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Passing a Bash Array Element to an Awk Regex Expression
awk '$2 ~ /^/var$/ { print $1 }' /etc/fstab

PARTITIONS=(/usr /home /var tmp);
for ((n=0; n<${#PARTITION[@]}; n++)); do
    cat /etc/fstab | awk '$2 ~ /^${PARTITIONS[$n]}$/ { print $1 }';
done

PARTITIONS=(/usr /home /var tmp);
for ((n=0; n<${#PARTITION[@]}; n++)); do
    cat /etc/fstab | awk -v partition="${PARTITIONS[$n]}" '$2 ~ /^/var$/ { print $1," ",partition }';
done

cat /etc/fstab | awk -v partition="${PARTITIONS[$n]}" '$2 ~ partition { print $1 }'

awk -v partition="${partitions[$n]}" '$2 ~ "^/" partition "$" { print $1 }' /etc/fstab

partitions=( /usr /home /var /tmp )
awk '
    FNR==NR { partitions[$0]=""; next }
    $1 !~ /^#/ && ($2 in partitions) { print $1 }
' <(printf '%sn' "${partitions[@]}") /etc/fstab

declare -A 'partitions=([/usr]= [/home]= [/var]= [/tmp]=)'
while read -r spec file vfstype mntops freq passno; do
    [[ $spec != #* && ${partitions[$file]+set} ]] && echo "$spec"
done < /etc/fstab

dirs=( /usr /home /var /tmp )
for dir in "${dirs[@]}"; do
    { read -r; read -r part _; } < <(df -P "$dir")
    echo "$part"
done

awk '$2 ~ "'${PARTITIONS[$n]}'" { print $1 }' /etc/fstab

awk "$2 ~ /${PARTITIONS[$n]////\/}/ { print $1 }" /etc/fstab

PARTITIONS=(/usr /home /var /tmp)
awk -v partition="${PARTITIONS[*]}"
  '$2 != "" && partition ~ $2"\>" { print $1 }' /etc/fstab

$ cat file | program # would normally just be ...
$ program < file

(echo StartFlag ${PARTITIONS[*]}; cat /etc/fstab) | awk ...

awk -v partitions="${PARTITIONS[*]}" '
    BEGIN { split(partitions,a," ") }
    { for (e in a) { if ($2 ~ a[e]) { print $1 } } }' /etc/fstab