I'm having some trouble writing a command that includes a String of a variable in Bash and wanted to know the correct way to do it.
I want to try and fill the Row arrays with the numbers 1-9 but I'm getting myself stuck when trying to pass a variable Row$Line[$i]=$i.
Row0=()
Row1=()
Row2=()
FillArrays() {
for Line in $(seq 0 2)
do
for i in $(seq 1 9)
do
Row$Line[$i]=$i
done
done
}
I can get the desired result if I echo the command but I assume that is just because it is a String.
I want the for loop to select each row and add the numbers 1-9 in each array.
FillArrays() {
for ((Line=0; Line<8; Line++)); do
declare -g -a "Row$Line" # Ensure that RowN exists as an array
declare -n currRow="Row$Line" # make currRow an alias for that array
for ((i=0; i<9; i++)); do # perform our inner loop...
currRow+=( "$i" ) # ...and populate the target array...
done
unset -n currRow # then clear the alias so it can be reassigned later.
done
}
References:
https://wiki.bash-hackers.org/syntax/ccmd/c_for describes the C-style for loop in bash
BashFAQ #6 discusses indirect reference and assignment in detail, including techniques that precede namevars.
Variable expansion happens too late for an assignment to understand it. You can delay the assignment by using the declare builtin. -g is needed in a function to make the variable global.
Also, you probably don't want to use $Line as the array index, but $i, otherwise you wouldn't populate each line array with numbers 1..9.
#! /bin/bash
Row0=()
Row1=()
Row2=()
FillArrays() {
for Line in $(seq 0 8)
do
for i in $(seq 1 9)
do
declare -g Row$Line[$i]=$i
done
done
}
FillArrays
echo "${Row1[#]}"
But note that using variables as parts of variable names is dangerous. For me, needing this always means I need to switch from the shell to a real programming language.
Related
How to return assciative arrays from zsh function?
I tried:
creatAARR() {
declare -A AARR=([k1]=2 [k2]=4)
return $AARR
}
creatAARR
But i get error:
creatAARR:return:2: too many arguments
What is the right way?
EDIT:
I captured output to standard output, like how #chepner suggests, but the new variable doesn't seem to behave like an associative array:
creatAARR() {
declare -A AARR=([k1]=2 [k2]=4)
echo "$AARR"
}
declare -A VALL
NEW_ARR=$(creatAARR)
echo "$NEW_ARR" # 2 4
echo "k1: $NEW_ARR[k1]" # prints just k1:
return
Any suggestions?
return accepts only an integer and sets the exit status of the function.
Shell commands cannot actually return values. If you want pass information to the caller of your function, you have a couple of options available to you:
You could print your return value, but this then relies on you to properly format your output and for the caller to correctly parse it. For associative arrays, there are so many ways that this can go wrong; I wouldn’t recommend doing this.
In Zsh, there is a convention that, to communicate a return value, a function can set $REPLY to a scalar value or $reply to an array. Unfortunately, there is no convention for passing associative arrays. You could, of course, put your key-value pairs simply as elements in the non-associative array $reply and then let the caller cast it to or wrap it in an associative array, but this would break the convention and thus might violate your caller's expectations.
The, in my opinion, best approach is to let the caller specify the name of an associative array, which you can then populate with values. This is also handy when you want to return multiple values of any type, since you can let the caller specify multiple variable names.
This last approach you can use as follows:
% creatAARR() {
# Restrict $name to function scope.
local name=$1
# Delete $1, so $# becomes the other args.
shift
# Assign elements to array.
set -A "$name" "$#"
}
% typeset -A AARR=() # Declare assoc. array
% creatAARR AARR k1 2 k2 4
% typeset -p1 AARR # Print details
typeset -A AARR=(
[k1]=2
[k2]=4
)
I've been able to get my requirement with this:
declare -A VAR1
declare -A VAR2
TYPE_VAR1="TYPE_VAR1"
TYPE_VAR2="TYPE_VAR2"
creatAARR() {
declare -A AARR=([k1]=2 [k2]=4)
case $1 in
"$TYPE_VAR1")
set -A VAR1 ${(kv)AARR}
;;
"$TYPE_VAR2")
set -A VAR2 ${(kv)AARR}
;;
esac
}
creatAARR $TYPE_VAR1 $VAR1
echo "${(kv)VAR1}"
return
There may be a better way, but this is what works for me now.
