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I am trying to define a local array in a bash function and access it outside that function.
I realise that BASH functions do not return values but I can assign the results of a calculation to a global value. I expected this code to echo the content of array[] to the screen. I'm not sure why its failing.
function returnarray
{
local array=(foo doo coo)
#echo "inside ${array[#]}"
}
targetvalue=$(returnarray)
echo ${targetvalue[#]}
You have two options. The first one is what #choroba prescribes, and it's probably the best and simplest: don't define your array local.
returnarray() {
array=(foo doo coo) # NOT local
}
# call your function
returnarray
# now the array is in array and you may copy it for later use as follows:
targetvalue=( "${array[#]}" )
# print it to check:
declare -p targetvalue
This is neat, simple, safe, completely avoids the use of subshells (so it's more efficient). It has one caveat, though: it won't work with sparse arrays (but this should be a minor detail). There's another tiny disadvantage: the array needs to be copied.
Another option is to pass a variable name to your function, and have the function generate the array directly. This uses namerefs and is only available since Bash 4.3 (but it's really good—use it if you can!):
generatearray() {
# $1 is array name in which array is generated
local -n array="$1" || return 1
array=( foo doo coo )
}
# call function that constructs the array with the array name
generatearray targetvalue
# display it
declare -p targetvalue
To make the variable accessible from outside, don't declare it local. Make it global.
First, as you say, there are no return values of bash functions. So the only way to pass a local value is to echo it.
However, this would lead to your targetvalue having everything you echoed in index 0 if interpreted as an array. To tell bash to treat the parts as array parts, you have to surround them by parentheses - from the bash manual:
Arrays are assigned to using compound assignments of the form
name=(value1 ... valuen), where each value is of the form [sub‐
script]=string.
#!/bin/bash
function returnarray
{
local array=(foo doo coo)
echo "${array[#]}"
}
targetvalue=($(returnarray))
echo ${targetvalue[#]}
echo ${targetvalue[1]}
However, all of this is really programming around how bash works. It will be better to define your arrays globally.
As the use of echo makes bash interpret the values, this only works, if the values of the array are not affected by bash, for example the values may not contain wildcards or spaces, wildcards would be expanded to matching files and spaces in a value would translate into multiple array values.
Look at this, it might be ok with spaces and other characters....
#!/bin/bash
function returnarray
{
newname=$1
local array=(foo doo coo)
declare -p array | sed "s/array/$newname/g"
}
eval $(returnarray glob)
echo elm0 ${glob[0]}
echo elm1 ${glob[1]}
echo elm2 ${glob[2]}
See How to return an array in bash without using globals?
Edit: the comment about 'array' was correct... here is a fixed version. sed usage I dont mind...
#!/bin/bash
function returnarray
{
newname=$1
local array=(foo doo coo "declare -a array" aa)
declare -p array | sed "s/^declare -a array/declare -a $newname/"
}
eval $(returnarray glob)
echo elm0 ${glob[0]}
echo elm1 ${glob[1]}
echo elm2 ${glob[2]}
echo elm2 ${glob[3]}
echo elm2 ${glob[4]}
You can declare local variables, and then printf a comma-separated-value string, which converts nicely to an array. The key is using printf instead of echo.
http://wiki.bash-hackers.org/commands/builtin/read :
printf is used, because (depending on settings), echo may interpret some baskslash-escapes or switches (like -n).
Code:
#Return csv of project.id's
function get_project() {
local qry="select id from ${DB}.projects where identifier=\"${1}\";"
local ids=`sudo -u ${DB_USER} ${DB_LOCATION} -u ${DB_USER} -p${DB_PASS} -s -e "${qry}"`
#return
while read -r element; do printf "%s," "$element"; done <<< "$ids"
}
#Return csv of member.id's
function get_members() {
local qry="select user_id from ${DB}.members where project_id=${1};"
local ids=`sudo -u ${DB_USER} ${DB_LOCATION} -u ${DB_USER} -p${DB_PASS} -s -e "${qry}"`
#return
while read -r element; do printf "%s," "$element"; done <<< "$ids"
}
projects=( $(get_project "newuser1") )
declare -p projects
member_ids=( $(get_members $projects) )
declare -p member_ids
Terminal:
root#dev:~# ./batch_memberships.sh
declare -a projects='([0]="439")'
declare -a member_ids='([0]="315" [1]="1")'
I give an array as a parameter to a function like this:
declare -a my_array=(1 2 3 4)
my_function (????my_array)
I want the array to be passed to the function just as one array, not as 4 separate argument. Then in the function, I want to iterate through the array like:
(in my_function)
for item in (???)
do
....
done
What should be the correct syntax for (???).
bash does not have a syntax for array literals. What you show (my_function (1 2 3 4)) is a syntax error. You must use one of
my_function "(1 2 3 4)"
my_function 1 2 3 4
For the first:
my_function() {
local -a ary=$1
# do something with the array
for idx in "${!ary[#]}"; do echo "ary[$idx]=${ary[$idx]}"; done
}
For the second, simply use "$#" or:
my_function() {
local -a ary=("$#")
# do something with the array
for idx in "${!ary[#]}"; do echo "ary[$idx]=${ary[$idx]}"; done
}
A reluctant edit...
my_function() {
local -a ary=($1) # $1 must not be quoted
# ...
}
declare -a my_array=(1 2 3 4)
my_function "${my_array[#]}" # this *must* be quoted
This relies on your data NOT containing whitespace. For example this won't work
my_array=("first arg" "second arg")
You want to pass 2 elements but you will receive 4. Coercing an array into a string and then re-expanding it is fraught with peril.
You can do this with indirect variables, but they are ugly with arrays
my_function() {
local tmp="${1}[#]" # just a string here
local -a ary=("${!tmp}") # indirectly expanded into a variable
# ...
}
my_function my_array # pass the array *name*
Assigning arrays to variables in Bash script seems rather complicated:
a=("a" "b" "c")
b=$a
echo ${a[0]}
echo ${a[1]}
echo ${b[0]}
echo ${b[1]}
leads to
a
b
a
instead of
a
b
a
b
Why? How can I fix it?
If you want to copy a variable that holds an array to another name, you do it like this:
a=('a' 'b' 'c')
b=( "${a[#]}" )
Why?
If a is an array, $a expands to the first element in the array. That is why b in your example only has one value. In bash, variables that refer to arrays aren't assignable like pointers would be in C++ or Java. Instead variables expand (as in Parameter Expansion) into strings and those strings are copied and associated with the variable being assigned.
How can I fix it?
To copy a sparse array that contains values with spaces, the array must be copied one element at a time by the indices - which can be obtained with ${!a[#]}.
declare -a b=()
for i in ${!a[#]}; do
b[$i]="${a[$i]}"
done
From the bash man page:
It is possible to obtain the keys (indices) of an array as well as the values.
${!name[#]} and ${!name[*]} expand to the indices assigned in array variable name.
The treatment when in double quotes is similar to the expansion of the special
parameters # and * within double quotes.
Here's a script you can test on your own:
#!/bin/bash
declare -a a=();
a[1]='red hat'
a[3]='fedora core'
declare -a b=();
# Copy method that works for sparse arrays with spaces in the values.
for i in ${!a[#]}; do
b[$i]="${a[$i]}"
done
# does not work, but as LeVar Burton says ...
#b=("${a[#]}")
echo a indicies: ${!a[#]}
echo b indicies: ${!b[#]}
echo "values in b:"
for u in "${b[#]}"; do
echo $u
done
Prints:
a indicies: 1 3
b indicies: 1 3 # or 0 1 with line uncommented
values in b:
red hat
fedora core
This also works for associative arrays in bash 4, if you use declare -A (with capital A instead of lower case) when declaring the arrays.
