[baz] are set (even though the latter is set to an empty value) and foo[quux] is not.
New answer
From version 4.2 of bash (and newer), there is a new -v option to built-in test command.
From version 4.3, this test could address element of arrays.
array=([12]="red" [51]="black" [129]="blue")
for i in 10 12 30 {50..52} {128..131};do
if [ -v 'array[i]' ];then
echo "Variable 'array[$i]' is defined"
else
echo "Variable 'array[$i]' not exist"
fi
done
Variable 'array[10]' not exist
Variable 'array[12]' is defined
Variable 'array[30]' not exist
Variable 'array[50]' not exist
Variable 'array[51]' is defined
Variable 'array[52]' not exist
Variable 'array[128]' not exist
Variable 'array[129]' is defined
Variable 'array[130]' not exist
Variable 'array[131]' not exist
Note: regarding ssc's comment, I've single quoted 'array[i]' in -v test, in order to satisfy shellcheck's error SC2208. This seem not really required here, because there is no glob character in array[i], anyway...
This work with associative arrays in same way:
declare -A aArray=([foo]="bar" [bar]="baz" [baz]=$'Hello world\041')
for i in alpha bar baz dummy foo test;do
if [ -v 'aArray[$i]' ];then
echo "Variable 'aArray[$i]' is defined"
else
echo "Variable 'aArray[$i]' not exist"
fi
done
Variable 'aArray[alpha]' not exist
Variable 'aArray[bar]' is defined
Variable 'aArray[baz]' is defined
Variable 'aArray[dummy]' not exist
Variable 'aArray[foo]' is defined
Variable 'aArray[test]' not exist
With a little difference:In regular arrays, variable between brackets ([i]) is integer, so dollar symbol ($) is not required, but for associative array, as key is a word, $ is required ([$i])!
Old answer for bash prior to V4.2
Unfortunately, bash give no way to make difference betwen empty and undefined variable.
But there is some ways:
$ array=()
$ array[12]="red"
$ array[51]="black"
$ array[129]="blue"
$ echo ${array[#]}
red black blue
$ echo ${!array[#]}
12 51 129
$ echo "${#array[#]}"
3
$ printf "%s\n" ${!array[#]}|grep -q ^51$ && echo 51 exist
51 exist
$ printf "%s\n" ${!array[#]}|grep -q ^52$ && echo 52 exist
(give no answer)
And for associative array, you could use the same:
$ unset array
$ declare -A array
$ array["key1"]="red"
$ array["key2"]="black"
$ array["key3"]="blue"
$ echo ${array[#]}
blue black red
$ echo ${!array[#]}
key3 key2 key1
$ echo ${#array[#]}
3
$ set | grep ^array=
array=([key3]="blue" [key2]="black" [key1]="red" )
$ printf "%s\n" ${!array[#]}|grep -q ^key2$ && echo key2 exist || echo key2 not exist
key2 exist
$ printf "%s\n" ${!array[#]}|grep -q ^key5$ && echo key5 exist || echo key5 not exist
key5 not exist
You could do the job without the need of externals tools (no printf|grep as pure bash), and why not, build checkIfExist() as a new bash function:
$ checkIfExist() {
eval 'local keys=${!'$1'[#]}';
eval "case '$2' in
${keys// /|}) return 0 ;;
* ) return 1 ;;
esac";
}
$ checkIfExist array key2 && echo exist || echo don\'t
exist
$ checkIfExist array key5 && echo exist || echo don\'t
don't
or even create a new getIfExist bash function that return the desired value and exit with false result-code if desired value not exist:
$ getIfExist() {
eval 'local keys=${!'$1'[#]}';
eval "case '$2' in
${keys// /|}) echo \${$1[$2]};return 0 ;;
* ) return 1 ;;
esac";
}
$ getIfExist array key1
red
$ echo $?
0
$ # now with an empty defined value
$ array["key4"]=""
$ getIfExist array key4
$ echo $?
0
$ getIfExist array key5
$ echo $?
1
What about a -n test and the :- operator?
