There are many commands which help to look at the contents of a file. Now we’ll look at some of the commands like head, tac, cat, less & more and strings.
Head
The ‘head’ command displays the starting content of a file. By default, it displays starting 10 lines of any file.
head {filename}
// -n option followed by an integer specifying the number of lines to be shown.
head -n {number} {filename}
// show content of multiple files to n line
head -n {number} {filename1} {filename2}
// -c option allows to print a specific number of bytes
head -c {number} {filename}
// show content of multiple files to number of bytes
head -c {number} {filename1} {filename2}
Examples
head {filename1} {filename2}…
folaukaveinga@Folaus-MacBook-Pro-3 files % head test.txt test2.txt ==> test.txt <== test test1 sdf ewr sdfb dcxzv xcv x ==> test2.txt <== wer qwe rq wer qwe rqwe r qwe rq wer
head -n {filename1} {filename2}…
folaukaveinga@Folaus-MacBook-Pro-3 files % head -n 5 test.txt test test1 sdf ewr folaukaveinga@Folaus-MacBook-Pro-3 files % head -n 5 test.txt test2.txt ==> test.txt <== test test1 sdf ewr ==> test2.txt <== wer qwe rq wer qwe
head -c {number} {filename1} {filename2}…
folaukaveinga@Folaus-MacBook-Pro-3 files % head -c 10 test.txt test test1% folaukaveinga@Folaus-MacBook-Pro-3 files % head -c 10 test.txt test2.txt ==> test.txt <== test test1 ==> test2.txt <== wer qwe rq%
Tail
Linux tail command is used to display the last ten lines of one or more files. Its main purpose is to read the error message. By default, it displays the last ten lines of a file. Additionally, it is used to monitor the file changes in real-time. The default use of the tail command displays the last ten lines of the files.
tail -n {number} {filename1} {filename2}…
Prints the last ‘n’ lines. n is mandatory to be specified in command otherwise it displays an error
folaukaveinga@Folaus-MacBook-Pro-3 files % tail -n 5 test.txt asdf asd fasd fasd
tail -c {number} {filename1} {filename2}…
The ‘-c’ option displays the specified number of content for bytes from the last line.
folaukaveinga@Folaus-MacBook-Pro-3 files % tail -c 10 test.txt asd fasd
tail -f {number} {filename1} {filename2}…
This option is mainly used by system administration to monitor the growth of the log files written by many Unix program as they are running. This option shows the last ten lines of a file and will update when new lines are added. As new lines are written to the log, the console will update with the new lines.
folaukaveinga@Folaus-MacBook-Pro-3 files % tail -f test.txt f sad f i asdf asdf asd fasd fasd
Cat
The ‘cat’ command can be used to display the content of a file, copy content from one file to another, concatenate the contents of multiple files, display the line number, display $ at the end of the line, etc.
cat {filename}
display all content of a file
folaukaveinga@Folaus-MacBook-Pro-3 files % cat test.txt test test1 sdf ewr sdfb dcxz fasd
cat > {filename}
create a file
folaukaveinga@Folaus-MacBook-Pro-3 files % cat > test1.txt easdf asd fasd fasdf ^C folaukaveinga@Folaus-MacBook-Pro-3 files % head test1.txt easdf asd fasd fasdf
cat >> {filename}
>> appends input to the end of the file
folaukaveinga@Folaus-MacBook-Pro-3 files % cat >> test1.txt test123 sdfsdf^C
cat {filename1} {filename2}… > {newfilename}
copy contents of one file(filename1} to another file {newfilename}
with (-) a new line will be inserted while concatenating multiple files by using a hyphen (-).
folaukaveinga@Folaus-MacBook-Pro-3 files % cat test1.txt > test4.txt folaukaveinga@Folaus-MacBook-Pro-3 files % ls test test.txt test1.txt test2.txt test3.txt test4.txt folaukaveinga@Folaus-MacBook-Pro-3 files % head test4.txt easdf asd fasd fasdf test123 folaukaveinga@Folaus-MacBook-Pro-3 files % cat test1.txt test2.txt > test5.txt // add new line \n to the end of test.txt content folaukaveinga@Folaus-MacBook-Pro-3 files % cat - test1.txt test2.txt > test5.txt
cat -n {filename}
-n shows the number line
folaukaveinga@Folaus-MacBook-Pro-3 files % cat -n test5.txt
1 easdf
2 asd
3 fasd
4 fasdf
5 test123
6 123
7 123
8 s
9 df
10 asd
cat -e {filename}
The ‘cat-e’ option displays a ‘$’ sign at the end of every line. This is very useful when you are looking for the end of a line.
folaukaveinga@Folaus-MacBook-Pro-3 files % cat -e test.txt test$ test1$ sdf$ ewr$ sdfb$ dcxzv$ $
cat {filename} | more
This gives you an option to paginate what to display.
cat test.txt | more
sort {filename}
Sort content of file alphabetically.
folaukaveinga@Folaus-MacBook-Pro-3 Downloads % sort test.txt as asd asd asd asd asd asdf asdf