Linux Util 2

1) You can try to place a tab between the quotes if you first press "<CTR> v" then the "<TAB>" key:

cut -f1 -d'<ctrl>v <tab>' filename

This way even <tab> character can also made as delimiter in shell scripting.

2) If you have a file where first column is list of years with author names against each year, to find the count of papers in each year:

cut -f1 -d' ' fname |uniq -c

3) To find all empty lines in the standard input:
grep ^$  or  grep -v .   

4) Hmm, long live blogging: I was looking for grep command to search for a text recursively from a given directory and this blogger helped:

http://www.geekality.net/2011/04/12/unix-recursive-search-for-text-in-files/

grep -rl "your_text"

5 ) To redirect the output of time (real, sys, usr) command onto redirect_file, instead of console.

(time your_command your_args) 2>> redirect_file

6) To search for a file's contents in another file:

grep -f searchfile tobesearchedfile -n --color=auto

Can remove the color flag. Got this color tip from Nixcraft

7) To list only the duplicate lines of a file:

uniq -d filename

8) To unzip a file that is only compressed with bz2 use

bunzip2 filename.bz2

9) To unzip things thar are compressed with .tar.bz2 use

tar -xvjpf filename.tar.bz2

I got the tips 8 and 9 from linuxquestions.org

10) Many a times, to know if the server I am working in is serving a lot of users, I type w in the shell prompt. This is useful if you are going to run a resource-greedy process. Now, if you are interested to write/talk to them, you may want to know their full name. The following command helps to get their full names from an administrative database:

getent passwd "jey"|cut -d':' -f5

If you are curious, an encouraging fact is man page of getent is small :) !!
Happy linuxing!!

11) Wow, after about 5 months (it's Jan 8, 2013 today), I am glad to be updating my blog. Yup, it also means I have failed to keep track of my new findings in web in this database. Anyways, the following tip was something very important to me because I realized I am spending too much time 'Alt+tab'ing to find the window I want to work in while working from home, logging to my office machine (essentially all are xterms).

To change the title of the xterm window to indicate something useful (in this example, your_string):
unset PROMPT_COMMAND
echo -ne "\033]0;your_string\007"

I had to call unset first because by default in my .bashrc file, PROMPT_COMMAND stores the username, machine and current working directory. It is important to observe the combination of characters around "your_string" and follow them strictly.

Linux Util 1

1) To paste one of the columns of a multi-column file as one other column in the same file:
cut -f3 -d' ' fname1|paste -d' ' - fname1 > fname2

This command takes the 3rd column of file fname1 and pastes it as first column and writes the content to file fname2. Rename the file fname2 to fname1 to avoid keeping duplicate copies. The hyphen in the paste command can be switched to last to make the 3rd column as the last column instead of first. Here the column separator is the space character given after the '-d' switch.


2) I forget to leave space around binary operator used in expr command in shell scripting.

3) I  keep forgetting about the rules of double quotes and single quotes usage in shell scripting. If you give a single quoted word inside double quoted sentence, the single quote is not interpreted, but a $variable is substituted with its value.

4) To find all C/C++ program files and related header files:

find . -regex '.*\.\(c\|h\|cxx\|cpp\)' -print

This command fetches files with extension .c, .h, .cxx, .cpp and prints their path from the current directory. Please note the extra characters ".*." in the front. The second dot is escaped and so is the first open parenthesis and logical OR symbol '|'.

5) A modification to the above command is by replacing the last 'print' option to 'print0'. That is append number zero to print word. This will display all the file names in one line as against the previous output that prints one file name in one line.

6) If you want the contents of all these files in one go, give the following:

find . -regex '.*\.\(c\|h\|cxx\|cpp\)' -print0|xargs -o cat

7) To remove all spaces in the filenames of a directory, get inside the directory and type in command line:

rename 's/ //g' *

Here, the single space after first '/' is important. Replace '*' with other names if you do not want to apply this change to all files.