For example, this script:
#!/usr/bin/env bash
set -e
set -u
declare -A sample
sample["ABC"]=2
sample["DEF"]=3
if [[ -n "${sample['ABC']:-}" ]]; then
echo "ABC is set"
fi
if [[ -n "${sample['DEF']:-}" ]]; then
echo "DEF is set"
fi
if [[ -n "${sample['GHI']:-}" ]]; then
echo "GHI is set"
fi
Prints:
ABC is set
DEF is set
tested in bash 4.3.39(1)-release
declare -A fmap
fmap['foo']="boo"
key='foo'
# should echo foo is set to 'boo'
if [[ -z "${fmap[${key}]}" ]]; then echo "$key is unset in fmap"; else echo "${key} is set to '${fmap[${key}]}'"; fi
key='blah'
# should echo blah is unset in fmap
if [[ -z "${fmap[${key}]}" ]]; then echo "$key is unset in fmap"; else echo "${key} is set to '${fmap[${key}]}'"; fi
Reiterating this from Thamme:
[[ ${array[key]+Y} ]] && echo Y || echo N
This tests if the variable/array element exists, including if it is set to a null value. This works with a wider range of bash versions than -v and doesn't appear sensitive to things like set -u. If you see a "bad array subscript" using this method please post an example.
This is the easiest way I found for scripts.
<search> is the string you want to find, ASSOC_ARRAY the name of the variable holding your associative array.
Dependign on what you want to achieve:
key exists:
if grep -qe "<search>" <(echo "${!ASSOC_ARRAY[#]}"); then echo key is present; fi
key exists not:
if ! grep -qe "<search>" <(echo "${!ASSOC_ARRAY[#]}"); then echo key not present; fi
value exists:
if grep -qe "<search>" <(echo "${ASSOC_ARRAY[#]}"); then echo value is present; fi
value exists not:
if ! grep -qe "<search>" <(echo "${ASSOC_ARRAY[#]}"); then echo value not present; fi
I wrote a function to check if a key exists in an array in Bash:
# Check if array key exists
# Usage: array_key_exists $array_name $key
# Returns: 0 = key exists, 1 = key does NOT exist
function array_key_exists() {
local _array_name="$1"
local _key="$2"
local _cmd='echo ${!'$_array_name'[#]}'
local _array_keys=($(eval $_cmd))
local _key_exists=$(echo " ${_array_keys[#]} " | grep " $_key " &>/dev/null; echo $?)
[[ "$_key_exists" = "0" ]] && return 0 || return 1
}
Example
declare -A my_array
my_array['foo']="bar"
if [[ "$(array_key_exists 'my_array' 'foo'; echo $?)" = "0" ]]; then
echo "OK"
else
echo "ERROR"
fi
Tested with GNU bash, version 4.1.5(1)-release (i486-pc-linux-gnu)
For all time people, once and for all.
There's a "clean code" long way, and there is a shorter, more concise, bash centered way.
$1 = The index or key you are looking for.
$2 = The array / map passed in by reference.
function hasKey ()
{
local -r needle="${1:?}"
local -nr haystack=${2:?}
for key in "${!haystack[#]}"; do
if [[ $key == $needle ]] ;
return 0
fi
done
return 1
}
A linear search can be replaced by a binary search, which would perform better with larger data sets. Simply count and sort the keys first, then do a classic binary halving of of the haystack as you get closer and closer to the answer.
Now, for the purist out there that is like "No, I want the more performant version because I may have to deal with large arrays in bash," lets look at a more bash centered solution, but one that maintains clean code and the flexibility to deal with arrays or maps.
function hasKey ()
{
local -r needle="${1:?}"
local -nr haystack=${2:?}
[ -n ${haystack["$needle"]+found} ]
}
The line [ -n ${haystack["$needle"]+found} ]uses the ${parameter+word} form of bash variable expansion, not the ${parameter:+word} form, which attempts to test the value of a key, too, which is not the matter at hand.
Usage
local -A person=(firstname Anthony lastname Rutledge)
if hasMapKey "firstname" person; then
# Do something
fi
When not performing substring expansion, using the form described
below (e.g., ‘:-’), Bash tests for a parameter that is unset or null.
Omitting the colon results in a test only for a parameter that is
unset. Put another way, if the colon is included, the operator tests
for both parameter’s existence and that its value is not null; if the
colon is omitted, the operator tests only for existence.
${parameter:-word}
If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter is substituted.
${parameter:=word}
If parameter is unset or null, the expansion of word is assigned to parameter. The value of parameter is then substituted. Positional
parameters and special parameters may not be assigned to in this way.