Please feel free to add in your methods.
I have a variable ($OUTPUT) that contains the following name / value pairs:
member_id=4611686018429783292
platform=Xbox
platform_id=1
character_id=2305843009264966985
period_dt=2020-11-25 20:31:14.923158 UTC
mode=all Crucible modes
mode_id=5
activities_entered=18
activities_won=10
activities_lost=8
assists=103
kills=233
average_kill_distance=15.729613
total_kill_distance=3665
seconds_played=8535
deaths=118
average_lifespan=71.72269
total_lifespan=8463.277
opponents_defeated=336
efficiency=2.8474576
kills_deaths_ratio=1.9745762
kills_deaths_assists=2.411017
suicides=1
precision_kills=76
best_single_game_kills=-1
Each line ends with \n.
I want to loop through them, and parse them into an associative array, and the access the values in the array by the variable names:
while read line
do
key=${line%%=*}
value=${line#*=}
echo $key=$value
data[$key]="$value"
done < <(echo "$OUTPUT")
#this always prints the last value
echo ${data['seconds_played']}
This seems to work, i.e. key/value print the right values, but when I try to pull any values from the array, it always returns the last value (in this case -1).
I feel like im missing something obvious, but have been banging my head against it for a couple of hours.
UPDATE: My particular issue is I'm running a version of bash (3.2.57 on OSX) that doesn't support associative arrays). I'll mark the correct answer below.
Without declare -A data, then data is a normal array. In normal arrays expressions in [here] first undergo expansions, then arithmetic expansion. Inside arithmetic expansion unset variables are expanded to 0. You are effectively only just setting data[0]=something, because data[$key] is data[seconds_played] -> variable seconds_played is not defined, so it expands to data[0]
Add declare -A data and it "should work". You could also just:
declare -A data
while IFS== read -r key value; do
data["$key"]="$value"
done <<<"$OUTPUT"
Try declaring data as an associative array before populating it, eg:
$ typeset -A data # declare as an associative array
$ while read line
do
key=${line%%=*}
value=${line#*=}
echo $key=$value
data[$key]="$value"
done <<< "${OUTPUT}"
$ typeset -p data
declare -A data=([mode]="all Crucible modes" [period_dt]="2020-11-25 20:31:14.923158 UTC" [deaths]="118" [best_single_game_kills]="-1" [efficiency]="2.8474576" [precision_kills]="76" [activities_entered]="18" [seconds_played]="8535" [total_lifespan]="8463.277" [average_lifespan]="71.72269" [character_id]="2305843009264966985" [kills]="233" [activities_won]="10" [average_kill_distance]="15.729613" [activities_lost]="8" [mode_id]="5" [assists]="103" [suicides]="1" [total_kill_distance]="3665" [platform]="Xbox" [kills_deaths_ratio]="1.9745762" [platform_id]="1" [kills_deaths_assists]="2.411017" [opponents_defeated]="336" [member_id]="4611686018429783292" )
$ echo "${data['seconds_played']}"
8535
I am a bit new to the bash scripting. So please bear with me. I am trying to create a table and assign the values in for loop like this:
packages=("foo" "bar" "foobar")
packageMap=()
function test() {
i=0;
for package in "${packages[#]}"
do
echo $i
packageMap[$package]=$i
i=$(expr $i + 1)
done
}
test
echo the first value is ${packageMap["foo"]}
The output for this is:
0
1
2
the first value is 2
While my expected output is:
0
1
2
the first value is 0
So basically the variable's reference is being assigned to this rather than the value. How to solve this?
My bash version:
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin16)
TIA
bash 3.2 only has indexed arrays, so packageMap[$package] only works as intended if $package is an integer, not an arbitrary string.
(What you are observing is $package being evaluated in an arithmetic context, where foo, bar, and foobar are recursively expanded until you get an integer value. Undefined variables expand to 0, so packageMap[foo] is equivalent to packageMap[0].)
