Is it possible to loop through an array of strings in Bash? The answer is yes.
You can use it like this:
## declare an array variable
declare -a arr=("element1" "element2" "element3")
## now loop through the above array
for i in "${arr[@]}"
do
echo "$i"
# or do whatever with individual element of the array
done
# You can access them using echo "${arr[0]}", "${arr[1]}" also
Also works for multi-line array declaration
declare -a arr=("element1"
"element2" "element3"
"element4"
)That is possible, of course.
for databaseName in a b c d e f; do
# do something like: echo $databaseName
doneHow to loop through an array of strings in Bash?
We can loop through an array of strings in Bash like the following methods:
for Item in Item1 Item2 Item3 Item4 ;
do
echo $Item
done
Output:
Item1
Item2
Item3
Item4
To preserve spaces; single or double quote list entries and double quote list expansions.
for Item in 'Item 1' 'Item 2' 'Item 3' 'Item 4' ;
do
echo "$Item"
done
Output:
Item 1
Item 2
Item 3
Item 4
To make list over multiple lines
for Item in Item1 \
Item2 \
Item3 \
Item4
do
echo $Item
done
Output:
Item1
Item2
Item3
Item4
Simple list variable
List=( Item1 Item2 Item3 )
or
List=(
Item1
Item2
Item3
)
Display the list variable:
echo ${List[*]}
Output:
Item1 Item2 Item3
Loop through the list:
for Item in ${List[*]}
do
echo $Item
done
Output:
Item1
Item2
Item3
Create a function to go through a list:
Loop(){
for item in ${*} ;
do
echo ${item}
done
}
Loop ${List[*]}
Using the declare keyword (command) to create the list, which is technically called an array:
declare -a List=(
"element 1"
"element 2"
"element 3"
)
for entry in "${List[@]}"
do
echo "$entry"
done
Output:
element 1
element 2
element 3
Creating an associative array. A dictionary:
declare -A continent
continent[Vietnam]=Asia
continent[France]=Europe
continent[Argentina]=America
for item in "${!continent[@]}";
do
printf "$item is in ${continent[$item]} \n"
done
Output:
Argentina is in America
Vietnam is in Asia
France is in Europe
CSV variables or files in to a list.
Changing the internal field separator from a space, to whatever you want.
In the example below it is changed to a comma
List="Item 1,Item 2,Item 3"
Backup_of_internal_field_separator=$IFS
IFS=,
for item in $List;
do
echo $item
done
IFS=$Backup_of_internal_field_separator
Output:
Item 1
Item 2
Item 3
If need to number them:
`
this is called a back tick. Put the command inside back ticks.
`command`
It is next to the number one on your keyboard and or above the tab key, on a standard American English language keyboard.
List=()
Start_count=0
Step_count=0.1
Stop_count=1
for Item in `seq $Start_count $Step_count $Stop_count`
do
List+=(Item_$Item)
done
for Item in ${List[*]}
do
echo $Item
done
Output is:
Item_0.0
Item_0.1
Item_0.2
Item_0.3
Item_0.4
Item_0.5
Item_0.6
Item_0.7
Item_0.8
Item_0.9
Item_1.0
Becoming more familiar with bashes behavior:
Create a list in a file
cat <<EOF> List_entries.txt
Item1
Item 2
'Item 3'
"Item 4"
Item 7 : *
"Item 6 : * "
"Item 6 : *"
Item 8 : $PWD
'Item 8 : $PWD'
"Item 9 : $PWD"
EOF
Read the list file in to a list and display
List=$(cat List_entries.txt)
echo $List
echo '$List'
echo "$List"
echo ${List[*]}
echo '${List[*]}'
echo "${List[*]}"
echo ${List[@]}
echo '${List[@]}'
echo "${List[@]}"Answer #3:
In the same spirit as the first answer:
listOfNames="RA
RB
R C
RD"
# To allow for other whitespace in the string:
# 1. add double quotes around the list variable, or
# 2. see the IFS note (under 'Side Notes')
for databaseName in "$listOfNames" # <-- Note: Added "" quotes.
do
echo "$databaseName" # (i.e. do action / processing of $databaseName here...)
done
# Outputs
# RA
# RB
# R C
# RD
B. No whitespace in the names:
listOfNames="RA
RB
R C
RD"
for databaseName in $listOfNames # Note: No quotes
do
echo "$databaseName" # (i.e. do action / processing of $databaseName here...)
done
# Outputs
# RA
# RB
# R
# C
# RD
Notes
- In the second example, using
listOfNames="RA RB R C RD"has the same output.