${parameter:?word}
If parameter is null or unset, the expansion of word (or a message to that effect if word is not present) is written to the standard
error and the shell, if it is not interactive, exits. Otherwise, the
value of parameter is substituted. ${parameter:+word}
If parameter is null or unset, nothing is substituted, otherwise the expansion of word is substituted.
https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html#Shell-Parameter-Expansion
If $needle does not exist expand to nothing, otherwise expand to the non-zero length string, "found". This will make the -n test succeed if the $needle in fact does exist (as I say "found"), and fail otherwise.
Both in the case of arrays and hash maps I find the easiest and more straightforward solution is to use the matching operator =~.
For arrays:
myArray=("red" "black" "blue")
if [[ " ${myArray[#]} " =~ " blue " ]]; then
echo "blue exists in myArray"
else
echo "blue does not exist in myArray"
fi
NOTE: The spaces around the array guarantee the first and last element can match. The spaces around the value guarantee an exact match.
For hash maps, it's actually the same solution since printing a hash map as a string gives you a list of its values.
declare -A myMap
myMap=(
["key1"]="red"
["key2"]="black"
["key3"]="blue"
)
if [[ " ${myMap[#]} " =~ " blue " ]]; then
echo "blue exists in myMap"
else
echo "blue does not exist in myMap"
fi
But what if you would like to check whether a key exists in a hash map? In the case you can use the ! operator which gives you the list of keys in a hash map.
if [[ " ${!myMap[#]} " =~ " key3 " ]]; then
echo "key3 exists in myMap"
else
echo "key3 does not exist in myMap"
fi
I get bad array subscript error when the key I'm checking is not set. So, I wrote a function that loops over the keys:
#!/usr/bin/env bash
declare -A helpList
function get_help(){
target="$1"
for key in "${!helpList[#]}";do
if [[ "$key" == "$target" ]];then
echo "${helpList["$target"]}"
return;
fi
done
}
targetValue="$(get_help command_name)"
if [[ -z "$targetvalue" ]];then
echo "command_name is not set"
fi
It echos the value when it is found & echos nothing when not found. All the other solutions I tried gave me that error.
I want to create a bash function that iterates over an array and returns 0 if an element passed as argument does not exist in the array, or 1 otherwise.
The following code however does not print anything on stdout.
function checkparsed {
tocheck="$1"
shift
for item in $#
do
if [ "$item" = "$tocheck" ]; then
return 0
fi
done
return 1
}
mdfiles=('foo')
echo "$(checkparsed foo ${mdfiles[#]})"
You are capturing the output of the function (there is none).
To print 0 or 1, either echo them in the function directly (don't forget to return), or use echo $? after running the function.
To handle spaces and glob characters in elements in ${mdfiles[#]}, you should use double quotes:
for item in "$#"
# and
checkparsed foo "${mdfiles[#]}"
This line is the issue:
echo "$(checkparsed foo ${mdfiles[#]})"
since your function is not echoing anything but you are returning values 0 or 1.
You actually need to check for $? for the return value from your function:
checkparsed foo ${mdfiles[#]}
echo $?
0
Or else use return value in condition evaluation:
checkparsed foo ${mdfiles[#]} && echo "found" || echo "not found"
found
checkparsed food ${mdfiles[#]} && echo "found" || echo "not found"
not found
The Question:
In bash scripting, what is the best way to convert a string, containing literal quotes surrounding multiple words, into an array with the same result of parsed arguments?
The Controversy:
Many questions exist all applying evasive tactics to avoid the problem instead of finding a solution, this question raises the following arguments and would like to encourage the reader to focus on arguments and if you are up for it, partake in the challenge to find the optimum solution.
Arguments raised:
Although there are many scenarios where this pattern should be avoided, because there exists alternative solutions better suited, the author is of the opinion that valid use cases still remain. This question will attempt to produce one such use case, but make no claim to the viability thereof only that it is a conceivable scenario which may present itself in a real world situation.
You must find the optimum solution to satisfy the requirement. The use case was chosen specifically for its real world applications. You may not agree with the decisions that were made but are not tasked to give an opinion only to deliver the solution.
Satisfy the requirement without modifying the input or choice of transport. Both specifically chosen with a real world scenario to defend the narrative that those parts are out of your control.
No answers exist to the particular problem and this question aims to address that. If you are inclined to avoid this pattern then simply avoid the question but if you think you are up for the challenge lets see how you would approach the problem.