I have a function that creates an array and I want to return the array to the caller:
create_array() {
local my_list=("a", "b", "c")
echo "${my_list[#]}"
}
my_algorithm() {
local result=$(create_array)
}
With this, I only get an expanded string. How can I "return" my_list without using anything global?
With Bash version 4.3 and above, you can make use of a nameref so that the caller can pass in the array name and the callee can use a nameref to populate the named array, indirectly.
#!/usr/bin/env bash
create_array() {
local -n arr=$1 # use nameref for indirection
arr=(one "two three" four)
}
use_array() {
local my_array
create_array my_array # call function to populate the array
echo "inside use_array"
declare -p my_array # test the array
}
use_array # call the main function
Produces the output:
inside use_array
declare -a my_array=([0]="one" [1]="two three" [2]="four")
You could make the function update an existing array as well:
update_array() {
local -n arr=$1 # use nameref for indirection
arr+=("two three" four) # update the array
}
use_array() {
local my_array=(one)
update_array my_array # call function to update the array
}
This is a more elegant and efficient approach since we don't need command substitution $() to grab the standard output of the function being called. It also helps if the function were to return more than one output - we can simply use as many namerefs as the number of outputs.
Here is what the Bash Manual says about nameref:
A variable can be assigned the nameref attribute using the -n option
to the declare or local builtin commands (see Bash Builtins) to create
a nameref, or a reference to another variable. This allows variables
to be manipulated indirectly. Whenever the nameref variable is
referenced, assigned to, unset, or has its attributes modified (other
than using or changing the nameref attribute itself), the operation is
actually performed on the variable specified by the nameref variable’s
value. A nameref is commonly used within shell functions to refer to a
variable whose name is passed as an argument to the function. For
instance, if a variable name is passed to a shell function as its
first argument, running
declare -n ref=$1 inside the function creates a nameref variable ref
whose value is the variable name passed as the first argument.
References and assignments to ref, and changes to its attributes, are
treated as references, assignments, and attribute modifications to the
variable whose name was passed as $1.
What's wrong with globals?
Returning arrays is really not practical. There are lots of pitfalls.
That said, here's one technique that works if it's OK that the variable have the same name:
$ f () { local a; a=(abc 'def ghi' jkl); declare -p a; }
$ g () { local a; eval $(f); declare -p a; }
$ f; declare -p a; echo; g; declare -p a
declare -a a='([0]="abc" [1]="def ghi" [2]="jkl")'
-bash: declare: a: not found
declare -a a='([0]="abc" [1]="def ghi" [2]="jkl")'
-bash: declare: a: not found
The declare -p commands (except for the one in f() are used to display the state of the array for demonstration purposes. In f() it's used as the mechanism to return the array.
If you need the array to have a different name, you can do something like this:
$ g () { local b r; r=$(f); r="declare -a b=${r#*=}"; eval "$r"; declare -p a; declare -p b; }
$ f; declare -p a; echo; g; declare -p a
declare -a a='([0]="abc" [1]="def ghi" [2]="jkl")'
-bash: declare: a: not found
-bash: declare: a: not found
declare -a b='([0]="abc" [1]="def ghi" [2]="jkl")'
-bash: declare: a: not found
Bash can't pass around data structures as return values. A return value must be a numeric exit status between 0-255. However, you can certainly use command or process substitution to pass commands to an eval statement if you're so inclined.
This is rarely worth the trouble, IMHO. If you must pass data structures around in Bash, use a global variable--that's what they're for. If you don't want to do that for some reason, though, think in terms of positional parameters.
Your example could easily be rewritten to use positional parameters instead of global variables:
use_array () {
for idx in "$#"; do
echo "$idx"
done
}
create_array () {
local array=("a" "b" "c")
use_array "${array[#]}"
}
This all creates a certain amount of unnecessary complexity, though. Bash functions generally work best when you treat them more like procedures with side effects, and call them in sequence.
# Gather values and store them in FOO.
get_values_for_array () { :; }
# Do something with the values in FOO.
process_global_array_variable () { :; }
# Call your functions.
get_values_for_array
process_global_array_variable
If all you're worried about is polluting your global namespace, you can also use the unset builtin to remove a global variable after you're done with it. Using your original example, let my_list be global (by removing the local keyword) and add unset my_list to the end of my_algorithm to clean up after yourself.
You were not so far out with your original solution. You had a couple of problems, you used a comma as a separator, and you failed to capture the returned items into a list, try this:
my_algorithm() {
local result=( $(create_array) )
}
create_array() {
local my_list=("a" "b" "c")
echo "${my_list[#]}"
}
Considering the comments about embedded spaces, a few tweaks using IFS can solve that:
my_algorithm() {
oldIFS="$IFS"
IFS=','
local result=( $(create_array) )
IFS="$oldIFS"
echo "Should be 'c d': ${result[1]}"
}
create_array() {
IFS=','
local my_list=("a b" "c d" "e f")
echo "${my_list[*]}"
}
Use the technique developed by Matt McClure:
http://notes-matthewlmcclure.blogspot.com/2009/12/return-array-from-bash-function-v-2.html
Avoiding global variables means you can use the function in a pipe. Here is an example:
#!/bin/bash
makeJunk()
{
echo 'this is junk'
echo '#more junk and "b#d" characters!'
echo '!#$^%^&(*)_^&% ^$##:"<>?/.,\\"'"'"
}
processJunk()
{
local -a arr=()
# read each input and add it to arr
while read -r line
do
arr+=('"'"$line"'" is junk')
done;
# output the array as a string in the "declare" representation
declare -p arr | sed -e 's/^declare -a [^=]*=//'
}
# processJunk returns the array in a flattened string ready for "declare"
# Note that because of the pipe processJunk cannot return anything using
# a global variable
returned_string="$(makeJunk | processJunk)"
# convert the returned string to an array named returned_array
# declare correctly manages spaces and bad characters
eval "declare -a returned_array=${returned_string}"
for junk in "${returned_array[#]}"
do
echo "$junk"
done
Output is:
"this is junk" is junk
"#more junk and "b#d" characters!" is junk
"!#$^%^&(*)_^&% ^$##:"<>?/.,\\"'" is junk
A pure bash, minimal and robust solution based on the 'declare -p' builtin — without insane global variables
This approach involves the following three steps:
Convert the array with 'declare -p' and save the output in a variable.
myVar="$( declare -p myArray )"
The output of the declare -p statement can be used to recreate the array.
For instance the output of declare -p myVar might look like this:
declare -a myVar='([0]="1st field" [1]="2nd field" [2]="3rd field")'
Use the echo builtin to pass the variable to a function or to pass it back from there.
In order to preserve whitspaces in array fields when echoing the variable, IFS is temporarly set to a control character (e.g. a vertical tab).
Only the right-hand-side of the declare statement in the variable is to be echoed - this can be achieved by parameter expansion of the form ${parameter#word}. As for the example above: ${myVar#*=}
Finally, recreate the array where it is passed to using the eval and the 'declare -a' builtins.
