comm command in Linux with examples

comm compare two sorted files line by line and write to standard output; the lines that are common and the lines that are unique.

Suppose you have two lists of people and you are asked to find out the names available in one and not in the other, or even those common to both. comm is the command that will help you to achieve this. It requires two sorted files which it compares line by line.

Before discussing anything further first let’s check out the syntax of comm command:

Syntax:

$comm [OPTION]... FILE1 FILE2

◉ As using comm, we are trying to compare two files therefore the syntax of comm command needs two filenames as arguments.

◉ With no OPTION used, comm produces three-column output where first column contains lines unique to FILE1 ,second column contains lines unique to FILE2 and third and last column contains lines common to both the files.

◉ comm command only works right if you are comparing two files which are already sorted.

Example: Let us suppose there are two sorted files file1.txt and file2.txt and now we will use comm command to compare these two.

// displaying contents of file1 //
$cat file1.txt
Apaar
Ayush Rajput
Deepak
Hemant

// displaying contents of file2 //
$cat file2.txt
Apaar
Hemant
Lucky
Pranjal Thakral

Now, run comm command as:

// using comm command for
comparing two files //
$comm file1.txt file2.txt
                Apaar
Ayush Rajput
Deepak
                Hemant
        Lucky
        Pranjal Thakral

The above output contains of three columns where first column is separated by zero tab and contains names only present in file1.txt ,second column contains names only present in file2.txt and separated by one tab and the third column contains names common to both the files and is separated by two tabs from the beginning of the line.
This is the default pattern of the output produced by comm command when no option is used .

Options for comm command:

1. -1: suppress first column(lines unique to first file).
2. -2: suppress second column(lines unique to second file).
3. -3: suppress third column(lines common to both files).
4. – -check-order: check that the input is correctly sorted, even if all input lines are pairable.
5. – -nocheck-order: do not check that the input is correctly sorted.
6. – -output-delimiter=STR: separate columns with string STR
7. – -help: display a help message, and exit.
8. – -version: output version information, and exit.

Note: The options 4 to 8 are rarely used but options 1 to 3 are very useful in terms of the desired output user wants.

Using comm with options

1. Using -1 ,-2 and -3 options: The use of these three options can be easily explained with the help of example :

//suppress first column using -1//
$comm -1 file1.txt file2.txt
         Apaar
         Hemant
 Lucky
 Pranjal Thakral

//suppress second column using -2//
$comm -2 file1.txt file2.txt
        Apaar
Ayush Rajput
Deepak
        Hemant

//suppress third column using -3//
$comm -3 file1.txt file2.txt           
Ayush Rajput
Deepak     
        Lucky
        Pranjal Thakral

Note that you can also suppress multiple columns using these options together as:

//...suppressing multiple columns...//

$comm -12 file1.txt file2.txt
Apaar
Hemant

/* using -12 together suppressed both first
and second columns */

2. Using – -check-order option: This option is used to check whether the input files are sorted or not and in case if either of the two files are wrongly ordered then comm command will fail with an error message.

$comm - -check-order f1.txt f2.txt

The above command produces the normal output if both f1.txt and f2.txt are sorted and it just gives an error message if either of the two files are not sorted.

3. Using – -nocheck-order option: In case if you don’t want to check whether the input files are sorted or not, use this option. This can be explained with the help of an example.

//displaying contents of unsorted f1.txt//

$cat f1.txt
Parnjal
Kartik

//displaying contents of sorted file f2.txt//

$cat f2.txt
Apaar
Kartik

//now use - -nocheck-order option with comm//

$comm - -nocheck-order f1.txt f2.txt
Pranjal
        Apaar
                Kartik

/*as this option forced comm not to check
 the sorted order that's why the output
comm produced is also
not in sorted order*/

4 . – -output-delimiter=STR option: By default, the columns in the comm command output are separated by spaces as explained above. However, if you want, you can change that, and have a string of your choice as separator. This can be done using the –output-delimiter option. This option requires you to specify the string that you want to use as the separator.

