#!/bin/bash
s="a82411:x:1015:1006:Adriana Morais,,,:/home/a82411:/bin/bash
a60395:x:1016:1006:Afonso Pichel,,,:/home/a60395:/bin/bash
a82420:x:1017:1006:Afonso Alves,,,:/home/a82420:/bin/bash
a69225:x:1018:1006:Afonso Alves,,,:/home/a69225:/bin/bash
a82824:x:1019:1006:Afonso Carreira,,,:/home/a82824:/bin/bash
a83112:x:1020:1006:Aladje Sanha,,,:/home/a83112:/bin/bash
a82652:x:1022:1006:Alexandre Ferreira,,,:/home/a82652:/bin/bash
a83063:x:1023:1006:Alexandre Feijo,,,:/home/a83063:/bin/bash
a82540:x:1024:1006:Ana Santana,,,:/home/a82540:/bin/bash"
awk 'BEGIN {FS=OFS=":"} {sub(/^a/, "", $1); gsub(/,/, "", $5); print $1, $5, _, _ "a" $1 "@"}' <<< "$s"
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