Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
How to find where a command is stored in Linux
Answer:
To find out where a command is stored in Linux, you can use the which command to locate the command
# which wget
/usr/bin/wget
or use whereis command to locate the binary/source/manual
# whereis wget
wget: /usr/bin/wget /usr/share/man/man1/wget.1.gz
How to change the owner of a file in Linux
Answer:
You need to use the chown command:
1. To change the owner of text.txt to john
# chown john /tmp/text.txt
2. To change the owner of text.txt to john, but group identifier to admin.
# chown john:admin /tmp/text.txt
3. To change the group of text.txt to admin
# chown :admin /tmp/text.txt
Reference: http://en.wikipedia.org/wiki/Chown
How to count the number of line in a file
Answer:
Use the wc command
wc -l text.txt
Becareful when using the mtime option in find command
Answer:
A simple command like the following is very handy when finding all the files in the current directory which have been modified within 1 day.
# find -type f -mtime -1
But the above interpretation is simply wrong!
The real meaning of the above command is: Find all the files in the current directory which have been modified less than 2 days.
So if a file is modified before 1.9999999.. day, it still match the above command since the fractional part is ignored.
Try it yourself if you don't believe.
Reference:
man find
Remove empty lines in a file
Answer
Pick any one of the following methods.
1. grep
grep . test.txt
2. sed
sed '/^$/d' test.txt
3. awk
awk NF test.txt
4. tr
cat test.txt | tr -s "\n"
5. perl
perl -n -e 'print unless /^$/' test.txt
