Linux/Unix Tutorial for Beginners - cat command , grep command
This tutorial comprises of brief description with real time output of the cat command and grep command
Th cat command is used for viewing contents of a file
The grep command is used for searching keyword/s in files.
The various options/combinations of cat commands are as follows:-
1.) cat filename -- displays contents of a file
2.) cat file1 file2 -- displays contents of multiple files
3.) cat file1 greater_than_sign file2 -- copy contents of file 1 and overwrite it on top of file2
4.) cat -n filename -- displays the contents of the files by appending line numbers
5.) cat file1 greater_than_signgreater_than_sign file2 -- append contents of file 1 to that of file2.
6.) tac file -- displays the contents of file in a reverse order
7.) cat greater_than_sign filename -- creates a file with the name provided in the command and then allows to enter contents for the file in the immediate next line using the same command.
8.) cat filename | more -- Allows to display contents of a huge file in a page by page format and scrolling only happens down the page(unidirectional), this is a bit slower than the less option.
9.) cat filename | less -- Allows to display contenst of a huge file where the user can scroll both up and down as required.
10.) cat file1 file2 file3 greater_than_sign file4 -- Allows contents of multiple files to be redirected to a particular file.
The various options/combinations of grep command are as follows:-
1.) grep keyword path_of_file -- displays the lines of the file at places where the keyword is available.
2.) grep -v keyword path_of_file -- displays the lines of the files at places where the keyword is NOT available.
3.) command output | grep keyword -- searches for a keyword in lines of output of a command it is used with
Ex- ps -ef | grep java
4.) grep -r keyword path_to_be searched -- searches for a keyword recursively within the provided path and doesn't include any sym-links.
5.) grep -R keyword path_to_be searched -- searches for a keyword recursively within the provided path and includes any sym-links.
6.) grep -i path_of_file --searches for a keyword irrespective of the case of the keyword.
7.)grep -n path_of_file -- this option includes line numbers to output of grep command
8.)grep -w keyword path_of_file -- to match for words of the file where the keyword is same as the matched wor.
9.) grep -c keyword path_of_file -- this shows the count of matching lines at the provided path_of_file
10.) grep -E 'keyword1|keyword2' path_of file -- this option is used for searching multiple files.
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