grep - it is a command line utility for searching plain text data sets for lines matching a regular expression. Grep was developed by Ken Thompson.
syntax: grep [options] pattern [files]
Options
Option
|
Description
|
-b
|
Display the block
number at the beginning of each line.
|
-c
|
Display the number of
matched lines.
|
-h
|
Display the matched
lines, but do not display the filenames.
|
-i
|
Ignore case
sensitivity.
|
-l
|
Display the filenames,
but do not display the matched lines.
|
-n
|
Display the matched
lines and their line numbers.
|
-s
|
Silent mode.
|
-v
|
Display all lines that
do NOT match.
|
-w
|
Match whole word.
|
e.g grep imocha student.txt
above code will search all the line which contain 'imocha' in the file student.txt
here the grep is case sensitive. if you want to ignore then use -i
e.g. grep -i imocha student.txt
the above code will find the word imocha and IMOCHA in the file student.txt
Options in grep
egrep - it is an acronym for " Extended Global Regular Expression Print". it is used to scan the file line by line and it returns the pattern matching a given expression.
syntax: egrep <flag> '< regular expression>' <filename>
flag: -c ---- counting the number of successful matches and not printing the actual matches.
-i ---- make the search case insensitive.
-n ---- to print the number before each match printout.
-v ---- returns the line which don't match.
ls - it is use to list the files or directory
rm - it is used to remove file or directory
to remove a file
rm filename
to remove a directory
rm -r directoryname
sed - it is an stream editor, but it is unlike others because it is not a screen oriented,centos
it is not interactive.
it is not interactive.
This means we have to insert the commands to be executed on the data at the command line or in a script to pe processed.
sed accept series of commands and execute them on a file ( or set of files).
How sed works
The sed utility works by sequentially reading a file, line by line, into the memory. It then performs all actions specified for the line and places the line back in memory to dump to the terminal with the requested changes made. After all actions have taken place to this one line, it reads the next line of the file and repeats the process until it is finished with the file.
syntax: sed [option] '[command]' [filename]
example: sed 's/mail/email/' filename
here all the 'mail' word will be replace by 'email' word in the file.
sed accept series of commands and execute them on a file ( or set of files).
How sed works
The sed utility works by sequentially reading a file, line by line, into the memory. It then performs all actions specified for the line and places the line back in memory to dump to the terminal with the requested changes made. After all actions have taken place to this one line, it reads the next line of the file and repeats the process until it is finished with the file.
syntax: sed [option] '[command]' [filename]
example: sed 's/mail/email/' filename
here all the 'mail' word will be replace by 'email' word in the file.
ls -l | sort -k1
it will will sort the list of files based on first column (-k1)
tee - it is used to read the standard input and write it to standard output as well as into one or more files.
ls | tee filename
wc - it is use to count the number of lines,word or characters in a file.
Suppose if we execute the command as
wc filename
5 10 85 filename
5 ---- number of lines in the file
10 ---- number of word in the file
85 ---- number of characters in the file.
if you want only the line or only the character or only the words then
wc -c filename ---- for characters
wc -l filename ----- for line number
wc -w filename ---- for words
1. How to find the occurrence of a word in a file?
grep -c "search_word" filename
2. List the lines in file.txt containing the word 'hello'
egrep -i 'hello' file.txt
3. How to display only the directories in linux?
ls -l | egrep '^d'
^d -- it is used to find the character d at the beginning of each line.
if you execute ls -l it display like
so if we execute the ls -l | egrep '^d' it will display only the lines which having 'd' as a first character in each line.
4. How to list only the files?
ls -l | egrep -v '^d'
or
ls -al | grep '^-'
