Question

I am writing a bash script where i will need to check a directory for existing files and look at the last 4 digits of the first segment of the file name to set the counter when adding new files to the directory.

Naming Scructure:

yymmddHNAZXLCOM0001.835

I need to put the portion in the example 0001 into a CTR variable so the next file it puts into the directory will be

yymmddHNAZXLCOM0002.835

and so on.

what would be the easiest and shortest way to do this?

Answer 1

You can do this with sed:

filename="yymmddHNAZXLCOM0001.835"
first_part=$(echo $filename | sed -e 's/\(.*\)\([0-9]\{4,4\}\)\.\(.*\)/\1/')
counter=$(echo $filename | sed -e 's/\(.*\)\([0-9]\{4,4\}\)\.\(.*\)/\2/')
suffix=$(echo $filename | sed -e 's/\(.*\)\([0-9]\{4,4\}\)\.\(.*\)/\3/')
echo "$first_part$(printf "%04u" $(($counter + 1))).$suffix"
=> "yymmddHNAZXLCOM0002.835"

All three sed calls use the same regular expression. The only thing that changes is the group selected to return. There’s probably a way to do all of that in one call, but my sed-fu is rusty.

Alternate version, using a Bash array:

filename="yymmddHNAZXLCOM0001.835"
ary=($(echo $filename | sed -e 's/\(.*\)\([0-9]\{4,4\}\)\.\(.*\)/\1 \2 \3/'))
echo "${ary[0]}$(printf "%04u" $((${ary[1]} + 1))).${ary[2]}"
=> "yymmddHNAZXLCOM0002.835"

Note: This version assumes that the filename does not have spaces in it.