Example 1 - return an array from a function
#!/bin/bash
# Example 1 - return an array from a function
function my-fun () {
# set up a new array with 3 fields - note the whitespaces in the
# 2nd (2 spaces) and 3rd (2 tabs) field
local myFunArray=( "1st field" "2nd field" "3rd field" )
# show its contents on stderr (must not be output to stdout!)
echo "now in $FUNCNAME () - showing contents of myFunArray" >&2
echo "by the help of the 'declare -p' builtin:" >&2
declare -p myFunArray >&2
# return the array
local myVar="$( declare -p myFunArray )"
local IFS=$'\v';
echo "${myVar#*=}"
# if the function would continue at this point, then IFS should be
# restored to its default value: <space><tab><newline>
IFS=' '$'\t'$'\n';
}
# main
# call the function and recreate the array that was originally
# set up in the function
eval declare -a myMainArray="$( my-fun )"
# show the array contents
echo ""
echo "now in main part of the script - showing contents of myMainArray"
echo "by the help of the 'declare -p' builtin:"
declare -p myMainArray
# end-of-file
Output of Example 1:
now in my-fun () - showing contents of myFunArray
by the help of the 'declare -p' builtin:
declare -a myFunArray='([0]="1st field" [1]="2nd field" [2]="3rd field")'
now in main part of the script - showing contents of myMainArray
by the help of the 'declare -p' builtin:
declare -a myMainArray='([0]="1st field" [1]="2nd field" [2]="3rd field")'
Example 2 - pass an array to a function
#!/bin/bash
# Example 2 - pass an array to a function
function my-fun () {
# recreate the array that was originally set up in the main part of
# the script
eval declare -a myFunArray="$( echo "$1" )"
# note that myFunArray is local - from the bash(1) man page: when used
# in a function, declare makes each name local, as with the local
# command, unless the ‘-g’ option is used.
# IFS has been changed in the main part of this script - now that we
# have recreated the array it's better to restore it to the its (local)
# default value: <space><tab><newline>
local IFS=' '$'\t'$'\n';
# show contents of the array
echo ""
echo "now in $FUNCNAME () - showing contents of myFunArray"
echo "by the help of the 'declare -p' builtin:"
declare -p myFunArray
}
# main
# set up a new array with 3 fields - note the whitespaces in the
# 2nd (2 spaces) and 3rd (2 tabs) field
myMainArray=( "1st field" "2nd field" "3rd field" )
# show the array contents
echo "now in the main part of the script - showing contents of myMainArray"
echo "by the help of the 'declare -p' builtin:"
declare -p myMainArray
# call the function and pass the array to it
myVar="$( declare -p myMainArray )"
IFS=$'\v';
my-fun $( echo "${myVar#*=}" )
# if the script would continue at this point, then IFS should be restored
# to its default value: <space><tab><newline>
IFS=' '$'\t'$'\n';
# end-of-file
Output of Example 2:
now in the main part of the script - showing contents of myMainArray
by the help of the 'declare -p' builtin:
declare -a myMainArray='([0]="1st field" [1]="2nd field" [2]="3rd field")'
now in my-fun () - showing contents of myFunArray
by the help of the 'declare -p' builtin:
declare -a myFunArray='([0]="1st field" [1]="2nd field" [2]="3rd field")'
I recently discovered a quirk in BASH in that a function has direct access to the variables declared in the functions higher in the call stack. I've only just started to contemplate how to exploit this feature (it promises both benefits and dangers), but one obvious application is a solution to the spirit of this problem.
I would also prefer to get a return value rather than using a global variable when delegating the creation of an array. There are several reasons for my preference, among which are to avoid possibly disturbing an preexisting value and to avoid leaving a value that may be invalid when later accessed. While there are workarounds to these problems, the easiest is have the variable go out of scope when the code is finished with it.
My solution ensures that the array is available when needed and discarded when the function returns, and leaves undisturbed a global variable with the same name.
#!/bin/bash
myarr=(global array elements)
get_an_array()
{
myarr=( $( date +"%Y %m %d" ) )
}
request_array()
{
declare -a myarr
get_an_array "myarr"
echo "New contents of local variable myarr:"
printf "%s\n" "${myarr[#]}"
}
echo "Original contents of global variable myarr:"
printf "%s\n" "${myarr[#]}"
echo
request_array
echo
echo "Confirm the global myarr was not touched:"
printf "%s\n" "${myarr[#]}"
Here is the output of this code:
When function request_array calls get_an_array, get_an_array can directly set the myarr variable that is local to request_array. Since myarr is created with declare, it is local to request_array and thus goes out of scope when request_array returns.
Although this solution does not literally return a value, I suggest that taken as a whole, it satisfies the promises of a true function return value.
Useful example: return an array from function
function Query() {
local _tmp=`echo -n "$*" | mysql 2>> zz.err`;
echo -e "$_tmp";
}
function StrToArray() {
IFS=$'\t'; set $1; for item; do echo $item; done; IFS=$oIFS;
}
sql="SELECT codi, bloc, requisit FROM requisits ORDER BY codi";
qry=$(Query $sql0);
IFS=$'\n';
for row in $qry; do
r=( $(StrToArray $row) );
echo ${r[0]} - ${r[1]} - ${r[2]};
done
I tried various implementations, and none preserved arrays that had elements with spaces ... because they all had to use echo.
# These implementations only work if no array items contain spaces.
use_array() { eval echo '(' \"\${${1}\[\#\]}\" ')'; }
use_array() { local _array="${1}[#]"; echo '(' "${!_array}" ')'; }
Solution
Then I came across Dennis Williamson's answer. I incorporated his method into the following functions so they can a) accept an arbitrary array and b) be used to pass, duplicate and append arrays.
# Print array definition to use with assignments, for loops, etc.
# varname: the name of an array variable.
use_array() {
local r=$( declare -p $1 )
r=${r#declare\ -a\ *=}
# Strip keys so printed definition will be a simple list (like when using
# "${array[#]}"). One side effect of having keys in the definition is
# that when appending arrays (i.e. `a1+=$( use_array a2 )`), values at
# matching indices merge instead of pushing all items onto array.
echo ${r//\[[0-9]\]=}
}
# Same as use_array() but preserves keys.
use_array_assoc() {
local r=$( declare -p $1 )
echo ${r#declare\ -a\ *=}
}
Then, other functions can return an array using catchable output or indirect arguments.
# catchable output
return_array_by_printing() {
local returnme=( "one" "two" "two and a half" )
use_array returnme
}
eval test1=$( return_array_by_printing )
# indirect argument
return_array_to_referenced_variable() {
local returnme=( "one" "two" "two and a half" )
eval $1=$( use_array returnme )
}
return_array_to_referenced_variable test2
# Now both test1 and test2 are arrays with three elements
I needed a similar functionality recently, so the following is a mix of the suggestions made by RashaMatt and Steve Zobell.
echo each array/list element as separate line from within a function
use mapfile to read all array/list elements echoed by a function.
As far as I can see, strings are kept intact and whitespaces are preserved.
#!bin/bash
function create-array() {
local somearray=("aaa" "bbb ccc" "d" "e f g h")
for elem in "${somearray[#]}"
do
echo "${elem}"
done
}
mapfile -t resa <<< "$(create-array)"
# quick output check
declare -p resa
Some more variations…
#!/bin/bash
function create-array-from-ls() {
local somearray=("$(ls -1)")
for elem in "${somearray[#]}"
do
echo "${elem}"
done
}
function create-array-from-args() {
local somearray=("$#")
for elem in "${somearray[#]}"
do
echo "${elem}"
done
}
mapfile -t resb <<< "$(create-array-from-ls)"
mapfile -t resc <<< "$(create-array-from-args 'xxx' 'yy zz' 't s u' )"
sentenceA="create array from this sentence"
sentenceB="keep this sentence"
mapfile -t resd <<< "$(create-array-from-args ${sentenceA} )"
mapfile -t rese <<< "$(create-array-from-args "$sentenceB" )"
mapfile -t resf <<< "$(create-array-from-args "$sentenceB" "and" "this words" )"
# quick output check
declare -p resb
declare -p resc
declare -p resd
declare -p rese
declare -p resf
Here is a solution with no external array references and no IFS manipulation:
# add one level of single quotes to args, eval to remove
squote () {
local a=("$#")
a=("${a[#]//\'/\'\\\'\'}") # "'" => "'\''"
a=("${a[#]/#/\'}") # add "'" prefix to each word
a=("${a[#]/%/\'}") # add "'" suffix to each word
echo "${a[#]}"
}
create_array () {
local my_list=(a "b 'c'" "\\\"d
")
squote "${my_list[#]}"
}
my_algorithm () {
eval "local result=($(create_array))"
# result=([0]="a" [1]="b 'c'" [2]=$'\\"d\n')
}
[Note: the following was rejected as an edit of this answer for reasons that make no sense to me (since the edit was not intended to address the author of the post!), so I'm taking the suggestion to make it a separate answer.]