Syntax:

$comm - -output-delimiter=STR FILE1 FILE2

EXAMPLE:

//...comm command with - -output-delimiter=STR option...//

$comm - -output-delimiter=+file1.txt file2.txt
++Apaar
Ayush Rajput
Deepak
++Hemant
+Lucky
+Pranjal Thakral

/*+ before content indicates content of
second column and ++ before content
indicates content of third column*/

So,that’s all about comm command and its options.

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TDC teaches how to deliver a vibrant interactive experience

How does a conference make the transition to virtual participation in the age of the COVID-19 virus? And suppose you have less than two months to do so?

As social distancing loomed as a dire necessity in February and March 2020, many organizations simply threw up their hands and canceled their conferences. But some were prepared to put their offering online. The major Brazilian organization "The Developer's Conference" is particularly worth examining for their online work. Building on previous experiences with hybrid conferences (mixed on-site and online), they rethought everything about what they were doing and produced a unique experience that they are now teaching others to reproduce.

The amount of interaction among speakers, sponsors, and attendees at TCDOnline was a much as ever, perhaps more so. And the 30 staff gracefully handled 6,750 attendees.

This article, based on a conversation I had with event director Yara Senger, will show how they did it.

TDC started in 2007. As early as 2009, they offered a cost-free online component along with their regular on-site conference. But the online component was modest: just video feeds of the speakers. Attendance was growing gradually over the years, and toward the end was about 11,000 on-site attendees with an additional 5,000 to 6,000 online participants.

Organizers could tell that there was not much interaction by online participants. In particular, the online participants offered little benefit to sponsors, whose satisfaction is crucial to make conferences work financially. If they just extended this format to an all-virtual conference, the experience would not be particularly positive. They worked from the premise that people need to feel comfortable with every aspect of an online experience in order to attract them year after year.

So the organizers started from the ground up, producing a very different kind of conference. Some of the important changes follow.

◉ The traditional experience of being greeted when you enter the door of an event was reproduced by banks of employees who approached every attendee as they logged into the conference. Every question received a prompt answer. If someone couldn't get into a room for some technical reason, they could get help in a chat.

◉ Video was available, so that you could see the people you were talking to. I asked Senger whether bandwidth was a problem, because I assumed that many areas of Brazil would be poorly provisioned with network connections. She said that the organizers heard only a few complaints, and that bandwidth was not an issue. This is a tribute, I think, to the brilliant engineering that developers have put into designing and implementing streaming protocols.

◉ Many parallel activities were offered on virtual streams that the organizers called "rooms." Thus, there would be a room for each track, where people could stay for multiple sessions.

Tracks, I should explain, form the basic structure of TDC. Typical tracks in 2020 included Agile, Agile for business, Artificial Intelligence and data, programming language, etc.—the kinds of topics that are popular at all computer conferences today. Attendees pay separately for each track they want to attend.

Some sponsors also rented "rooms" to offer demos and other content. Registration and questions were also handled in a dedicated room.

◉ If participants wanted to connect with a speaker after a talk, they could leave the track's room and visit a separate room for informal discussion. These went very well, showing that some 200 people could interact in an orderly fashion online. Some of the sessions went on until 11:00 at night, with perhaps 20 stalwart attendees lasting the whole time.

Senger said that interactions in the rooms were probably more formal than face-to-face meetings, which is a drawback of virtual meetings. But they allowed many more people to participate for a longer time than when sessions are on-site.

◉ Participants could network with each other in a serendipitous way, a little like hallway chats at face-to-face conferences. At TDCOnline, you could enter a room with another randomly chosen participant and introduce yourselves to each other for three minutes.

◉ Participants could transition between rooms with a single click. This is one of the advantages of the software used by TDC to administer the conference, Hopin. Hopin was available at a reasonable price and offered important features TDC needed. It let them set up separate tracks (one per room, as said before) and set participants' permissions so they had access only to the tracks they paid for.