If you were using bash 4 or later, you could use an associative array:
packages=("foo" "bar" "foobar")
declare -A packageMap
test () {
i=0
for package in "${packages[#]}"
do
echo $i
packageMap[$package]=$i
i=$(($i + 1))
done
}
Given that i is the same as the index of each element of packages, you could also write
test () {
for i in "${!packages[#]}"; do
package=${packages[i]}
packageMap[$package]=$i
done
}
instead of explicitly incrementing i.
As chep says, there are no associative arrays in bash 3. That said, if you don't mind wasting a bit of CPU, you can use functions to similar effect:
#!/bin/bash
packages=("foo" "bar" "foobar")
function packagemap () {
local i
for i in "${!packages[#]}"; do
[[ ${packages[$i]} = $1 ]] && echo "$i" && return
done
echo "unknown"
}
echo "the first value is $(packagemap "foo")"
The ${!array[#]} construct expands to the set of indices for the array, which for a normally non-associative array consist of incrementing integers starting at 0. But array members can be removed without the indices being renumbered (i.e. unset packages[1]), so it's important to be able to refer to actual indices rather than assuming they're sequential with for loop that simply counts.
And I note that you're using Darwin. Remember that you really need it, you can install bash 4 using Homebrew or MacPorts.
Say I have two associative arrays in Bash
declare -A a
declare -A b
a[xz]=1
b[xz]=2
a[zx]=3
b[zx]=4
I want to do something like this
for arr in ${a[#]} ${b[#]}; do echo ${arr[zx]}; done
and get 3 and 4 in output
but I get
$ for arr in ${a[#]} ${b[#]}; do echo ${arr[zx]}; done
1
3
2
4
Is there a way to do this in Bash?
You don't want to iterate over the contents; you want to iterate over the names of the arrays, then use indirect expansion to get the desired value of the fixed key from each array.
for arr in a b; do
t=$arr[zx] # first a[zx], then b[zx]
printf '%s\n' "${!t}"
done
Here, the variable "name" for use in indirect expansion is the name of the array along with the desired index.
Assuming the keys in both the arrays match(a major assumption), you can use one array as reference and loop over the keys and print in each array.
for key in "${!a[#]}"; do
printf "Array-1(%s) %s Array-2(%s) %s\n" "$key" "${a[$key]}" "$key" "${b[$key]}"
done
which produces an output as below. You can of-course remove the fancy debug words(Array-1, Array-2) which was added just for an understanding purpose.
Array-1(xz) 1 Array-2(xz) 2
Array-1(zx) 3 Array-2(zx) 4
One general good practice is always quote (for key in "${!a[#]}") your array expansions in bash, so that the elements are not subjected to word-splitting by the shell.
After thoroughly searching for a way to create an associative array in bash, I found that declare -A array will do the trick. But the problem is, it is only for bash version 4 and the bash version the server has in our system is 3.2.16.
How can I achieve some sort of associative array-like hack in bash 3? The values will be passed to a script like
ARG=array[key];
./script.sh ${ARG}
EDIT: I know that I can do this in awk, or other tools but strict bash is needed for the scenario I am trying to solve.
Bash 3 has no associative arrays, so you're going to have to use some other language feature(s) for your purpose. Note that even under bash 4, the code you wrote doesn't do what you claim it does: ./script.sh ${ARG} does not pass the associative array to the child script, because ${ARG} expands to nothing when ARG is an associative array. You cannot pass an associative array to a child process, you need to encode it anyway.
You need to define some argument passing protocol between the parent script and the child script. A common one is to pass arguments in the form key=value. This assumes that the character = does not appear in keys.
You also need to figure out how to represent the associative array in the parent script and in the child script. They need not use the same representation.
