How to loop through variables with bash [duplicate]

Question

I have a script like below, and I'd like for the script to loop through variables and create a file for each variable. I have researched and can't find a way to do it. Might be that my googling is subpar.

API="link to API"

#city
newyork="latitude-longitude"
boston="latitude-longitude"
miami="latitude-longitude

curl -s "$API$city" > $city.txt

I have tried putting the variables in a different file and then making a loop for each line, but then the script of course included the name of the variable. Unsure of how to attack this issue without using an array.

Why exactly do you want "to attack this issue without using an array" in the first place? What's wrong with cities=([ny]="x1" [boston]="y2" [miami]="z3")? — Andrey Tyukin
– Andrey Tyukin, Commented Nov 14, 2022 at 15:30
I'm not very familiar with arrays, and feel that if I use it there will be more issues later on. — Arawelo
– Arawelo, Commented Nov 14, 2022 at 15:40
Well, familiar or not, it's definitely going to be easier than messing with something like indirect variable references. — Andrey Tyukin
– Andrey Tyukin, Commented Nov 14, 2022 at 15:43
@Arawelo This post has examples of what you are trying to accomplish using various methods: unix.stackexchange.com/questions/459692/loop-through-variables. Consider reading in cities from a file so you don't have to edit the script every time the list changes, — Gary_W
– Gary_W, Commented Nov 14, 2022 at 15:56

Arnaud Valmary · Accepted Answer · 2022-11-14 16:09:46Z

2

Two solutions for input data: hash (solution by Andrey Tyukin) or file

Hash

#! /usr/bin/env bash

API="link to API"

# cities
declare -A CITIES_HASH=(
    ["newyork"]="latitude-longitude"
    ["boston"]="latitude-longitude"
    ["miami"]="latitude-longitude"
)

# "[@]" for all hash entries prefixed by "!" to obtains keys instead of values
for CITY in "${!CITIES_HASH[@]}"; do
    curl -s "$API${CITIES_HASH[$CITY]}" > "${CITY}.txt"
done

File

#! /usr/bin/env bash

API="link to API"

while read -r; do
    [[ -z "${REPLY}" ]] && continue
    CITY="${REPLY%%=*}"
    LAT_LONG="${REPLY#*=}"
    LAT_LONG="${LAT_LONG//\"/}"
    curl -s "$API$LAT_LONG" > "${CITY}.txt"
done <<<"$(cat latitude-longitude.txt; echo)"

Alternative with `!`

echo "Alternative"
#cities
newyork="ny-latitude-longitude"
boston="bo-latitude-longitude"
miami="mi-latitude-longitude"

for CITY in newyork boston miami; do
    echo curl -s "$API${!CITY}" ">" "${CITY}.txt"
done

No solution is better than other. It depends about your source. Of course, if you read files like /usr/share/zoneinfo/zone.tab, the second method may be the right (with adaptations).

edited Nov 14, 2022 at 16:09

answered Nov 14, 2022 at 16:04

Arnaud Valmary

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3 Comments

tjm3772 Over a year ago

why <<<"$(cat latitude-longitude.txt; echo)" vs the much simpler <latitude-longitude.txt?

Arnaud Valmary Over a year ago

Just for forcing a line feed at end of flow

gniourf_gniourf Over a year ago

It's unnecessary to add these echo, since trailing newlines are deleted in a command substitution:

Bash performs the expansion by executing command in a subshell environment and replacing the command substitution with the standard output of the command, with any trailing newlines deleted.

See the corresponding section in the Bash Reference Manual.

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