A simpler implementation of Steve Zobell's adaptation of Matt McClure's technique uses the bash built-in (since version == 4) readarray as suggested by RastaMatt to create a representation of an array that can be converted into an array at runtime. (Note that both readarray and mapfile name the same code.) It still avoids globals (allowing use of the function in a pipe), and still handles nasty characters.
For some more-fully-developed (e.g., more modularization) but still-kinda-toy examples, see bash_pass_arrays_between_functions. Following are a few easily-executable examples, provided here to avoid moderators b!tching about external links.
Cut the following block and paste it into a bash terminal to create /tmp/source.sh and /tmp/junk1.sh:
FP='/tmp/source.sh' # path to file to be created for `source`ing
cat << 'EOF' > "${FP}" # suppress interpretation of variables in heredoc
function make_junk {
echo 'this is junk'
echo '#more junk and "b#d" characters!'
echo '!#$^%^&(*)_^&% ^$##:"<>?/.,\\"'"'"
}
### Use 'readarray' (aka 'mapfile', bash built-in) to read lines into an array.
### Handles blank lines, whitespace and even nastier characters.
function lines_to_array_representation {
local -a arr=()
readarray -t arr
# output array as string using 'declare's representation (minus header)
declare -p arr | sed -e 's/^declare -a [^=]*=//'
}
EOF
FP1='/tmp/junk1.sh' # path to script to run
cat << 'EOF' > "${FP1}" # suppress interpretation of variables in heredoc
#!/usr/bin/env bash
source '/tmp/source.sh' # to reuse its functions
returned_string="$(make_junk | lines_to_array_representation)"
eval "declare -a returned_array=${returned_string}"
for elem in "${returned_array[#]}" ; do
echo "${elem}"
done
EOF
chmod u+x "${FP1}"
# newline here ... just hit Enter ...
Run /tmp/junk1.sh: output should be
this is junk
#more junk and "b#d" characters!
!#$^%^&(*)_^&% ^$##:"<>?/.,\\"'
Note lines_to_array_representation also handles blank lines. Try pasting the following block into your bash terminal:
FP2='/tmp/junk2.sh' # path to script to run
cat << 'EOF' > "${FP2}" # suppress interpretation of variables in heredoc
#!/usr/bin/env bash
source '/tmp/source.sh' # to reuse its functions
echo '`bash --version` the normal way:'
echo '--------------------------------'
bash --version
echo # newline
echo '`bash --version` via `lines_to_array_representation`:'
echo '-----------------------------------------------------'
bash_version="$(bash --version | lines_to_array_representation)"
eval "declare -a returned_array=${bash_version}"
for elem in "${returned_array[#]}" ; do
echo "${elem}"
done
echo # newline
echo 'But are they *really* the same? Ask `diff`:'
echo '-------------------------------------------'
echo 'You already know how to capture normal output (from `bash --version`):'
declare -r PATH_TO_NORMAL_OUTPUT="$(mktemp)"
bash --version > "${PATH_TO_NORMAL_OUTPUT}"
echo "normal output captured to file # ${PATH_TO_NORMAL_OUTPUT}"
ls -al "${PATH_TO_NORMAL_OUTPUT}"
echo # newline
echo 'Capturing L2AR takes a bit more work, but is not onerous.'
echo "Look # contents of the file you're about to run to see how it's done."
declare -r RAW_L2AR_OUTPUT="$(bash --version | lines_to_array_representation)"
declare -r PATH_TO_COOKED_L2AR_OUTPUT="$(mktemp)"
eval "declare -a returned_array=${RAW_L2AR_OUTPUT}"
for elem in "${returned_array[#]}" ; do
echo "${elem}" >> "${PATH_TO_COOKED_L2AR_OUTPUT}"
done
echo "output from lines_to_array_representation captured to file # ${PATH_TO_COOKED_L2AR_OUTPUT}"
ls -al "${PATH_TO_COOKED_L2AR_OUTPUT}"
echo # newline
echo 'So are they really the same? Per'
echo "\`diff -uwB "${PATH_TO_NORMAL_OUTPUT}" "${PATH_TO_COOKED_L2AR_OUTPUT}" | wc -l\`"
diff -uwB "${PATH_TO_NORMAL_OUTPUT}" "${PATH_TO_COOKED_L2AR_OUTPUT}" | wc -l
echo '... they are the same!'
EOF
chmod u+x "${FP2}"
# newline here ... just hit Enter ...
Run /tmp/junk2.sh # commandline. Your output should be similar to mine:
`bash --version` the normal way:
--------------------------------
GNU bash, version 4.3.30(1)-release (x86_64-pc-linux-gnu)
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
`bash --version` via `lines_to_array_representation`:
-----------------------------------------------------
GNU bash, version 4.3.30(1)-release (x86_64-pc-linux-gnu)
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
But are they *really* the same? Ask `diff`:
-------------------------------------------
You already know how to capture normal output (from `bash --version`):
normal output captured to file # /tmp/tmp.Ni1bgyPPEw
-rw------- 1 me me 308 Jun 18 16:27 /tmp/tmp.Ni1bgyPPEw
Capturing L2AR takes a bit more work, but is not onerous.
Look # contents of the file you're about to run to see how it's done.
output from lines_to_array_representation captured to file # /tmp/tmp.1D6O2vckGz
-rw------- 1 me me 308 Jun 18 16:27 /tmp/tmp.1D6O2vckGz
So are they really the same? Per
`diff -uwB /tmp/tmp.Ni1bgyPPEw /tmp/tmp.1D6O2vckGz | wc -l`
0
... they are the same!
There's no need to use eval or to change IFS to \n. There are at least 2 good ways to do this.
1) Using echo and mapfile
You can simply echo each item of the array in the function, then use mapfile to turn it into an array:
outputArray()
{
for i
{
echo "$i"
}
}
declare -a arr=( 'qq' 'www' 'ee rr' )
mapfile -t array < <(outputArray "${arr[#]}")
for i in "${array[#]}"
do
echo "i=$i"
done
To make it work using pipes, add (( $# == 0 )) && readarray -t temp && set "${temp[#]}" && unset temp to the top of output array. It converts stdin to parameters.
2) Using declare -p and sed
This can also be done using declare -p and sed instead of mapfile.
outputArray()
{
(( $# == 0 )) && readarray -t temp && set "${temp[#]}" && unset temp
for i; { echo "$i"; }
}
returnArray()
{
local -a arr=()
(( $# == 0 )) && readarray -t arr || for i; { arr+=("$i"); }
declare -p arr | sed -e 's/^declare -a [^=]*=//'
}
declare -a arr=( 'qq' 'www' 'ee rr' )
declare -a array=$(returnArray "${arr[#]}")
for i in "${array[#]}"
do
echo "i=$i"
done
declare -a array=$(outputArray "${arr[#]}" | returnArray)
echo
for i in "${array[#]}"
do
echo "i=$i"
done
declare -a array < <(outputArray "${arr[#]}" | returnArray)
echo
for i in "${array[#]}"
do
echo "i=$i"
done
This can also be done by simply passing array variable to the function and assign array values to this var then use this var outside of function. For example.