The Valid use case:
Converting an existing script currently in use to receive parameters via named pipe or similar stream. In order to minimize the impact on the myriad of scripts outside of the developers control a decision was made to not change the interface. Existing scripts must be able to pass the same arguments via the new stream implementation as they did before.
Existing implementation:
$ ./string2array arg1 arg2 arg3
args=(
[0]="arg1"
[1]="arg2"
[2]="arg3"
)
Required change:
$ echo "arg1 arg2 arg3" | ./string2array
args=(
[0]="arg1"
[1]="arg2"
[2]="arg3"
)
The problem:
As pointed out by Bash and Double-Quotes passing to argv literal quotes are not parsed as would be expected.
This workbench script can be used to test various solutions, it handles the transport and formulates a measurable response. It is suggested that you focus on the solution script which gets sourced with the string as argument and you should populate the $args variable as an array.
The string2array workbench script:
#!/usr/bin/env bash
#string2arry
args=()
function inspect() {
local inspct=$(declare -p args)
inspct=${inspct//\[/\\n\\t[}; inspct=${inspct//\'/}; inspct="${inspct:0:-1}\n)"
echo -e ${inspct#*-a }
}
while read -r; do
# source the solution to turn $REPLY in $args array
source $1 "${REPLY}"
inspect
done
Standard solution - FAILS
The solution for turning a string into a space delimited array of words worked for our first example above:
#solution1
args=($#)
Undesired result
Unfortunately the standard solution produces an undesired result for quoted multi word arguments:
$ echo 'arg1 "multi arg 2" arg3' | ./string2array solution1
args=(
[0]="arg1"
[1]="\"multi"
[2]="arg"
[3]="2\""
[4]="arg3"
)
The Challenge:
Using the workbench script provide a solution snippet that will produce the following result for the arguments received.
Desired result:
$ echo 'arg1 "multi arg 2" arg3' | ./string2array solution-xyz
args=(
[0]="arg1"
[1]="multi arg 2"
[2]="arg3"
)
The solution should be compatible with standard argument parsing in every way. The following unit test should pass for for the provided solution. If you can think of anything currently missing from the unit test please leave a comment and we can update it.
Unit test for the requirements
Update: Test simplified and includes the Johnathan Leffer test
#!/usr/bin/env bash
#test_string2array
solution=$1
function test() {
cmd="echo \"${1}\" | ./string2array $solution"
echo "$ ${cmd}"
echo ${1} | ./string2array $solution > /tmp/t
cat /tmp/t
echo -n "Result : "
[[ $(cat /tmp/t|wc -l) -eq 7 ]] && echo "PASSED!" || echo "FAILED!"
}
echo 1. Testing single args
test 'arg1 arg2 arg3 arg4 arg5'
echo
echo 2. Testing multi args \" quoted
test 'arg1 "multi arg 2" arg3 "a r g 4" arg5'
echo
echo 3 Testing multi args \' quoted
test "arg1 'multi arg 2' arg3 'a r g 4' arg5"
echo
echo 4 Johnathan Leffer test
test "He said, \"Don't do that!\" but \"they didn't listen.\""
The declare built-in seems to do what you want; in my test, it's your inspect function that doesn't seem work to properly test all inputs:
# solution3
declare -a "args=($1)"
Then
$ echo "arg1 'arg2a arg2b' arg3" | while read -r; do
> source solution3 "${REPLY}"
> for arg in "${args[#]}"; do
> echo "Arg $((++i)): $arg"
> done
> done
Arg 1: arg1
Arg 2: arg2a arg2b
Arg 3: arg3
You may do it with declare instead of eval, for example:
Instead of:
string='"aString that may haveSpaces IN IT" bar foo "bamboo" "bam boo"'
echo "Initial string: $string"
eval 'for word in '$string'; do echo $word; done'
Do:
declare -a "array=($string)"
for item in "${array[#]}"; do echo "[$item]"; done
But please note, it is not much safer if input comes from user!
So, if you try it with say string like:
string='"aString that may haveSpaces IN IT" bar foo "bamboo" "bam boo" `hostname`'
You get hostname evaluated (there off course may be something like rm -rf /)!
Very-very simple attempt to guard it just replace chars like backtrick ` and $:
string='"aString that may haveSpaces IN IT" bar foo "bamboo" "bam boo" `hostname`'
declare -a "array=( $(echo $string | tr '`$<>' '????') )"
for item in "${array[#]}"; do echo "[$item]"; done
Now you got output like:
[aString that may haveSpaces IN IT]
[bar]
[foo]
[bamboo]
[bam boo]
[?hostname?]
