Get the index of a value in a Bash array

Question

I have something in bash like

myArray=(\'red\' \'orange\' \'green\')

And I would like to do something like

echo ${         


        

Answer 1

Another tricky one-liner:

index=$((-1 + 10#0$(IFS=$'\n' echo "${my_array[*]}" | grep --line-number --fixed-strings -- "$value" | cut -f1 -d:)))

features:

• supports elements with spaces
• returns -1 when not found

caveats:

• requires value to be non-empty
• difficult to read

---

Explanations by breaking it down in execution order:

IFS=$'\n' echo "${my_array[*]}"

set array expansion separator (IFS) to a new line char & expand the array

grep --line-number --fixed-strings -- "$value"

grep for a match:

• show line numbers (--line-number or -n)
• use a fixed string (--fixed-strings or -F; disables regex)

• allow for elements starting with a - (--)

  cut -f1 -d:

extract only the line number (format is :)

$((-1 + 10#0$(...)))

subtract 1 since line numbers are 1-indexed and arrays are 0-indexed

• if $(...) does not match:

  • nothing is returned & the default of 0 is used (10#0)
• if $(...) matches:
  • a line number exists & is prefixed with 10#0; i.e. 10#02, 10#09, 10#014, etc
  • the 10# prefix forces base-10/decimal numbers instead of octal

---

---

Using awk instead of grep, cut & bash arithmetic:

IFS=$'\n'; awk "\$0 == \"${value//\"/\\\"}\" {print NR-1}" <<< "${my_array[*]}"

features:

• supports elements with spaces
• supports empty elements
• less commands opened in a subshell

caveats:

• returns when not found

---

Explanations by breaking it down in execution order:

IFS=$'\n' [...] <<< "${my_array[*]}"

set array expansion separator (IFS) to a new line char & expand the array

awk "\$0 == \"${value//\"/\\\"}\" {print NR-1}"

match the entire line & print the 0-indexed line number

• ${value//\"/\\\"} replaces double quotes in $value with escaped versions
• since we need variable substitution, this segment has more escaping than wanted