Test if File was Modified After Date in File Name

The following script will check the dates of all files specified on the command line:

$ cat check-dates.sh 
#! /bin/bash

for f in "$@" ; do
  # get date portion of filename
  fdate=$(basename "$f" .txt | sed -re 's/^.*(2015)/\1/')

  # convert it to seconds since epoch + 1 day
  fsecs=$(echo $(date +%s -d "$fdate") + 86400 | bc )

  # get modified timestamp of file in secs since epoch
  ftimestamp=$(stat -c %Y "$f")

  [ "$ftimestamp" -gt "$fsecs" ] && echo "$f has been modified after $fdate"
done

$ ./check-dates.sh file-name-20151002.txt 
file-name-20151002.txt has been modified after 20151002
$ ls -l file-name-20151002.txt 
-rw-rw-r-- 1 cas cas 0 Oct 26 19:21 file-name-20151002.txt

Here's another way with GNU date/bash (use it as newer filename):

newer () {
tstamp=${1:${#1}-12:8}
mtime=$(date '+%Y%m%d' -r "$1")
[[ ${mtime} -le ${tstamp} ]] && printf '%s\n' "$1 : NO : mtime is ${mtime}" || printf '%s\n' "$1 : YES : mtime is ${mtime}"
}

output:

file-name-20150909.txt : YES : mtime is 20151026

or

file-name-20151126.txt : NO : mtime is 20151026

You could do this:

• extract the year/month/day values into a shell variable,
• create a temporary file
• use the touch command (adding 0s for hour/minute/second) to set the modification date for the temporary file

Because your question is about bash, you likely are using Linux. The test program used in Linux (part of coreutils) has extensions for timestamp comparison (-nt and -ot) not found in POSIX test.

POSIX comments about this in the rationale for test:

Some additional primaries newly invented or from the KornShell appeared in an early proposal as part of the conditional command ([[]]): s1 > s2, s1 < s2, str = pattern, str != pattern, f1 -nt f2, f1 -ot f2, and f1 -ef f2. They were not carried forward into the test utility when the conditional command was removed from the shell because they have not been included in the test utility built into historical implementations of the sh utility.

Using that extension, you could then

• create another temporary file with the date you want to compare against
• use the -nt operator in test to make the comparison you asked for.

Using bash and stat to get the dates as strings and comparing them:

#!/bin/bash
for file
do  moddate=$(stat -c %y "$file")
    moddate=${moddate%% *} # 2015-10-26
    moddate=${moddate//-/} # 20151026
    if [[ "$file" =~ ([0-9]{8}).txt$ ]]
    then  if [[ $moddate > ${BASH_REMATCH[1]} ]]
          then echo "$file: modified $moddate"
          fi
    fi
done

The bash =~ regexp operator captures the 8 digits of the filename into bash array BASH_REMATCH. [[ ]] compares the strings, though you simply compare them as numbers instead in [ -gt ].

Directly capturing the YYYYMMDD format (8 digits) in the name with a regex:

[[ $a =~ ([0-9]{8}) ]]

And using stat for modification date (in seconds after epoch):

#!/bin/bash

if [[ $1 =~ ([0-9]{8}) ]]; then

    namedate="$(date -ud "${BASH_REMATCH[1]}" "+%s")"
            correct=$?
            if [[ $correct != 0 ]]; then
                echo "Date in the file name $1 seems incorrect"
                exit 2
            fi

    modifdate="$(stat -c '+%Y' $1)"
            correct=$?
            if [[ $correct != 0 ]]; then
                echo "File time for file $1 could not be found"
                exit 3
            fi

    if (( $modifdate > $namedate )); then
                echo "File was modified after the date in its name."
    else
                echo "File has not been modified"
    fi
fi

Please be aware of:

1. Call the script with the file name: ./script.sh file-name-20151002.txt
2. The dates are understood as UTC by the stat from the OS.
3. I do not know in what format are the dates in the file name.
4. I assumed they were also in UTC, that's why the -u option in date.
5. The tests do not take into account "Daylight saving time" effects.
6. Or, local date/time changes.
7. The script does just a basic check for date in the name (and warns).