More details about methods and pros about using different methods you may found in that good answer: Why should eval be avoided in Bash, and what should I use instead?
See also https://superuser.com/questions/1066455/how-to-split-a-string-with-quotes-like-command-arguments-in-bash/1186997#1186997
But there still leaved vector for attack.
I very would have in bash method of string quote like in double quotes (") but without interpreting content.
First attempt
Populate a variable with the combined words once the open quote was detected and only append to the array once the close quote arrives.
Solution
#solution2
j=''
for a in ${1}; do
if [ -n "$j" ]; then
[[ $a =~ ^(.*)[\"\']$ ]] && {
args+=("$j ${BASH_REMATCH[1]}")
j=''
} || j+=" $a"
elif [[ $a =~ ^[\"\'](.*)$ ]]; then
j=${BASH_REMATCH[1]}
else
args+=($a)
fi
done
Unit test results:
$ ./test_string2array solution2
1. Testing single args
$ echo "arg1 arg2 arg3 arg4 arg5" | ./string2array solution2
args=(
[0]="arg1"
[1]="arg2"
[2]="arg3"
[3]="arg4"
[4]="arg5"
)
Result : PASSED!
2. Testing multi args " quoted
$ echo 'arg1 "multi arg 2" arg3 "a r g 4" arg5' | ./string2array solution2
args=(
[0]="arg1"
[1]="multi arg 2"
[2]="arg3"
[3]="a r g 4"
[4]="arg5"
)
Result : PASSED!
3 Testing multi args ' quoted
$ echo "arg1 'multi arg 2' arg3 'a r g 4' arg5" | ./string2array solution2
args=(
[0]="arg1"
[1]="multi arg 2"
[2]="arg3"
[3]="a r g 4"
[4]="arg5"
)
Result : PASSED!
So I think xargs actually works for all your test cases, eg:
echo 'arg1 "multi arg 2" arg3' | xargs -0 ./string2array
Second attempt
Append the element in place without the need for an additional variable.
#solution3
for i in $1; do
[[ $i =~ ^[\"\'] ]] && args+=(' ')
lst=$(( ${#args[#]}-1 ))
[[ "${args[*]}" =~ [[:space:]]$ ]] && args[$lst]+="${i/[\"\']/} " || args+=($i)
[[ $i =~ [\"\']$ ]] && args[$lst]=${args[$lst]:1:-1}
done
Modify in place
Let bash convert the string to array and then loop through to fix it.
args=($#) cnt=${#args[#]} idx=-1 chr=
for (( i=0; i<cnt; i++ )); do
[[ $idx -lt 0 ]] && {
[[ ${args[$i]:0:1} =~ [\'\"] ]] && \
idx=$i chr=${args[$idx]:0:1} args[$idx]="${args[$idx]:1}"
continue
}
args[$idx]+=" ${args[$i]}"
unset args[$i]
[[ ${args[$idx]: -1:1} == $chr ]] && args[$idx]=${args[$idx]:0:-1} idx=-1
done
Modify the delimiter
In this solution we turn the spaces into commas, remove the quotes and reset the spaces for the multi word arguments, to allow for the correct argument parsing.
#solution4
s=${*//[[:space:]]/\l}
while [[ $s =~ [\"\']([^\"\']*)[\"\'] ]]; do
s=${s/$BASH_REMATCH/${BASH_REMATCH[1]//\l/ }}
done
IFS=\l
args=(${s})
NEEDS WORK!!
I am making a bash script and I have encountered a problem. So let's say I got this
function create_some_array(){
for i in 0 1 2 3 .. 10
do
a[i]=$i
done
}
create_some_array
echo ${a[*]}
Is there any way I can make this work? I have searched quite a lot and nothing I found worked.
I think making the a[] a global variable should work but I can't find something that actually works in my code. Is there any way to return the array from the function to main program?
