Linux

Hello. In some script, I saw:

Code:

filename=${1:-/etc/hosts}
if [ -r “$filename” ] && [ -s “$filename” ]; then
md5sum $filename
else
echo “$filename can not be processed”
fi
# Show the file if possible
ls -ld $filename 2>/dev/null

What does the first line means? In $filename I still got /etc/hosts.

If no arguments are passed to this script or if the 1st argument passed to this script is an empty string, the shell variable filename will be set to "/etc/hosts"; otherwise the 1st argument passed to the script will be assigned to filename.

So, if your script is named some and you invoke it as:

Code:

./some
    or as
./some ""

then filename will be set to /etc/hosts, but if you invoke it as:

Code:

./some /etc/motd

then filename will be set to /etc/motd.

I understand it completely. Thank you!