3 added 69 characters in body
source | link

The following code does not preserve the last file of each month.

#! /bin/bash

cmp_timestamp=$(date --date="60 days ago" +%Y%m%d)

while read filename; do
        [[ $filename =~ _(20[0-9][0-9][01][0-9][0123][0-9])\. ]]
        timestamp=${BASH_REMATCH[1]}
        printf "%-40s : %s\n" "$filename" "${timestamp}" 
        if [ "$timestamp" -lt "$cmp_timestamp" ]; then
                echo "   delete this file"
                : rm "$filename"
        else
                echo "   DO NOT delete this file"
        fi
        echo
done <file

From man bash:

BASH_REMATCH
An array variable whose members are assigned by the =~ binary operator to
the [[ conditional command.  The element with index 0 is the portion of the
string  matching  the entire regular expression.  The element with index n
is the portion of the string matching the nth parenthesized subexpression.
This variable is read-only.
#! /bin/bash

cmp_timestamp=$(date --date="60 days ago" +%Y%m%d)

while read filename; do
        [[ $filename =~ _(20[0-9][0-9][01][0-9][0123][0-9])\. ]]
        timestamp=${BASH_REMATCH[1]}
        printf "%-40s : %s\n" "$filename" "${timestamp}" 
        if [ "$timestamp" -lt "$cmp_timestamp" ]; then
                echo "   delete this file"
                : rm "$filename"
        else
                echo "   DO NOT delete this file"
        fi
        echo
done <file

From man bash:

BASH_REMATCH
An array variable whose members are assigned by the =~ binary operator to
the [[ conditional command.  The element with index 0 is the portion of the
string  matching  the entire regular expression.  The element with index n
is the portion of the string matching the nth parenthesized subexpression.
This variable is read-only.

The following code does not preserve the last file of each month.

#! /bin/bash

cmp_timestamp=$(date --date="60 days ago" +%Y%m%d)

while read filename; do
        [[ $filename =~ _(20[0-9][0-9][01][0-9][0123][0-9])\. ]]
        timestamp=${BASH_REMATCH[1]}
        printf "%-40s : %s\n" "$filename" "${timestamp}" 
        if [ "$timestamp" -lt "$cmp_timestamp" ]; then
                echo "   delete this file"
                : rm "$filename"
        else
                echo "   DO NOT delete this file"
        fi
        echo
done <file

From man bash:

BASH_REMATCH
An array variable whose members are assigned by the =~ binary operator to
the [[ conditional command.  The element with index 0 is the portion of the
string  matching  the entire regular expression.  The element with index n
is the portion of the string matching the nth parenthesized subexpression.
This variable is read-only.
2 added 393 characters in body
source | link
#! /bin/bash

cmp_timestamp=$(date --date="60 days ago" +%Y%m%d)

while read filename; do
        [[ $filename =~ _(20[0-9][0-9][01][0-9][0123][0-9])\. ]]
        timestamp=${BASH_REMATCH[1]}
        printf "%-40s : %s\n" "$filename" "${timestamp}" 
        if [ "$timestamp" -lt "$cmp_timestamp" ]; then
                echo "   delete this file"
                : rm "$filename"
        else
                echo "   DO NOT delete this file"
        fi
        echo
done <file

From man bash:

BASH_REMATCH
An array variable whose members are assigned by the =~ binary operator to
the [[ conditional command.  The element with index 0 is the portion of the
string  matching  the entire regular expression.  The element with index n
is the portion of the string matching the nth parenthesized subexpression.
This variable is read-only.
#! /bin/bash

cmp_timestamp=$(date --date="60 days ago" +%Y%m%d)

while read filename; do
        [[ $filename =~ _(20[0-9][0-9][01][0-9][0123][0-9])\. ]]
        timestamp=${BASH_REMATCH[1]}
        printf "%-40s : %s\n" "$filename" "${timestamp}" 
        if [ "$timestamp" -lt "$cmp_timestamp" ]; then
                echo "   delete this file"
                : rm "$filename"
        else
                echo "   DO NOT delete this file"
        fi
        echo
done <file
#! /bin/bash

cmp_timestamp=$(date --date="60 days ago" +%Y%m%d)

while read filename; do
        [[ $filename =~ _(20[0-9][0-9][01][0-9][0123][0-9])\. ]]
        timestamp=${BASH_REMATCH[1]}
        printf "%-40s : %s\n" "$filename" "${timestamp}" 
        if [ "$timestamp" -lt "$cmp_timestamp" ]; then
                echo "   delete this file"
                : rm "$filename"
        else
                echo "   DO NOT delete this file"
        fi
        echo
done <file

From man bash:

BASH_REMATCH
An array variable whose members are assigned by the =~ binary operator to
the [[ conditional command.  The element with index 0 is the portion of the
string  matching  the entire regular expression.  The element with index n
is the portion of the string matching the nth parenthesized subexpression.
This variable is read-only.
1
source | link

#! /bin/bash

cmp_timestamp=$(date --date="60 days ago" +%Y%m%d)

while read filename; do
        [[ $filename =~ _(20[0-9][0-9][01][0-9][0123][0-9])\. ]]
        timestamp=${BASH_REMATCH[1]}
        printf "%-40s : %s\n" "$filename" "${timestamp}" 
        if [ "$timestamp" -lt "$cmp_timestamp" ]; then
                echo "   delete this file"
                : rm "$filename"
        else
                echo "   DO NOT delete this file"
        fi
        echo
done <file