this will list all the files including the hidden files
5. How to rename a directory?
mv oldfilename newfilename
6. How to display the 5th line of a file?
head -5 filename | tail -1
7. How to delete a line from a file?
sed -i '3d' filename
8. How to remove the footer from a file?
sed -i '$ d' filename
9. How to get the 5th word of a line in Unix?
awk '{print $5}' filename
10 Print the 2nd and 5th line from a file.
sed -n '2p;5p' filename
or
awk 'NR==2|| NR==5' filename
11 Print alternate lines of a file
awk 'NR%2==0' filename
or
cat filename | awk 'NR%2==0'
12. Display the last column form a file
cat filename | rev | awk '{print $1}'| rev
or
cat filename | rev | cut -f1 -d ' '| rev
13. Replace the nth line by a new line
sed -i '' '4d' filename
sed -i'' ' 4i new_line ' filename
where 4. is the line number
d means delete
i means insert
14. Convert all the text in a file into uppercase letter.
awk '{ print toupper ($0) }' filename > new_filename
or
dd if=filename of=new_filename conv=ucase
or
tr '[:lower:]' '[:upper:]' <filename> new_filename
15. Convert all the text in a file into lowercase letter.
awk '{ print tolower($0) }' filename > new_filename
or
dd if=filename of=new_filename conv=lcase
or
tr '[:upper:]' '[:lower:]' <filename> new_filename
or
y=$(<filename)
echo "${y^^)"
15. Find the newest file in the directory.
ls -ltr | tail -1
15.1. Find the newest directory
ls -ltr | grep ^d | tail -1
16. What is difference bewteen $#, $@ and $?
$# it is used to returned the number of argument (parameter)
$@ it is used to get the parameters passed
$? it is used to find the status of the previous executed command. if the command was success full then it will return otherwise it will return other number.
17. Print the content of a file with the line number
cat -n filename
or
grep -n '^' filename
or
awk -F':' '{ print NR, $1} filename
18. Print a listing of files in directory.
ls | grep -v "files">files.txt
19. How to find the difference between two files?
diff file1 file2
or
sdiff file1 file2
20. Count the number of files in a directory.
ls | wc -l
21. List the files which 5 days old.
find . -name "*" -mtime -5 -print
22. List all the .csv files in a directory
find . -name "*.csv"
23. How to insert a new line after 4th line in a file
sed '4 a\Your line' filename
24. Find the file based on the month
ls -l | grep monthname
here filename should be Jan, Feb or first character or the month like J,F,M etc.
25. Convert tab delimited file into comma delimited file
sed 's/t\/,/g' input_filename>output_filename
26. Print a lower case string into uppercase
echo "hello" | awk '{print toupper($1)}'
27. Display a file by removing white spaces.
cat <filename> | sed 's/ //g'
28. Create a file by removing unwanted string from an existing file.
cat <filename> | sed 's/string_to_remove//g' > <newfilename> .
29. Count he blank line in a file
grep -cPv '\S' <filename>
-c is to count
-v is to find the blank line
-P '\S' is to find the which has non-space
30. Print the file by removing blank line
grep -P '\S' <filename>
31. Print the file by removing blank line
tail -n+2 <filename> or sed -n '2,$p' emp
32. Calculate the difference of two time
startTime=$(date +%s) endTime=$(date +%s) differentTime=$(($endTime - $startTime)) printf 'Time difference %dh:%dm:%ds\n' $(($differentTime/3600)) $(($differentTime%3600/60)) $(($differentTime%60))
diff file1 file2
or
sdiff file1 file2
20. Count the number of files in a directory.
ls | wc -l
21. List the files which 5 days old.
find . -name "*" -mtime -5 -print
22. List all the .csv files in a directory
find . -name "*.csv"
23. How to insert a new line after 4th line in a file
sed '4 a\Your line' filename
24. Find the file based on the month
ls -l | grep monthname
here filename should be Jan, Feb or first character or the month like J,F,M etc.
25. Convert tab delimited file into comma delimited file
sed 's/t\/,/g' input_filename>output_filename
26. Print a lower case string into uppercase
echo "hello" | awk '{print toupper($1)}'
27. Display a file by removing white spaces.
cat <filename> | sed 's/ //g'
28. Create a file by removing unwanted string from an existing file.
cat <filename> | sed 's/string_to_remove//g' > <newfilename> .
29. Count he blank line in a file
grep -cPv '\S' <filename>
-c is to count
-v is to find the blank line
-P '\S' is to find the which has non-space
30. Print the file by removing blank line
grep -P '\S' <filename>
31. Print the file by removing blank line
tail -n+2 <filename> or sed -n '2,$p' emp
32. Calculate the difference of two time
startTime=$(date +%s) endTime=$(date +%s) differentTime=$(($endTime - $startTime)) printf 'Time difference %dh:%dm:%ds\n' $(($differentTime/3600)) $(($differentTime%3600/60)) $(($differentTime%60))
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