create_array() {
local __resultArgArray=$1
local my_list=("a" "b" "c")
eval $__resultArgArray="("${my_list[#]}")"
}
my_algorithm() {
create_array result
echo "Total elements in the array: ${#result[#]}"
for i in "${result[#]}"
do
echo $i
done
}
my_algorithm
The easest way y found
my_function()
{
array=(one two three)
echo ${array[#]}
}
result=($(my_function))
echo ${result[0]}
echo ${result[1]}
echo ${result[2]}
You can also use the declare -p method more easily by taking advantage of declare -a's double-evaluation when the value is a string (no true parens outside the string):
# return_array_value returns the value of array whose name is passed in.
# It turns the array into a declaration statement, then echos the value
# part of that statement with parentheses intact. You can use that
# result in a "declare -a" statement to create your own array with the
# same value. Also works for associative arrays with "declare -A".
return_array_value () {
declare Array_name=$1 # namespace locals with caps to prevent name collision
declare Result
Result=$(declare -p $Array_name) # dehydrate the array into a declaration
echo "${Result#*=}" # trim "declare -a ...=" from the front
}
# now use it. test for robustness by skipping an index and putting a
# space in an entry.
declare -a src=([0]=one [2]="two three")
declare -a dst="$(return_array_value src)" # rehydrate with double-eval
declare -p dst
> declare -a dst=([0]="one" [2]="two three") # result matches original
Verifying the result, declare -p dst yields declare -a dst=([0]="one" [2]="two three")", demonstrating that this method correctly deals with both sparse arrays as well as entries with an IFS character (space).
The first thing is to dehydrate the source array by using declare -p to generate a valid bash declaration of it. Because the declaration is a full statement, including "declare" and the variable name, we strip that part from the front with ${Result#*=}, leaving the parentheses with the indices and values inside: ([0]="one" [2]="two three").
It then rehydrates the array by feeding that value to your own declare statement, one where you choose the array name. It relies on the fact that the right side of the dst array declaration is a string with parentheses that are inside the string, rather than true parentheses in the declare itself, e.g. not declare -a dst=( "true parens outside string" ). This triggers declare to evaluate the string twice, once into a valid statement with parentheses (and quotes in the value preserved), and another for the actual assignment. I.e. it evaluates first to declare -a dst=([0]="one" [2]="two three"), then evaluates that as a statement.
Note that this double evaluation behavior is specific to the -a and -A options of declare.
Oh, and this method works with associative arrays as well, just change -a to -A.
Because this method relies on stdout, it works across subshell boundaries like pipelines, as others have noted.
I discuss this method in more detail in my blog post
If your source data is formatted with each list element on a separate line, then the mapfile builtin is a simple and elegant way to read a list into an array:
$ list=$(ls -1 /usr/local) # one item per line
$ mapfile -t arrayVar <<<"$list" # -t trims trailing newlines
$ declare -p arrayVar | sed 's#\[#\n[#g'
declare -a arrayVar='(
[0]="bin"
[1]="etc"
[2]="games"
[3]="include"
[4]="lib"
[5]="man"
[6]="sbin"
[7]="share"
[8]="src")'
Note that, as with the read builtin, you would not ordinarily* use mapfile in a pipeline (or subshell) because the assigned array variable would be unavailable to subsequent statements (* unless bash job control is disabled and shopt -s lastpipe is set).
$ help mapfile
mapfile: mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
Read lines from the standard input into an indexed array variable.
Read lines from the standard input into the indexed array variable ARRAY, or
from file descriptor FD if the -u option is supplied. The variable MAPFILE
is the default ARRAY.
Options:
-n count Copy at most COUNT lines. If COUNT is 0, all lines are copied.
-O origin Begin assigning to ARRAY at index ORIGIN. The default index is 0.
-s count Discard the first COUNT lines read.
-t Remove a trailing newline from each line read.
-u fd Read lines from file descriptor FD instead of the standard input.
-C callback Evaluate CALLBACK each time QUANTUM lines are read.
-c quantum Specify the number of lines read between each call to CALLBACK.
Arguments:
ARRAY Array variable name to use for file data.
If -C is supplied without -c, the default quantum is 5000. When
CALLBACK is evaluated, it is supplied the index of the next array
element to be assigned and the line to be assigned to that element
as additional arguments.
If not supplied with an explicit origin, mapfile will clear ARRAY before
assigning to it.
Exit Status:
Returns success unless an invalid option is given or ARRAY is readonly or
not an indexed array.
You can try this
my_algorithm() {
create_array list
for element in "${list[#]}"
do
echo "${element}"
done
}
create_array() {
local my_list=("1st one" "2nd two" "3rd three")
eval "${1}=()"
for element in "${my_list[#]}"
do
eval "${1}+=(\"${element}\")"
done
}
my_algorithm
The output is
1st one
2nd two
3rd three
I'd suggest piping to a code block to set values of an array. The strategy is POSIX compatible, so you get both Bash and Zsh, and doesn't run the risk of side effects like the posted solutions.
i=0 # index for our new array
declare -a arr # our new array
# pipe from a function that produces output by line
ls -l | { while read data; do i=$i+1; arr[$i]="$data"; done }
# example of reading that new array
for row in "${arr[#]}"; do echo "$row"; done
This will work for zsh and bash, and won't be affected by spaces or special characters. In the case of the OP, the output is transformed by echo, so it is not actually outputting an array, but printing it (as others mentioned shell functions return status not values). We can change it to a pipeline ready mechanism:
create_array() {
local my_list=("a", "b", "c")
for row in "${my_list[#]}"; do
echo "$row"
done
}
my_algorithm() {
i=0
declare -a result
create_array | { while read data; do i=$i+1; result[$i]="$data"; done }
}
If so inclined, one could remove the create_array pipeline process from my_algorithm and chain the two functions together
create_array | my_algorithm
A modern Bash implementation using #Q to safely output array elements:
#!/usr/bin/env bash
return_array_elements() {
local -a foo_array=('1st one' '2nd two' '3rd three')
printf '%s\n' "${foo_array[#]#Q}"
}
use_array_elements() {
local -a bar_array="($(return_array_elements))"
# Display declareation of bar_array
# which is local to this function, but whose elements
# hahaves been returned by the return_array_elements function
declare -p bar_array
}
use_array_elements
Output:
declare -a bar_array=([0]="1st one" [1]="2nd two" [2]="3rd three")
While the declare -p approach is elegant indeed, you can still create a global array using declare -g within a function and have it visible outside the scope of the function:
create_array() {
declare -ag result=("a", "b", "c")
}
my_algorithm() {
create_array
echo "${result[#]}"
}
How can I pass an array as parameter to a bash function?
Note: After not finding an answer here on Stack Overflow, I posted my somewhat crude solution myself. It allows for only one array being passed, and it being the last element of the parameter list. Actually, it is not passing the array at all, but a list of its elements, which are re-assembled into an array by called_function(), but it worked for me. If someone knows a better way, feel free to add it here.
You can pass multiple arrays as arguments using something like this:
takes_ary_as_arg()
{
declare -a argAry1=("${!1}")
echo "${argAry1[#]}"
declare -a argAry2=("${!2}")
echo "${argAry2[#]}"
}
try_with_local_arys()
{
# array variables could have local scope
local descTable=(
"sli4-iread"
"sli4-iwrite"
"sli3-iread"
"sli3-iwrite"
)
local optsTable=(
"--msix --iread"
"--msix --iwrite"
"--msi --iread"
"--msi --iwrite"
)
takes_ary_as_arg descTable[#] optsTable[#]
}
try_with_local_arys
will echo:
sli4-iread sli4-iwrite sli3-iread sli3-iwrite
--msix --iread --msix --iwrite --msi --iread --msi --iwrite
Edit/notes: (from comments below)
descTable and optsTable are passed as names and are expanded in the function. Thus no $ is needed when given as parameters.
Note that this still works even with descTable etc being defined with local, because locals are visible to the functions they call.
The ! in ${!1} expands the arg 1 variable.
declare -a just makes the indexed array explicit, it is not strictly necessary.
