Question

file.txt contains:

##w##

##wew##

using mac 10.6, bash shell, the command:

cat file.txt | grep [[:alpha:]]* -o

outputs nothing. I’m trying to extract the text inside the hash signs. What am i doing wrong?

Answer 1

(Note that it is better practice in this instance to pass the filename as an argument to grep instead of piping the output of cat to grep: grep PATTERN file instead of cat file | grep PATTERN.)

What shell are you using to execute this command? I suspect that your problem is that the shell is interpreting the asterisk as a wildcard and trying to glob files.

Try quoting your pattern, e.g. grep '[[:alpha:]]*' -o file.txt.

I’ve noticed that this works fine with the version of grep that’s on my Linux machine, but the grep on my Mac requires the command grep -E '[[:alpha:]]+' -o file.txt.