I'm writing a bash script and I need to check if a file name has a number at the end (after a period) and if so get it, but I can't figure out how to use regex on a variable or string.
I was able to use echo in the terminal to pipe a string into grep, like this:
echo "filename.txt.123" | egrep -o "\.[0-9]+$" | egrep -o "[0-9]+"But I need to assign the output of this to a variable. I tried doing this:
revNumber= echo "filename.txt.123" | egrep -o "\.[0-9]+$" | egrep -o "[0-9]+"But that doesn't work. I tried a bunch of other things as well, but nothing was valid.
In my bash script I want to use grep on a variable and not a string, but the concept here is the same.
How can I use grep on a string or variable and then save the result into another variable?
13 Answers
To assign the output of a command to a variable, use $():
revNumber=$(echo "filename.txt.123" | egrep -o "\.[0-9]+$" | egrep -o "[0-9]+")If all you care about is matching, you might want to consider case:
case foo in f*) echo starts with f ;; *) echo does not start with f ;;
esacWhy the grep and echo I/O overkill, I'd suggest using bash string processing capabilities:
TESTFNAME="filename.txt.283" # you can collect this from doing an ls in the target directory
# acquire last extension using a regexp, including the '.':
FEXT=$(expr "$TESTFNAME" : '.*\(\.[[:digit:]][[:digit:]]*\)')
# check if length is more than just the dot, that means we've got digits:
if [ ${#FEXT} -gt 1 ]; then echo "Gotcha!" $testFilename ${#FEXT} $FEXT # do whatever you like with the file
fiThe regex can be optimized and isn't perfect, but here are the basics:
- .* at the beginning will search at the end of the file.
- [[:digit::]] is almost the same as [0-9], but I find it more readable
Check out other bash string manipulation capabilities at TLDP here.
The below is another option that uses a bash regex comparison before extracting the value at the end of the string.
if [[ $TESTFNAME =~ \.[0-9]+$ ]]; then VAL=$(egrep -o '[0-9]+$' <<<"$TESTFNAME")
fi
