1: Editing without an editor
Very long files are often hard to manipulate with a text editor. If you need to do it regularly, chances are you'll find it much faster to use some handy command-line tools instead, like in the following examples.To print columns eg 1 and 3 from a file file1 into file2, we can use awk:
awk '{print $1, $3}' file1 > file2
To output only characters from column 8 to column 15 of file1, we can use cut:
cut -c 8-15 file1 > file2
To replace the word word1 with the word word2 in the file file1, we can use the sed command:
sed "s/word1/word2/g" file1 > file2
This is often a quicker way to get results than even opening a text editor.
2: Backup selected files only
Want to use tar to backup only certain files in a directory? Then you'll want to use the -T flag as follows. First, create a file with the file you want to backup:
cat >> /etc/backup.conf
# /etc/passwd
# /etc/shadow
# /etc/yp.conf
# /etc/sysctl.conf
EOF
Then run tar with the -T flag pointing to the file just created:
tar -cjf bck-etc-`date +%Y-%m-%d`.tar.bz2 -T /etc/backup.conf
Now you have your backup.
3: Merging columns in files
While splitting columns in files is easy enough, merging them can be complicated. Below is a simple shell script that does the job:
#!/bin/sh
length=`wc -l $1 | awk '{print $1}'`
count=1
[ -f $3 ] && echo "Optionally removing $3" && rm -i $3
while [ "$count" -le "$length" ] ; do
a=`head -$count $1 | tail -1`
b=`head -$count $2 | tail -1`
echo "$a $b" >> $3
count=`expr $count + 1`
done
Give to this script the name merge.sh and make it executable with:
chmod u+x merge.sh
Now, if you want to merge the columns of file1 and file2 into file3, it's just matter of executing
/path/to/merge.sh file1 file2 file3
where /path/to has to be replaced with the location of merge.sh in your filesystem.
4: Case sensitivity
Despite the case of a word not making any difference to other operating systems, in Linux "Command" and "command" are different things. This can cause trouble when moving files from Windows to Linux. tr is a little shell utility that can be used to change the case of a bunch of files.
#!/bin/sh
for i in `ls -1`; do
file1=`echo $i | tr [A-Z] [a-z] `
mv $i $file1 2>/dev/null
done
By executing it, FILE1 and fiLe2 will be renamed respectively file1 and file2.
5: Macros in Emacs
When editing files, you will often find that the tasks are tedious and repetitive, so to spare your time you should record a macro. In Emacs, you will have to go through the following steps:
- Press Ctrl+X to start recording.
- Insert all the keystrokes and commands that you want
- Press Ctrl+X to stop when you're done.
Now, you can execute that with
Ctrl -u <number> Ctrl -x e
where <number> is the number of times you want to execute the macro. If you enter a value of 0, the macro will be executed until the end of the file is reached. Ctrl -x e is equivalent to Ctrl -u 1 Ctrl-x e.
6: Simple spam killing
Spam, or unsolicited bulk email, is such a widespread problem that almost everyone has some sort of spam protection now, out of necessity. Most ISPs include spam filtering, but it isn't set to be too aggressive, and most often simply labels the spam, but lets it through (ISPs don't want to be blamed for losing your mails).The result is that, while you may have anti-spam stuff set up on the client-side, you can make its job easier by writing a few filters to remove the spam that's already labelled as such. The label is included as a header. In KMail, you can just create a quick filter to bin your mail, or direct it to a junk folder. The exact header used will depend on the software your ISP is using, but it's usually something like X-Spam-Flag = YES for systems like SpamAssassin.
Simply create a filter in KMail, choose Match Any of the Following and type in the header details and the action you require. Apply the filter to incoming mail, and you need never be troubled by about half the volume of your spam ever again.
7: Read OOo docs without OOo
Have you ever been left with an OOo document, but no OpenOffice.org in which to read it? Thought you saved it out as plain text (.txt), but used the StarOffice .sxw format instead? The text can be rescued. Firstly, the sxw file is a zip archive, so unzip it:
unzip myfile.sxw
The file you want is called 'content.xml'. Unfortunately, it's so full of xml tags it's fairly illegible, so filter them out with some Perl magic:
cat content.xml | perl -p -e "s/<[^>]*>/ /g;s/\n/ /g;s/ +/ /;"
It may have lost lots of formatting, but at least it is now readable.
8: Find and execute
The find command is not only useful for finding files, but is also useful for processing the ones it finds too. Here is a quick example.Suppose we have a lot of tarballs, and we want to find them all:
find . -name '*.gz'
will locate all the gzip archives in the current path. But suppose we want to check they are valid archives? The gunzip -vt option will do this for us, but we can cunningly combine both operations, using xargs:
find . -name '*.gz' | xargs gunzip -vt
9: Use the correct whois server
The whois command is very useful for tracking down Internet miscreants and the ISPs that are supplying them with service. Unfortunately, there are many whois servers, and if you are querying against a domain name, you often have to use one which is specific to the TLD they are using. However, there are some whois proxies that will automatically forward your query on to the correct server. One of these is available at http://whois.geektools.com. whois -h whois.geektools.com plop.info
10: Where did that drive mount?
A common problem with people who have lots of mountable devices (USB drives, flash memory cards, USB key drives) is working out where that drive you just plugged in has ended up? Practically all devices that invoke a driver - such as usb-storage - will dump some useful information in the logs. Try
dmesg | grep SCSI
This will filter out recognised drive specs from the dmesg output. You'll probably turn up some text like:
SCSI device sda: 125952 512-byte hdwr sectors (64 MB)
DISLAIMER: For education purpose only
Adithya