Thanks in advance
This won't work as expected when there are whitespaces in the arrays:
function create_some_array() {
local -a a=()
for i in $(seq $1 $2); do
a[i]="$i $[$i*$i]"
done
echo ${a[#]}
}
and worse: if you try to get array indices from the outside "a", it turns out to be a scalar:
echo ${!a[#]}
even assignment as an array wont help, as possible quoting is naturally removed by the echo line and evaluation order cannot be manipulated to escape quoting: try
function create_some_array() {
...
echo "${a[#]}"
}
a=($(create_some_array 0 10))
echo ${!a[#]}
Still, printf seems not to help either:
function create_some_array() {
...
printf " \"%s\"" "${a[#]}"
}
seems to produce correct output on one hand:
$ create_some_array 0 3; echo
"0 0" "1 1" "2 4" "3 9"
but assignment doesn't work on the other:
$ b=($(create_some_array 0 3))
$ echo ${!b[#]}
0 1 2 3 4 5 6 7
So my last trick was to do assignment as follows:
$ eval b=("$(create_some_array 0 3)")
$ echo -e "${!b[#]}\n${b[3]}"
0 1 2 3
3 9
Tataaa!
P.S.: printf "%q " "${a[#]}" also works fine...
This works fine as described. The most likely reason it doesn't work in your actual code is because you happen to run it in a subshell:
cat textfile | create_some_array
echo ${a[*]}
would not work, because each element in a pipeline runs in a subshell, and
myvalue=$(create_some_array)
echo ${a[*]}
would not work, since command expansion happens in a subshell.
You can make an array local to a function, and then return it:
function create_some_array(){
local -a a=()
for i in $(seq $1 $2); do
a[i]=$i
done
echo ${a[#]}
}
declare -a a=()
a=$(create_some_array 0 10)
for i in ${a[#]}; do
echo "i = " $i
done
Hi here is my solution:
show(){
local array=()
array+=("hi")
array+=("everything")
array+=("well?")
echo "${array[#]}"
}
for e in $(show);do
echo $e
done
Try this code on: https://www.tutorialspoint.com/execute_bash_online.php
Both these work for me with sh and bash:
arr1=("192.168.3.4" "192.168.3.4" "192.168.3.3")
strArr=$(removeDupes arr1) # strArr is a string
for item in $strArr; do arr2+=("$item"); done # convert it to an array
len2=${#arr2[#]} # get array length
echo "${len2}" # echo length
eval arr3=("$(removeDupes arr1)") # shellcheck does not like this line and won't suppress it but it works
len3=${#arr3[#]} # get array length
echo "${len3}" # echo length
As an aside, the removeDupes function looks like this:
removeDupes() {
arg="$1[#]"
arr=("${!arg}")
len=${#arr[#]}
resultArr=()
# some array manipulation here
echo "${resultArr[#]}"
}
This answer is based on but better explains and simplifies the answers from #Hans and #didierc
Bash 4 on Linux ~
I have an array of possible values. I must restrict user input to these values.
Arr=(hello kitty goodbye quick fox)
User supplies value as argument to script:
bash myscript.sh -b var
Currently, I'm trying the following:
function func_exists () {
_var="$1"
for i in ${Arr[#]}
do
if [ "$i" == "$_var" ]
then
echo hooray for "$_var"
return 1
fi
done
return 0
}
func_exists $var
if [ $? -ne 1 ];then
echo "Not a permitted value."
func_help
exit $E_OPTERROR
fi
Seems to work fine, are there better methods for testing user input against an array of allowed values?
UPDATE: I like John K's answer ...can someone clarify the use of $#? I understand that this represents all positional parameters -- so we shift the first param off the stack and $# now represents all remaining params, those being the passed array ...is that correct? I hate blindly using code without understanding ...even if it works!
Your solution is what I'd do. Maybe using a few more shell-isms, such as returning 0 for success and non-0 for failure like UNIX commands do in general.
# Tests if $1 is in the array ($2 $3 $4 ...).
is_in() {
value=$1
shift
for i in "$#"; do
[[ $i == $value ]] && return 0
done
return 1
}
if ! is_in "$var" "${Arr[#]}"; then
echo "Not a permitted value." >&2
func_help
exit $E_OPTERROR
fi
Careful use of double quotes makes sure this will work even if the individual array entries contain spaces, which is allowed. This is a two element array: list=('hello world' 'foo bar').
Another solution. is_in is just a variable:
Arr=(hello kitty goodbye quick fox)
var='quick'
string=" ${Arr[*]} " # array to string, framed with blanks
is_in=1 # false
# try to delete the variable inside the string; true if length differ
[ "$string" != "${string/ ${var} /}" ] && is_in=0
echo -e "$is_in"
function func_exists () {
case "$1"
in
hello)
kitty)
goodbye)
quick)
fox)
return 1;;
*)
return 0;;
esac
}