A common method to represent an associative array is to use separate variables for each element, with a common naming prefix. This requires that the key name only consists of ASCII letters (of either case), digits and underscores. For example, instead of ${myarray[key]}, write ${myarray__key}. If the key is determined at run time, you need a round of expansion first: instead of ${myarray[$key]}, write
n=myarray__${key}; echo ${!n}
For an assignment, use printf -v. Note the %s format to printf to use the specified value. Do not write printf -v "myarray__${key}" %s "$value" since that would treat $value as a format and perform printf % expansion on it.
printf -v "myarray__${key}" %s "$value"
If you need to pass an associative array represented like this to a child process with the key=value argument representation, you can use ${!myarray__*} to enumerate over all the variables whose name begins with myarray__.
args=()
for k in ${!myarray__*}; do
n=$k
args+=("$k=${!n}")
done
In the child process, to convert arguments of the form key=value to separate variables with a prefix:
for x; do
if [[ $x != *=* ]]; then echo 1>&2 "KEY=VALUE expected, but got $x"; exit 120; fi
printf -v "myarray__${x%%=*}" %s "${x#*=}"
done
By the way, are you sure that this is what you need? Instead of calling a bash script from another bash script, you might want to run the child script in a subshell instead. That way it would inherit from all the variables of the parent.
Here is another post/explanation on associative arrays in bash 3 and older using parameter expansion:
https://stackoverflow.com/a/4444841
Gilles' method has a nice if statement to catch delimiter issues, sanitize oddball input ...etc. Use that.
If you are somewhat familiar with parameter expansion:
http://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html
To use in your scenario [ as stated: sending to script ]:
Script 1:
sending_array.sh
# A pretend Python dictionary with bash 3
ARRAY=( "cow:moo"
"dinosaur:roar"
"bird:chirp"
"bash:rock" )
bash ./receive_arr.sh "${ARRAY[#]}"
Script 2: receive_arr.sh
argAry1=("$#")
function process_arr () {
declare -a hash=("${!1}")
for animal in "${hash[#]}"; do
echo "Key: ${animal%%:*}"
echo "Value: ${animal#*:}"
done
}
process_arr argAry1[#]
exit 0
Method 2, sourcing the second script:
Script 1:
sending_array.sh
source ./receive_arr.sh
# A pretend Python dictionary with bash 3
ARRAY=( "cow:moo"
"dinosaur:roar"
"bird:chirp"
"bash:rock" )
process_arr ARRAY[#]
Script 2: receive_arr.sh
function process_arr () {
declare -a hash=("${!1}")
for animal in "${hash[#]}"; do
echo "Key: ${animal%%:*}"
echo "Value: ${animal#*:}"
done
}
References:
Passing arrays as parameters in bash
If you don't want to handle a lot of variables, or keys are simply invalid variable identifiers, and your array is guaranteed to have less than 256 items, you can abuse function return values. This solution does not require any subshell as the value is readily available as a variable, nor any iteration so that performance screams. Also it's very readable, almost like the Bash 4 version.
Here's the most basic version:
hash_index() {
case $1 in
'foo') return 0;;
'bar') return 1;;
'baz') return 2;;
esac
}
hash_vals=("foo_val"
"bar_val"
"baz_val");
hash_index "foo"
echo ${hash_vals[$?]}
More details and variants in this answer
You can write the key-value pairs to a file and then grep by key. If you use a pattern like
key=value
then you can egrep for ^key= which makes this pretty safe.
To "overwrite" a value, just append the new value at the end of the file and use tail -1 to get just the last result of egrep
Alternatively, you can put this information into a normal array using key=value as value for the array and then iterator over the array to find the value.
This turns out to be ridiculously easy. I had to convert a bash 4 script that used a bunch of associative arrays to bash 3. These two helper functions did it all:
array_exp() {
exp=${#//[/__}
eval "${exp//]}"
}
array_clear() {
unset $(array_exp "echo \${!$1__*}")
}
I'm flabbergasted that this actually works, but that's the beauty of bash.
E.g.
((all[ping_lo] += counts[ping_lo]))
becomes
array_exp '((all[ping_lo] += counts[ping_lo]))'
Or this print statement:
printf "%3d" ${counts[ping_lo]} >> $return
becomes
array_exp 'printf "%3d" ${counts[ping_lo]}' >> $return
The only syntax that changes is clearing. This:
counts=()
becomes
array_clear counts
and you're set. You could easily tell array_exp to recognize expressions like "=()" and handle them by rewriting them as array_clear expressions, but I prefer the simplicity of the above two functions.