Other ways to bring in data include:
- stdin (listed below),
- variables,
- an array ,
- a file…
Read from stdin
# line delimited (each databaseName is stored on a line)
while read databaseName
do
echo "$databaseName" # i.e. do action / processing of $databaseName here...
done # <<< or_another_input_method_here
- the bash IFS “field separator to line” [1] delimiter can be specified in the script to allow other whitespace (i.e.
IFS='\n', or for MacOSIFS='\r') - I like the accepted answer also 🙂 — I’ve include these snippets as other helpful ways that also answer the question.
- Including
#!/bin/bashat the top of the script file indicates the execution environment. - It took me months to figure out how to code this simply 🙂
Answer #4:
Surprised that nobody’s posted this yet — if you need the indices of the elements while you’re looping through the array, you can do this:
arr=(foo bar baz)
for i in ${!arr[@]}
do
echo $i "${arr[i]}"
done
Output:
0 foo
1 bar
2 baz
I find this a lot more elegant than the “traditional” for-loop style (for (( i=0; i<${#arr[@]}; i++ ))).
(${!arr[@]} and $i don’t need to be quoted because they’re just numbers; some would suggest quoting them anyway, but that’s just personal preference.)
Answer #5:
Simple way :
arr=("sharlock" "bomkesh" "feluda" ) ##declare array
len=${#arr[*]} # it returns the array length
#iterate with while loop
i=0
while [ $i -lt $len ]
do
echo ${arr[$i]}
i=$((i+1))
done
#iterate with for loop
for i in $arr
do
echo $i
done
#iterate with splice
echo ${arr[@]:0:3}Answer #6:
I used this approach for my GitHub updates, and I found it simple.
## declare an array variable
arr_variable=("kofi" "kwame" "Ama")
## now loop through the above array
for i in "${arr_variable[@]}"
do
echo "$i"
done
You can iterate through bash array values using a counter with three-expression (C style) to read all values and indexes for loops syntax:
declare -a kofi=("kofi" "kwame" "Ama")
# get the length of the array
length=${#kofi[@]}
for (( j=0; j<${length}; j++ ));
do
print (f "Current index %d with value %s\n" $j "${kofi[$j]}")
doneHow to loop through an array of strings in Bash? Answer #7:
Implicit array for script or functions:
In addition to the correct answers above: If the basic syntax for loop is:
for var in "${arr[@]}" ;do ...$var... ;done
there is a special case in bash:
When running a script or a function, arguments passed at command lines will be assigned to $@ array variable, you can access by $1, $2, $3, and so on.
This can be populated (for a test) by
set -- arg1 arg2 arg3 ...
A loop over this array could be written simply:
for item ;do
echo "This is item: $item."
done
Note that the reserved work in is not present and no array name too!
Sample:
set -- arg1 arg2 arg3 ...
for item ;do
echo "This is item: $item."
done
This is item: arg1.
This is item: arg2.
This is item: arg3.
This is item: ....
Note that this is same than
for item in "$@";do
echo "This is item: $item."
done
Then into a script:
#!/bin/bash
for item ;do
printf "Doing something with '%s'.\n" "$item"
done
Save this in a script myscript.sh, chmod +x myscript.sh, then
./myscript.sh arg1 arg2 arg3 ...
Doing something with 'arg1'.
Doing something with 'arg2'.
Doing something with 'arg3'.
Doing something with '...'.
Same in a function:
myfunc() { for item;do cat <<<"Working about '$item'."; done ; }
Then
myfunc item1 tiem2 time3
Working about 'item1'.
Working about 'tiem2'.
Working about 'time3'.Hope you learned something from this post.
Follow Programming Articles for more!