Note: This is the somewhat crude solution I posted myself, after not finding an answer here on Stack Overflow. It allows for only one array being passed, and it being the last element of the parameter list. Actually, it is not passing the array at all, but a list of its elements, which are re-assembled into an array by called_function(), but it worked for me. Somewhat later Ken posted his solution, but I kept mine here for "historic" reference.
calling_function()
{
variable="a"
array=( "x", "y", "z" )
called_function "${variable}" "${array[#]}"
}
called_function()
{
local_variable="${1}"
shift
local_array=("${#}")
}
Commenting on Ken Bertelson solution and answering Jan Hettich:
How it works
the takes_ary_as_arg descTable[#] optsTable[#] line in try_with_local_arys() function sends:
This is actually creates a copy of the descTable and optsTable arrays which are accessible to the takes_ary_as_arg function.
takes_ary_as_arg() function receives descTable[#] and optsTable[#] as strings, that means $1 == descTable[#] and $2 == optsTable[#].
in the beginning of takes_ary_as_arg() function it uses ${!parameter} syntax, which is called indirect reference or sometimes double referenced, this means that instead of using $1's value, we use the value of the expanded value of $1, example:
baba=booba
variable=baba
echo ${variable} # baba
echo ${!variable} # booba
likewise for $2.
putting this in argAry1=("${!1}") creates argAry1 as an array (the brackets following =) with the expanded descTable[#], just like writing there argAry1=("${descTable[#]}") directly.
the declare there is not required.
N.B.: It is worth mentioning that array initialization using this bracket form initializes the new array according to the IFS or Internal Field Separator which is by default tab, newline and space. in that case, since it used [#] notation each element is seen by itself as if he was quoted (contrary to [*]).
My reservation with it
In BASH, local variable scope is the current function and every child function called from it, this translates to the fact that takes_ary_as_arg() function "sees" those descTable[#] and optsTable[#] arrays, thus it is working (see above explanation).
Being that case, why not directly look at those variables themselves? It is just like writing there:
argAry1=("${descTable[#]}")
See above explanation, which just copies descTable[#] array's values according to the current IFS.
In summary
This is passing, in essence, nothing by value - as usual.
I also want to emphasize Dennis Williamson comment above: sparse arrays (arrays without all the keys defines - with "holes" in them) will not work as expected - we would loose the keys and "condense" the array.
That being said, I do see the value for generalization, functions thus can get the arrays (or copies) without knowing the names:
for ~"copies": this technique is good enough, just need to keep aware, that the indices (keys) are gone.
for real copies:
we can use an eval for the keys, for example:
eval local keys=(\${!$1})
and then a loop using them to create a copy.
Note: here ! is not used it's previous indirect/double evaluation, but rather in array context it returns the array indices (keys).
and, of course, if we were to pass descTable and optsTable strings (without [#]), we could use the array itself (as in by reference) with eval. for a generic function that accepts arrays.
The basic problem here is that the bash developer(s) that designed/implemented arrays really screwed the pooch. They decided that ${array} was just short hand for ${array[0]}, which was a bad mistake. Especially when you consider that ${array[0]} has no meaning and evaluates to the empty string if the array type is associative.
Assigning an array takes the form array=(value1 ... valueN) where value has the syntax [subscript]=string, thereby assigning a value directly to a particular index in the array. This makes it so there can be two types of arrays, numerically indexed and hash indexed (called associative arrays in bash parlance). It also makes it so that you can create sparse numerically indexed arrays. Leaving off the [subscript]= part is short hand for a numerically indexed array, starting with the ordinal index of 0 and incrementing with each new value in the assignment statement.
Therefore, ${array} should evaluate to the entire array, indexes and all. It should evaluate to the inverse of the assignment statement. Any third year CS major should know that. In that case, this code would work exactly as you might expect it to:
declare -A foo bar
foo=${bar}
Then, passing arrays by value to functions and assigning one array to another would work as the rest of the shell syntax dictates. But because they didn't do this right, the assignment operator = doesn't work for arrays, and arrays can't be passed by value to functions or to subshells or output in general (echo ${array}) without code to chew through it all.
So, if it had been done right, then the following example would show how the usefulness of arrays in bash could be substantially better:
simple=(first=one second=2 third=3)
echo ${simple}
the resulting output should be:
(first=one second=2 third=3)
Then, arrays could use the assignment operator, and be passed by value to functions and even other shell scripts. Easily stored by outputting to a file, and easily loaded from a file into a script.
declare -A foo
read foo <file
Alas, we have been let down by an otherwise superlative bash development team.
As such, to pass an array to a function, there is really only one option, and that is to use the nameref feature:
function funky() {
local -n ARR
ARR=$1
echo "indexes: ${!ARR[#]}"
echo "values: ${ARR[#]}"
}
declare -A HASH
HASH=([foo]=bar [zoom]=fast)
funky HASH # notice that I'm just passing the word 'HASH' to the function
will result in the following output:
indexes: foo zoom
values: bar fast
Since this is passing by reference, you can also assign to the array in the function. Yes, the array being referenced has to have a global scope, but that shouldn't be too big a deal, considering that this is shell scripting. To pass an associative or sparse indexed array by value to a function requires throwing all the indexes and the values onto the argument list (not too useful if it's a large array) as single strings like this:
funky "${!array[*]}" "${array[*]}"
and then writing a bunch of code inside the function to reassemble the array.
DevSolar's answer has one point I don't understand (maybe he has a specific reason to do so, but I can't think of one): He sets the array from the positional parameters element by element, iterative.
An easier approuch would be
called_function()
{
...
# do everything like shown by DevSolar
...
# now get a copy of the positional parameters
local_array=("$#")
...
}
An easy way to pass several arrays as parameter is to use a character-separated string. You can call your script like this:
./myScript.sh "value1;value2;value3" "somethingElse" "value4;value5" "anotherOne"
Then, you can extract it in your code like this:
myArray=$1
IFS=';' read -a myArray <<< "$myArray"
myOtherArray=$3
IFS=';' read -a myOtherArray <<< "$myOtherArray"
This way, you can actually pass multiple arrays as parameters and it doesn't have to be the last parameters.
function aecho {
set "$1[$2]"
echo "${!1}"
}
Example
$ foo=(dog cat bird)
$ aecho foo 1
cat
Modern bash (apparently version 4.3 or later), allows you to pass arrays by reference. I'll show that below. If you'd like to manually serialize and deserialize the arrays instead, see my answer here for bash regular "indexed" arrays, and here for bash associative arrays. Passing arrays by reference, as shown below, is much easier and more-concise, however, so that's what I now recommend.
The code below is also available online in my eRCaGuy_hello_world repo here: array_pass_as_bash_parameter_by_reference.sh. See also this example here: array_pass_as_bash_parameter_2_associative.sh.
Here is a demo for regular bash arrays:
function foo {
# declare a local **reference variable** (hence `-n`) named `data_ref`
# which is a reference to the value stored in the first parameter
# passed in
local -n data_ref="$1"
echo "${data_ref[0]}"
echo "${data_ref[1]}"
}
# declare a regular bash "indexed" array
declare -a data
data+=("Fred Flintstone")
data+=("Barney Rubble")
foo "data"
Sample output:
Fred Flintstone
Barney Rubble
...and here is a demo for associative bash arrays (ie: bash hash tables, "dictionaries", or "unordered maps"):
function foo {
# declare a local **reference variable** (hence `-n`) named `data_ref`
# which is a reference to the value stored in the first parameter
# passed in
local -n data_ref="$1"
echo "${data_ref["a"]}"
echo "${data_ref["b"]}"
}
# declare a bash associative array
declare -A data
data["a"]="Fred Flintstone"
data["b"]="Barney Rubble"
foo "data"
Sample output:
Fred Flintstone
Barney Rubble
References:
I modified the above code samples from #Todd Lehman's answer here: How to pass an associative array as argument to a function in Bash?
