Hack #16 -> Cut Command

Cut command can be used to display only specific columns from a text

file or other command outputs.

The following are some of the examples.

Display the 1st field (employee name) from a colon delimited file

$ cut -d: -f 1 names.txt

Emma Thomas

Alex Jason

Madison Randy

Sanjay Gupta

Nisha Singh

Display 1st and 3rd field from a colon delimited file

$ cut -d: -f 1,3 names.txt

Emma Thomas:Marketing

Alex Jason:Sales

Madison Randy:Product Development

Sanjay Gupta:Support

Nisha Singh:Sales

Display only the first 8 characters of every line in a file

$ cut -c 1-8 names.txt

Emma Tho

Alex Jas

Madison

Sanjay G

Nisha Si

Misc Cut command examples

• cut -d: -f1 /etc/passwd Displays the unix login names for all the

users in the system.

• free | tr -s ‘ ‘ | sed ‘/^Mem/!d’ | cut -d” ” -f2 Displays the

total memory available on the system.

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Hack #15 -> Uniq Command

Uniq command is mostly used in combination with sort command, as

uniq removes duplicates only from a sorted file. i.e In order for uniq to

work, all the duplicate entries should be in the adjacent lines. The

following are some common examples.

1. When you have an employee file with duplicate entries, you can do

the following to remove duplicates.

$ sort namesd.txt | uniq

$ sort –u namesd.txt

2. If you want to know how many lines are duplicates, do the following.

The first field in the following examples indicates how many duplicates

where found for that particular line. So, in this example the lines

beginning with Alex and Emma were found twice in the namesd.txt file.

$ sort namesd.txt | uniq –c

2 Alex Jason:200:Sales

2 Emma Thomas:100:Marketing

1 Madison Randy:300:Product Development

1 Nisha Singh:500:Sales

1 Sanjay Gupta:400:Support

3. The following displays only the entries that are duplicates.

$ sort namesd.txt | uniq –cd

2 Alex Jason:200:Sales

2 Emma Thomas:100:Marketing

Hack #14 -> Sort Command

Sort command sorts the lines of a text file. Following are several

practical examples on how to use the sort command based on the

following sample text file that has employee information in the format:

employee_name:employee_id:department_name.

$ cat names.txt

Emma Thomas:100:Marketing

Alex Jason:200:Sales

Madison Randy:300:Product Development

Sanjay Gupta:400:Support

Nisha Singh:500:Sales

Sort a text file in ascending order

$ sort names.txt

Alex Jason:200:Sales

Emma Thomas:100:Marketing

Madison Randy:300:Product Development

Nisha Singh:500:Sales

Sanjay Gupta:400:Support

Sort a text file in descending order

$ sort -r names.txt

Sanjay Gupta:400:Support

Nisha Singh:500:Sales

Madison Randy:300:Product Development

Emma Thomas:100:Marketing

Alex Jason:200:Sales

Sort a colon delimited text file on 2nd field (employee_id)

$ sort -t: -k 2 names.txt

Emma Thomas:100:Marketing

Alex Jason:200:Sales

Madison Randy:300:Product Development

Sanjay Gupta:400:Support

Nisha Singh:500:Sales

Sort a tab delimited text file on 3rd field (department_name) and

suppress duplicates

$ sort -t: -u -k 3 names.txt

Emma Thomas:100:Marketing

Madison Randy:300:Product Development

Alex Jason:200:Sales

Sanjay Gupta:400:Support

Sort the passwd file by the 3rd field (numeric userid)

$ sort -t: -k 3n /etc/passwd | more

root:x:0:0:root:/root:/bin/bash

bin:x:1:1:bin:/bin:/sbin/nologin

daemon:x:2:2:daemon:/sbin:/sbin/nologin

adm:x:3:4:adm:/var/adm:/sbin/nologin

lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin

Sort /etc/hosts file by ip-address

$ sort -t . -k 1,1n -k 2,2n -k 3,3n -k 4,4n /etc/hosts

127.0.0.1 localhost.localdomain localhost

192.168.100.101 dev-db.thegeekstuff.com dev-db

192.168.100.102 prod-db.thegeekstuff.com prod-db

192.168.101.20 dev-web.thegeekstuff.com dev-web

192.168.101.21 prod-web.thegeekstuff.com prod-web

Combine sort with other commands

• ps –ef | sort : Sort the output of process list
• ls -al | sort +4n : List the files in the ascending order of the filesize.

i.e sorted by 5th filed and displaying smallest files first.

• ls -al | sort +4nr : List the files in the descending order of the

file-size. i.e sorted by 5th filed and displaying largest files first.

Hack #13 -> Xargs Command

Xargs is a very powerful command that takes output of a command and

pass it as argument of another command.

The following are some practical examples on how to use xargs

effectively.

1. When you are trying to delete too many files using rm, you may get

error message: /bin/rm Argument list too long – Linux. Use xargs to avoid

this problem.

find ~ -name ‘*.log’ -print0 | xargs -0 rm -f

2. Get a list of all the *.conf file under /etc/. There are different ways to

get the same result. Following example is only to demonstrate the use of

xargs. The output of the find command in this example is passed to the

ls –l one by one using xargs.

# find /etc -name “*.conf” | xargs ls –l

3. If you have a file with list of URLs that you would like to download, you

can use xargs as shown below.

# cat url-list.txt | xargs wget –c

4. Find out all the jpg images and archive it.

 

# find / -name *.jpg -type f -print | xargs tar -cvzf images.tar.gz

5. Copy all the images to an external hard-drive.

# ls *.jpg | xargs -n1 -i cp {} /external-harddrive/directory

Hack #12 -> Change the Case

Convert a file to all upper-case

$ cat employee.txt

100 Jason Smith

200 John Doe

300 Sanjay Gupta

400 Ashok Sharma

$ tr a-z A-Z < employee.txt

100 JASON SMITH

200 JOHN DOE

300 SANJAY GUPTA

400 ASHOK SHARMA

Convert a file to all lower-case

$ cat department.txt

100 FINANCE

200 MARKETING

300 PRODUCT DEVELOPMENT

400 SALES

$ tr A-Z a-z < department.txt

100 finance

200 marketing

300 product development

400 sales