◉ Session monitors followed the presentations in real-time and put resources up quickly in chat boxes. When a speaker mentioned a resource such as room to move it, the monitor could post a link to the resource within a couple seconds. They were so effective that some participants assumed that an NLP-powered chatbot was doing it.

◉ Each track during the on-site conference used to continue for eight hours, and people were encouraged to stay for the whole day. (They were always charged for the entire track.) Organizers realized that eight hours of conferencing online would grueling--even if some participants were delighted to stay till 11:00 at night--so tracks were reduced to four hours.

◉ Along with the reduction in the length of a track, sessions were reduced to 25 minutes each. This shifted much of the discussion from the formal session to the informal follow-up. And this, in turn, allowed the discussion to reflect better the interests of the attendees.

◉ There were also more panels than in previous years. The debates there were lively and productive, according to Senger. Some panels went on for three hours. Attendees could submit questions and vote on the questions submitted by others, so the most popular questions got plenty of attention.

What was the payoff for all this insight and planning? The conference ultimately drew a respectable number of 6,750 attendees, who logged in from every region of Brazil—bringing much broader participation geographically than ever before—and included people from 21 other countries too. (These countries are marked by red dots in the article image) Remember that the sessions were all in Portuguese, so this reveals a thriving international community of Brazilians and other people fluent in Portuguese. About 15 sponsors participated. A sparkling, fast-paced video conveys some of the experience.

I asked whether different types of people came this year, because it was online. Except for the great geographic spread, Senger said people seemed to be basically like the ones who came to earlier TDCs. The only difference is a slight decrease in experience levels. Only 39% of attendees had ten or more years of experience in their fields, compared to an average of 44% before. But there was a big increase among the great with 6-10 years of experience. This is understandable, because the conference was four times as large this year. There are a lot more people with 6-10 years of experience than with ten years.

As you can probably tell from my description of the conference, it depended heavily on the responsiveness and expertise of the staff. I asked Senger how they could handle 6,750 with only 30 staff, and she answered that the staff are well-trained and have been running their conferences for years. The speakers need a great deal of support, starting by testing their connections two weeks before the conference, ensuring they were ready the day before, and setting up their session right before it started.

I also asked how easily attendees picked up the rules for attendance. Senger said that it required a lot of explanation. The organizers are preparing a video that attendees can view before future conferences to grasp what they can do to make their participation as effective as possible.

TCDOnline was successful because of the unique structure and tools provided to speakers, sponsors, and attendees. The organizers are now consulting with other organizations to teach the lessons of the first TCDOnline and help others produce engaging and educational conferences during this period of physical distancing—and perhaps even after that period has ended.

Source: lpi.org

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How to use the Linux 'lsof' command to list open files

Linux “open files” FAQ: Can you share some examples of how to show open files on a Linux system (i.e., how to use the lsof command)?

lsof command background

The Linux lsof command lists information about files that are open by processes running on the system. The lsof command itself stands for “list of open files.” In this article I’ll share some lsof command examples.

Also Read: 102-500: Linux Administrator - 102 (LPIC-1 102)

I assume you’re logged in as root

One other note: In these examples I'll assume that you're logged in as the Unix/Linux root user. If not, you’re lsof command output may be significantly limited. If you’re logged in as a non-root user, either su to root, or use sudo to run these commands.

Basic Linux lsof command examples

Typing the lsof command by itself lists all open files belonging to all active processes on the system:

$ lsof

On my current Mac OS X system, which has been running for a long time, this shows a lot of open files, 1,582 to be specific:

$ lsof | wc -l
    1582

Note that I didn’t have to be logged in as the root user to see this information on my Mac system.