See also my manual serializing/deserializing answer here
And see my follow-up Question here: Why do the man bash pages state the declare and local -n attribute "cannot be applied to array variables", and yet it can?
This one works even with spaces:
format="\t%2s - %s\n"
function doAction
{
local_array=("$#")
for (( i = 0 ; i < ${#local_array[#]} ; i++ ))
do
printf "${format}" $i "${local_array[$i]}"
done
echo -n "Choose: "
option=""
read -n1 option
echo ${local_array[option]}
return
}
#the call:
doAction "${tools[#]}"
With a few tricks you can actually pass named parameters to functions, along with arrays.
The method I developed allows you to access parameters passed to a function like this:
testPassingParams() {
#var hello
l=4 #array anArrayWithFourElements
l=2 #array anotherArrayWithTwo
#var anotherSingle
#reference table # references only work in bash >=4.3
#params anArrayOfVariedSize
test "$hello" = "$1" && echo correct
#
test "${anArrayWithFourElements[0]}" = "$2" && echo correct
test "${anArrayWithFourElements[1]}" = "$3" && echo correct
test "${anArrayWithFourElements[2]}" = "$4" && echo correct
# etc...
#
test "${anotherArrayWithTwo[0]}" = "$6" && echo correct
test "${anotherArrayWithTwo[1]}" = "$7" && echo correct
#
test "$anotherSingle" = "$8" && echo correct
#
test "${table[test]}" = "works"
table[inside]="adding a new value"
#
# I'm using * just in this example:
test "${anArrayOfVariedSize[*]}" = "${*:10}" && echo correct
}
fourElements=( a1 a2 "a3 with spaces" a4 )
twoElements=( b1 b2 )
declare -A assocArray
assocArray[test]="works"
testPassingParams "first" "${fourElements[#]}" "${twoElements[#]}" "single with spaces" assocArray "and more... " "even more..."
test "${assocArray[inside]}" = "adding a new value"
In other words, not only you can call your parameters by their names (which makes up for a more readable core), you can actually pass arrays (and references to variables - this feature works only in bash 4.3 though)! Plus, the mapped variables are all in the local scope, just as $1 (and others).
The code that makes this work is pretty light and works both in bash 3 and bash 4 (these are the only versions I've tested it with). If you're interested in more tricks like this that make developing with bash much nicer and easier, you can take a look at my Bash Infinity Framework, the code below was developed for that purpose.
Function.AssignParamLocally() {
local commandWithArgs=( $1 )
local command="${commandWithArgs[0]}"
shift
if [[ "$command" == "trap" || "$command" == "l="* || "$command" == "_type="* ]]
then
paramNo+=-1
return 0
fi
if [[ "$command" != "local" ]]
then
assignNormalCodeStarted=true
fi
local varDeclaration="${commandWithArgs[1]}"
if [[ $varDeclaration == '-n' ]]
then
varDeclaration="${commandWithArgs[2]}"
fi
local varName="${varDeclaration%%=*}"
# var value is only important if making an object later on from it
local varValue="${varDeclaration#*=}"
if [[ ! -z $assignVarType ]]
then
local previousParamNo=$(expr $paramNo - 1)
if [[ "$assignVarType" == "array" ]]
then
# passing array:
execute="$assignVarName=( \"\${#:$previousParamNo:$assignArrLength}\" )"
eval "$execute"
paramNo+=$(expr $assignArrLength - 1)
unset assignArrLength
elif [[ "$assignVarType" == "params" ]]
then
execute="$assignVarName=( \"\${#:$previousParamNo}\" )"
eval "$execute"
elif [[ "$assignVarType" == "reference" ]]
then
execute="$assignVarName=\"\$$previousParamNo\""
eval "$execute"
elif [[ ! -z "${!previousParamNo}" ]]
then
execute="$assignVarName=\"\$$previousParamNo\""
eval "$execute"
fi
fi
assignVarType="$__capture_type"
assignVarName="$varName"
assignArrLength="$__capture_arrLength"
}
Function.CaptureParams() {
__capture_type="$_type"
__capture_arrLength="$l"
}
alias #trapAssign='Function.CaptureParams; trap "declare -i \"paramNo+=1\"; Function.AssignParamLocally \"\$BASH_COMMAND\" \"\$#\"; [[ \$assignNormalCodeStarted = true ]] && trap - DEBUG && unset assignVarType && unset assignVarName && unset assignNormalCodeStarted && unset paramNo" DEBUG; '
alias #param='#trapAssign local'
alias #reference='_type=reference #trapAssign local -n'
alias #var='_type=var #param'
alias #params='_type=params #param'
alias #array='_type=array #param'
Just to add to the accepted answer, as I found it doesn't work well if the array contents are someting like:
RUN_COMMANDS=(
"command1 param1... paramN"
"command2 param1... paramN"
)
In this case, each member of the array gets split, so the array the function sees is equivalent to:
RUN_COMMANDS=(
"command1"
"param1"
...
"command2"
...
)
To get this case to work, the way I found is to pass the variable name to the function, then use eval:
function () {
eval 'COMMANDS=( "${'"$1"'[#]}" )'
for COMMAND in "${COMMANDS[#]}"; do
echo $COMMAND
done
}
function RUN_COMMANDS
Just my 2©
As ugly as it is, here is a workaround that works as long as you aren't passing an array explicitly, but a variable corresponding to an array:
function passarray()
{
eval array_internally=("$(echo '${'$1'[#]}')")
# access array now via array_internally
echo "${array_internally[#]}"
#...
}
array=(0 1 2 3 4 5)
passarray array # echo's (0 1 2 3 4 5) as expected
I'm sure someone can come up with a clearner implementation of the idea, but I've found this to be a better solution than passing an array as "{array[#]"} and then accessing it internally using array_inside=("$#"). This becomes complicated when there are other positional/getopts parameters. In these cases, I've had to first determine and then remove the parameters not associated with the array using some combination of shift and array element removal.
A purist perspective likely views this approach as a violation of the language, but pragmatically speaking, this approach has saved me a whole lot of grief. On a related topic, I also use eval to assign an internally constructed array to a variable named according to a parameter target_varname I pass to the function:
eval $target_varname=$"(${array_inside[#]})"
Hope this helps someone.
My short answer is:
function display_two_array {
local arr1=$1
local arr2=$2
for i in $arr1
do
echo "arrary1: $i"
done
for i in $arr2
do
echo "arrary2: $i"
done
}
test_array=(1 2 3 4 5)
test_array2=(7 8 9 10 11)
display_two_array "${test_array[*]}" "${test_array2[*]}"
It should be noticed that the ${test_array[*]} and ${test_array2[*]} should be surrounded by "", otherwise you'll fail.
The answer below shows you how to pass bash regular "indexed" arrays as parameters to a function essentially by serializing and deserializing them.
To see this manual serializing/deserializing for bash associative arrays (hash tables) instead of for regular indexed arrays, see my answer here.
For a better way (which requires bash version 4.3 or later, I think), which passes the arrays by reference, see the link just above and my other answer here.
Passing arrays by reference is much easier and more-concise, so that's what I now recommend. That being said, the manual serializing/deserializing techniques I show below are also extremely informative and useful.
Quick summary:
See the 3 separate function definitions below. I go over how to pass:
one bash array to a function
two or more bash arrays to a function, and
two or more bash arrays plus additional arguments (before or after the arrays) to a function.
12 years later and I still don't see any answers I really like here and which I would consider to be thorough enough, simple enough, and "canonical" enough for me to just use--answers which I can come back to again and again and copy and paste and expand when needed. So, here is my answer which I do consider to be all of these things.
