Bash script to extract substring, convert to integer

Question

I am in the process of writing a Bash script which executes a command that returns strings bearing the form

/folder/file_NNNN llll.killAt="nn...nn"

I want to do the following

• extract the numeric part in quotes after .killAt=
• compare it against the current time
• delete the file in question if the current time is greater

My bash skills are limited. I tried identifying the index of the killAt part by issuing an

ndx=`expr index "$rslt" killAt` 

the thinking being that once I am in possession of the index I could extract the numeric bit and work on it. However, what I am getting in ndx is not at all the position of KillAt so clearly I am making a mistake. I am not sure that the presence of /, - and " in the string to be searched is not going to pose a problem.

I can accomplish all of the above by running a PHP script but if I do it will be more because I can't get the Bash script right.

Answer 1

expr is really only needed for doing regular expression matches in POSIX shell. All its the other functionality is implemented in bash itself.

# A regular expression to match against the file name.
# Adjust as necessary; the (.*) is capture group to
# extract the timestamp.
regex='/folder/file_???? ????\.killAt="(.*)"'
# Match, and if it succeeds, retrieve the captured time
# from the BASH_REMATCH array.
if [[ $rslt =~ $regex ]]; then
    ndx=${BASH_REMATCH[1]}
    if (( ndx > $(date +%s) )); then
        rm "$rslt"
    fi
fi