Power Tools

 Few of tools which are very important for day to day use.

  - Head

  - Tail

  - Grep

  - cut

  - wc

  - sort

  - diff

  - sdiff

  - aspell

  - tr

  - sed

  - awk

  

Head

 

- output the first part of files.Head without a number prints ten lines by default.

                                               

Syntax:  head [OPTION]... [FILE]...

                                               

examples:

1. First ten lines of a file.

                                                                                               

head -n 10 file1.txt                                                                                                    

cat file1.txt|head -n 10

                                                                                                                       

2. First ten characters of a file.

                                                     

head -c 10 file1.txt

cat file1.txt|head -c 10

                                                                                               

                                                 

 Tail

 

-  output the last part of files.Tail without a number prints ten lines by default.

                                   

Syntax: tail [OPTION]... [FILE]...

                                               

examples:

1. First ten lines of a file.

                                                                                                                                   

                                                                                                                                           tail -n 10 file1.txt

cat file1.txt|tail -n 10

2. First ten character of a file.

                                                                                                                                   

                                                                                                                                                tail -c 10 file1.txt

                                                                                                                                                cat file1.txt|tail -c 10

                                                                                                                                                                                   

3.For a output appended data as the file grows.

                                                                                                                                   

                                                                                                                                                tail -f file1.txt

 

  Grep

- print lines matching a pattern.

                                               

Syntax:

grep [OPTIONS] PATTERN [FILE...]

grep [OPTIONS] [-e PATTERN | -f FILE] [FILE...]

                                                                                                             

examples:

                                                                                     

1. To get a word from a file.

                                                                                                                                               

cat file1.txt|grep  "ost"

grep     "ost" file1.txt

                                                                                                                                                           

2. To get a word irrespective of case.

                                                                                                                                   

cat file1.txt|grep -i "ost"

grep "ost" file1.txt

                                                                                                                                                                                               

3.To select only those lines containing matches that form whole words.

                                                                                                                                               

cat file1.txt|grep -w "ost"

grep -w "ost" file1.txt

                                                                                                                                   

4.Print a count of matching lines for each input file.

                                                                                                                                   

cat file1.txt|grep -c "ost"

grep -c "ost" file1.txt

                                                                                                                                               

Few more options to work on:

                                                                                                           

- -A, --after-context=NUM   print NUM lines of trailing context.

- -B, --before-context=NUM  print NUM lines of leading context.

- -C, --context=NUM         print NUM lines of output context.

 - -x, --line-regexp         force PATTERN to match only whole lines.

- -V, --version             print version information and exit

                                                                                               

 Cut

- cut - remove sections from each line of files

                                                           

Syntax: cut [OPTION]... [FILE]...

                                                           

examples:

                                                           

1. To get first 10 characters of a line.

                                                                                                                                               

cut -c1-10 file1.txt

cat file1.txt|cut -c1-10

                                                                                                                                                                       

 2. Suppose the fields are seperated by delimiter.

                                                                                                                                                   

To take the first field in the /etc/passwd file

                                                                                                                                                    

                                                                                                                                                     cat /etc/passwd|cut -f 1 -d :                  

                                                                                                                                                    

                                                                                                                                                     This will extract the first field with delimiter as ":"

                                                                                                                                                    

                                                                                                                                                    

                                                                                                                                                    

 wc

- wc - print the number of bytes, words, and lines in files.

                                                                       

Syntax: wc [OPTION]... [FILE]...

                                   

examples:

                                                           

1. To get the byte count

                                                                                                                                               

wc -c file1.txt

                                                                                                                                                                                   

                                                                                                                                               

2. To print the character count.

                                                                                                                                               

                                                                                                                                                                                    wc -m file1.txt

                                                                                                                                                                                   

3. To print the newline counts.

                                                                                                                                               

                                                                                                                                                                                    wc -l file1.txt

                                                                                                                                                                                   

4. To print the length of the longest line.

                                                                                                                                                           

                                    wc -L file1.txt

                                                                                                                                                                                   

 Sort

- sort - sort lines of text files.

                                   

1.  To sort according to dictionary order.

                                                                                                                                   

sort -d file1.txt

                                                                                                                                                                                   

2. To sort ignoring the case.

                                                                                                                                   

sort -f file1.txt

                                                                                                                                                                                   

  3. To sort according to months.

                                                                                                                                   

sort -M file1.txt

                                                                                                                                                                                   

4. To sort numerically.

                                                                                                                                   

sort -n file1.txt

                                                                                                                                                                                   

5. To reverse sort.

                                                                                                                                   

sort -r file1.txt

                                                                                                                                   

                                                                                                                                   

 aspell                                                                                                             

                                                                                                                                                                                   

                                               

- aspell - For spell check

                                               

1. To interactivly check the spellings.

                                                                                                                                               

                                                                                                                                                aspell check file1.txt

                                                                                                                                                                       

                                                                                                                                                aspell check < file2.txt

                                                                                                                                                                       

tr

- tr - Used for changing the the case or translating.

                                               

tr '[A-Z]' '[a-z]' < file1.txt

                                                                                                                                   

This will change all the characters in the file "file1.txt" to capital letters.

                                                                                                                                   

sed

-sed - stream editior.

                                               

1. change words in a file.

                                                                                                           

                                                                                                                                                sed 's/ost/OST/g' file1.txt

                                                                                                                                                sed '1,10s/ost/OST/g' file1.txt

                                                                                                                                                sed '/ost/,/OST/s/class/tutor/g' file1.txt

                                                                                                                                               

awk

- awk - editor

                                   

1.Print the first field of the  file.

                                                                                                             

                                                                                                                                                cat file|awk '{print $1}'

                                                                                                                                               

2.Print the first fields of a passwd file.

                                                                                                             

cat /etc/passwd|awk -F: '{print $1}'