How to pass bash arrays as parameters to bash functions
You might also call this "variadic argument parsing in bash functions or scripts", especially since the number of elements in each array passed in to the examples below can dynamically vary, and in bash the elements of an array essentially get passed to the function as separate input parameters even when the array is passed in via a single array expansion argument like this "${array1[#]}".
For all example code below, assume you have these two bash arrays for testing:
array1=()
array1+=("one")
array1+=("two")
array1+=("three")
array2=("four" "five" "six" "seven" "eight")
The code above and below is available in my bash/array_pass_as_bash_parameter.sh file in my eRCaGuy_hello_world repo on GitHub.
Example 1: how to pass one bash array to a function
To pass an array to a bash function, you have to pass all of its elements separately. Given bash array array1, the syntax to obtain all elements of this array is "${array1[#]}". Since all incoming parameters to a bash function or executable file get wrapped up in the magic bash input parameter array called #, you can read all members of the input array with the "$#" syntax, as shown below.
Function definition:
# Print all elements of a bash array.
# General form:
# print_one_array array1
# Example usage:
# print_one_array "${array1[#]}"
print_one_array() {
for element in "$#"; do
printf " %s\n" "$element"
done
}
Example usage:
echo "Printing array1"
# This syntax passes all members of array1 as separate input arguments to
# the function
print_one_array "${array1[#]}"
Example Output:
Printing array1
one
two
three
Example 2: how to pass two or more bash arrays to a function...
(and how to recapture the input arrays as separate bash arrays again)
Here, we need to differentiate which incoming parameters belong to which array. To do this, we need to know the size of each array, meaning the number of elements in each array. This is very similar to passing arrays in C, where we also generally must know the array length passed to any C function. Given bash array array1, the number of elements in it can be obtained with "${#array1[#]}" (notice the usage of the # symbol). In order to know where in the input arguments the array_len length parameter is, we must always pass the array length parameter for each array before passing the individual array elements, as shown below.
In order to parse the arrays, I use array slicing on the input argument array, #.
Here is a reminder on how bash array slicing syntax works (from my answer here). In the slicing syntax :start:length, the 1st number is the zero-based index to start slicing from, and the 2nd number is the number of elements to grab:
# array slicing basic format 1: grab a certain length starting at a certain
# index
echo "${#:2:5}"
# │ │
# │ └────> slice length
# └──────> slice starting index (zero-based)
# array slicing basic format 2: grab all remaining array elements starting at a
# certain index through to the end
echo "${#:2}"
# │
# │
# └──────> slice starting index (zero-based)
Also, in order to force the sliced parameters from the input array to become a new array, I surround them in parenthesis (), like this, for example ("${#:$i:$array1_len}"). Those parenthesis on the outside are important, again, because that's how we make an array in bash.
This example below only accepts two bash arrays, but following the given patterns it can be easily adapted to accept any number of bash arrays as arguments.
Function definition:
# Print all elements of two bash arrays.
# General form (notice length MUST come before the array in order
# to be able to parse the args!):
# print_two_arrays array1_len array1 array2_len array2
# Example usage:
# print_two_arrays "${#array1[#]}" "${array1[#]}" \
# "${#array2[#]}" "${array2[#]}"
print_two_arrays() {
# For debugging: print all input args
echo "All args to 'print_two_arrays':"
print_one_array "$#"
i=1
# Read array1_len into a variable
array1_len="${#:$i:1}"
((i++))
# Read array1 into a new array
array1=("${#:$i:$array1_len}")
((i += $array1_len))
# Read array2_len into a variable
array2_len="${#:$i:1}"
((i++))
# Read array2 into a new array
array2=("${#:$i:$array2_len}")
((i += $array2_len))
# Print the two arrays
echo "array1:"
print_one_array "${array1[#]}"
echo "array2:"
print_one_array "${array2[#]}"
}
Example usage:
echo "Printing array1 and array2"
print_two_arrays "${#array1[#]}" "${array1[#]}" "${#array2[#]}" "${array2[#]}"
Example Output:
Printing array1 and array2
All args to 'print_two_arrays':
3
one
two
three
5
four
five
six
seven
eight
array1:
one
two
three
array2:
four
five
six
seven
eight
Example 3: pass two bash arrays plus some extra args after that to a function
This is a tiny expansion of the example above. It also uses bash array slicing, just like the example above. Instead of stopping after parsing two full input arrays, however, we continue and parse a couple more arguments at the end. This pattern can be continued indefinitely for any number of bash arrays and any number of additional arguments, accommodating any input argument order, so long as the length of each bash array comes just before the elements of that array.
Function definition:
# Print all elements of two bash arrays, plus two extra args at the end.
# General form (notice length MUST come before the array in order
# to be able to parse the args!):
# print_two_arrays_plus_extra_args array1_len array1 array2_len array2 \
# extra_arg1 extra_arg2
# Example usage:
# print_two_arrays_plus_extra_args "${#array1[#]}" "${array1[#]}" \
# "${#array2[#]}" "${array2[#]}" "hello" "world"
print_two_arrays_plus_extra_args() {
i=1
# Read array1_len into a variable
array1_len="${#:$i:1}"
((i++))
# Read array1 into a new array
array1=("${#:$i:$array1_len}")
((i += $array1_len))
# Read array2_len into a variable
array2_len="${#:$i:1}"
((i++))
# Read array2 into a new array
array2=("${#:$i:$array2_len}")
((i += $array2_len))
# You can now read the extra arguments all at once and gather them into a
# new array like this:
extra_args_array=("${#:$i}")
# OR you can read the extra arguments individually into their own variables
# one-by-one like this
extra_arg1="${#:$i:1}"
((i++))
extra_arg2="${#:$i:1}"
((i++))
# Print the output
echo "array1:"
print_one_array "${array1[#]}"
echo "array2:"
print_one_array "${array2[#]}"
echo "extra_arg1 = $extra_arg1"
echo "extra_arg2 = $extra_arg2"
echo "extra_args_array:"
print_one_array "${extra_args_array[#]}"
}
Example usage:
echo "Printing array1 and array2 plus some extra args"
print_two_arrays_plus_extra_args "${#array1[#]}" "${array1[#]}" \
"${#array2[#]}" "${array2[#]}" "hello" "world"
Example Output:
Printing array1 and array2 plus some extra args
array1:
one
two
three
array2:
four
five
six
seven
eight
extra_arg1 = hello
extra_arg2 = world
extra_args_array:
hello
world
References:
I referenced a lot of my own sample code from my eRCaGuy_hello_world repo here:
array_practice.sh
array_slicing_demo.sh
[my answer on bash array slicing] Unix & Linux: Bash: slice of positional parameters
An answer to my question on "How can I create and use a backup copy of all input args ("$#") in bash?" - very useful for general array manipulation of the input argument array
An answer to "How to pass array as an argument to a function in Bash", which confirmed to me this really important concept that:
You cannot pass an array, you can only pass its elements (i.e. the expanded array).
See also:
[another answer of mine on this topic] How to pass array as an argument to a function in Bash
Requirement: Function to find a string in an array.
This is a slight simplification of DevSolar's solution in that it uses the arguments passed rather than copying them.
myarray=('foobar' 'foxbat')
function isInArray() {
local item=$1
shift
for one in $#; do
if [ $one = $item ]; then
return 0 # found
fi
done
return 1 # not found
}
var='foobar'
if isInArray $var ${myarray[#]}; then
echo "$var found in array"
else
echo "$var not found in array"
fi
You can also create a json file with an array, and then parse that json file with jq
For example:
my-array.json:
{
"array": ["item1","item2"]
}
script.sh:
ARRAY=$(jq -r '."array"' $1 | tr -d '[],"')
And then call the script like:
script.sh ./path-to-json/my-array.json
You can find more ideas in this similar question: How to pass array as an argument to a function in Bash