Now days Linux is growing very fast compare to other operating systems, so all application getting developed in cross platform, so that time, developer are required to work on linux. Not an administrator level but some random commands should aware to work on linux. Here we have listed linux commands developer should know.
Following are the list of ten commands you will learn about in this post
man
The first command you should learn in Linux is “man”. Using this command you can get the usage and description of all Linux commands. For example, if you want to know about “ls” command and its options, just execute “man ls” command in the terminal to list its usage and description.
Syntax:
# man <command name>
# man ls
# man ls
LS(1) User Commands LS(1)
NAME
ls – list directory contents
SYNOPSIS
ls [OPTION]… [FILE]…
DESCRIPTION
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor –sort is speciâ
fied.
Mandatory arguments to long options are mandatory for short options
too.
-a, –all
do not ignore entries starting with .
Touch, cat and less
Touch command is used to create any type of file in Linux systems with “0” size. As a developer, when working with Linux you might want to create files in the server. You can make use of touch command to do that.
Syntax:
# touch <filename>
# touch any.txt
root@foxutech:~# touch any.txt
root@foxutech:~# ls
any.txt
Cat command is used to view the contents of a file. You cannot edit the contents of the file using cat. It just gives a view of the file.
Syntax: cat <filename>
# cat anyname.txt
Less command also gives the view of a file. less is very fast and you can use the arrow keys to scroll up and down to know the start and end of the file. There is also “more” command, which is used to view the file but it allows only forward scrolling using “enter” key. It doesn’t support backward scrolling.
Syntax: less <filename>
more <filename>
# less anyname.txt
# more anyname.txt
sort
Sort command is helpful to sort/order lines in text files. You can sort the data in text file and display the output on the screen, or redirect it to a file. Based on your requirement, sort provides several command line options for sorting data in a text file.
Sort Command Syntax:
# sort [-options]
# cat test
aa aa zz
aa aa ff
aa aa tt
aa aa kk
In the above example, second column has the names. So if you want to sort the names alphabetically use “-k” flag with the column location. It would be “-k2”.
# sort -k3 test
aa aa ff
aa aa kk
aa aa tt
aa aa zz
The following sort command sorts lines in test file on the 3rd word of each line and displays sorted output.
# sort -k3 test
aa aa ff
aa aa kk
aa aa tt
aa aa zz
# cat test
aa aa zz
aa aa ff
aa aa tt
aa aa kk
Grep:
grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus (-) is given as file name) for lines containing a match to the given PATTERN. By default, grep prints the matching lines.
In addition, two variant programs egrep and fgrep are available. egrep is the same as grep -E. fgrep is the same as grep -F. Direct invocation as either egrep or fgrep is deprecated, but is provided to allow historical applications that rely on them to run unmodified.
Syntax: grep “<search string>” <filename>
grep “aa” test
root@foxutech:~# grep “aa” test
aa aa zz
aa aa ff
aa aa tt
aa aa kk
The above command gives the output including the sub-string. If you want to search for individual words, you need to add “-i” flag to the grep command. Also you can search for a string or a pattern in multiple files using a single grep command. For example,
# grep “dennis” test1.txt test2.txt test3.txt
You can also use regular expressions for matching the string.
cut
Cut command is used for extracting a portion of a file using columns and delimiters. If you want to list everything in a selected column, use the “-c” flag with cut command. For example, lets select the first two columns from our test.txt file.
cut -c1-2 test.txt
root@foxutech:~# cut -c1-2 test.txt
1
10
45
4
7
58
If you want to extract specific strings from a file, you can used the delimiter “-d” flag and “-f” flag to select the field. For example, if you want to extract all the names from our test.txt file you can use the following command.
cut -d’ ‘ -f2 test.txt
root@foxutech:~# cut -d’ ‘ -f2 test.txt
mike
lucy
Dave
dennis
Megan
Mathew
The following example extracts the users from /etc/passd file using ‘:” delimiter.
cut -d’:’ -f1 /etc/passwd
sed
sed is a text-editor which can perform editing operations in a non-interactive way. Sed command gets its input from a standard input or a file to perform the editing operation on a file. Sed is a very powerful utility and you can do a lot of file manipulations using sed. I will explain the important operation you might want to do with text file.
I you want to replace a text in a file by searching it in a file, you can use the sed command with substitute “s” flag to search for the specific pattern and change it.
Syntax: sed ‘s/<old-word>/<new-word>/’ test
For example, lets replace “aa” in test file to “bb”
root@foxutech:~# sed ‘s/aa/bb/’ test
bb aa zz
bb aa ff
bb aa tt
bb aa kk
In the above example we used “/” as a delimiter for string substitution. You can use any character as a delimiter for substitution. For example, if you want to make changes to a url, you need to have a different delimiter because the url already have slashes. So you can substitute like the following.
echo “http://www.foxutech.us/main.html” | sed ‘s_us/main_com/index_’
root@foxutech:~# echo “http://www.foxutech.us/main.html” | sed ‘s_us/main_com/index_’
http://www.foxutech.com/index.html
You can also replace a line by matching a string pattern in the line. “-c” flag is used for replacing text using sed. Let’s replace the first line in our test.txt file using the following command.
tar
tar command is used to create and extract archive files. “-cf” and “-xf” flags are used for creating and extracting archives.
Syntax: tar <options> <archive-name> <file/folder name>
Let’s create a tar archive out of test.txt file
root@foxutech:~# tar -cf test.tar test.txt
root@foxutech:~# ls
test.tar test.txt
Let’s extract the test.tar archive to the destination folder “demo” using “-C” flag.
root@foxutech:~# tar -xf test.tar -C /root/test/
root@foxutech:~# cd test/
root@foxutech:~/test# ls
test.txt
find
find command is used for finding files. You can find the files using its name with “-name” flag.
root@foxutech:/home/ubuntu# cd ~
root@foxutech:~# find -name test
./demo/test
./test
You can also find folder using its name by using”/ -name” flag.
root@foxutech:~# find / -name passwd
/etc/cron.daily/passwd
/etc/pam.d/passwd
/etc/passwd
/usr/share/test/overrides/passwd
diff
diff command is used to find the difference between two files. Diff command analyses the files and prints the lines which are different. Let’s say we have two files test and test1. You can find the difference between the two files using the following command.
Syntax: diff <filename1> <filename2>
diff test.txt test1.txt
root@foxutech:~# diff p1.pl p1.pl.in
19c19
< use constant DEBUG_LOG_PATH => ‘${prefix}/var’ ;
—
> use constant DEBUG_LOG_PATH => ‘@LOGDIR@’ ;
Uniq
uniq command is used for filtering out the duplicate line in a file.
Syntax: uniq
uniq test.txt
root@foxutech:~# uniq test
aa aa zz
aa aa ff
aa aa tt
aa aa kk
chmod
chmod command is used for changing the read/write/execute permissions of a file. Permissions are represented in numbers as follows.
4 – read permission
2 – write permission
1 – execute permission
0 – no permission
To give all permissions on test.txt file, you can use the following chmod command.
chmod 755 test.txt
