#!/bin/bash
FILES=/INPUT/*
OUTPUT=/OUTPUT
for f in $FILES
do
    awk '{ print $3 }' $f > $OUTPUT/$f_1c
done

awk '{ print $3 }' $f > $OUTPUT/${f}_1c
                                ^^^^

file_name=$(basename "$f")
awk '{ print $3 }' $f > $OUTPUT/${file_name}_1c

#!/bin/bash
FILES=/INPUT/*
OUTPUT=/OUTPUT
for f in $FILES
do
    file_name=$(basename "$f")
    awk '{ print $3 }' $f > $OUTPUT/${file_name}_1c
done