Member Avatar for leghorn

we know perl gives us the facility to use hashes

%ages = ('Martin' => 28, 'Sharon' => 35, 'Rikke' => 29);

what if I want to do the same thing in shell script ??

thanks

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  • Latest Post Latest Post by masijade

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Short answer for : shells are not all the same. Modern interactive shells (Bash 4+, ksh93, zsh, etc.) provide true associative arrays; classic POSIX /bin/sh does not. was pointing in the right direction; ’s command-substitution example is a different topic (capturing command output into a variable) rather than a hash data structure.

Bash example (works in Bash 4+):

declare -A ages
ages=( [Martin]=28 [Sharon]=35 [Rikke]=29 )

# read one value
printf '%s\n' "${ages[Martin]}"

# iterate keys
for name in "${!ages[@]}"; do
  printf '%s -> %s\n' "$name" "${ages[$name]}"
done

Always quote expansions (keys or values) and prefer a variable for any key that may contain spaces: k='Full Name'; echo "${ages[$k]}".

Portable alternatives for /bin/sh (no associative arrays): keep the mapping in a small lookup table or call out to awk/perl/python. Example using a here-doc + awk lookup (POSIX-friendly):

ages='
Martin:28
Sharon:35
Rikke:29
'

get_age() {
  printf '%s' "$ages" | awk -F: -v name="$1" '$1==name{print $2; exit}'
}

get_age Sharon   # prints 35

A common hack is name-prefixed variables (age_Martin=28) and a guarded eval to retrieve them; that works but needs careful input validation to avoid injection.

Notes and troubleshooting: check the shell version before using associative arrays ([ -z "$BASH_VERSION" ] || [ "${BASH_VERSINFO[0]}" -lt 4 ] to detect old Bash). Associative arrays are not POSIX, key order is not guaranteed, and eval-based tricks can be unsafe—use an external tool (awk/python) for more complex maps.

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Member Avatar for masijade

At least in the bash and korn shells there are associative arrays, essentially hashes.

See this for bash and this for korn.

Edited by masijade because: added korn shell link
Member Avatar for rubberman

It depends upon what you want to do. In bash scripts you can assign the output of any other executable to a variable using the back-quote character, as in:

varname=`md5sum filename`
Edited by rubberman
Member Avatar for masijade

It depends upon what you want to do.

Sorry rubberman, but did you maybe reply in the wrong thread?

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