Adding the head command to lsof shows what some of this output looks like:

$ lsof | head

COMMAND     PID USER   FD     TYPE     DEVICE  SIZE/OFF      NODE NAME
loginwind    32   Al  cwd      DIR       14,2      1564         2 /
loginwind    32   Al  txt      REG       14,2   1754096 243026930 /System/Library/CoreServices/loginwindow.app/Contents/MacOS/loginwindow
loginwind    32   Al  txt      REG       14,2    113744   3190067 /System/Library/LoginPlugins/FSDisconnect.loginPlugin/Contents/MacOS/FSDisconnect
loginwind    32   Al  txt      REG       14,2    425504 117920371 /System/Library/LoginPlugins/DisplayServices.loginPlugin/Contents/MacOS/DisplayServices
loginwind    32   Al  txt      REG       14,2      3144   3161654 /System/Library/ColorSync/Profiles/sRGB Profile.icc
loginwind    32   Al  txt      REG       14,2     96704 242998403 /System/Library/PrivateFrameworks/MachineSettings.framework/Versions/A/MachineSettings
loginwind    32   Al  txt      REG       14,2     51288 251253153 /private/var/folders/h5/h59HESVvEmG+3I4Q8lOAxE+++TI/-Caches-/mds/mdsDirectory.db
loginwind    32   Al  txt      REG       14,2    724688 117923285 /System/Library/LoginPlugins/BezelServices.loginPlugin/Contents/MacOS/BezelServices
loginwind    32   Al  txt      REG       14,2    329376 117923166 /System/Library/Extensions/IOHIDFamily.kext/Contents/PlugIns/IOHIDLib.plugin/Contents/MacOS/IOHIDLib

Common lsof options

As mentioned, these details go on for 1,582 lines, so it helps to have some way to weed through that output, whether that involves using the grep command, or some of the lsof options shown below.

This command lists all open files belonging to PID (process ID) 11925:

$ lsof -p 11925

This command lists all open files belonging to processes owned by the user named "al":

$ lsof -u al

This command lists files that are open in the directory specified, but it does not descend into sub-directories:

$ lsof +d '/Users/al'

The next command lists files that are open in the directory specified, and also descends into sub-directories. Beware: this can take a very long time to run for large directory structures:

$ lsof +D '/Users/al'

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Sed Command in Unix and Linux Examples

Sed is a Stream Editor used for modifying the files in unix (or linux). Whenever you want to make changes to the file automatically, sed comes in handy to do this. Most people never learn its power; they just simply use sed to replace text. You can do many things apart from replacing text with sed. Here I will describe the features of sed with examples.

Consider the below text file as an input.

>cat file.txt
unix is great os. unix is opensource. unix is free os.
learn operating system.
unixlinux which one you choose.

Sed Command Examples

1. Replacing or substituting string

Sed command is mostly used to replace the text in a file. The below simple sed command replaces the word "unix" with "linux" in the file.

>sed 's/unix/linux/' file.txt
linux is great os. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you choose.

Here the "s" specifies the substitution operation. The "/" are delimiters. The "unix" is the search pattern and the "linux" is the replacement string.

By default, the sed command replaces the first occurrence of the pattern in each line and it won't replace the second, third...occurrence in the line.

2. Replacing the nth occurrence of a pattern in a line.

Use the /1, /2 etc flags to replace the first, second occurrence of a pattern in a line. The below command replaces the second occurrence of the word "unix" with "linux" in a line.

>sed 's/unix/linux/2' file.txt
unix is great os. linux is opensource. unix is free os.
learn operating system.
unixlinux which one you choose.

3. Replacing all the occurrence of the pattern in a line.

The substitute flag /g (global replacement) specifies the sed command to replace all the occurrences of the string in the line.

>sed 's/unix/linux/g' file.txt
linux is great os. linux is opensource. linux is free os.
learn operating system.
linuxlinux which one you choose.

4. Replacing from nth occurrence to all occurrences in a line.

Use the combination of /1, /2 etc and /g to replace all the patterns from the nth occurrence of a pattern in a line. The following sed command replaces the third, fourth, fifth... "unix" word with "linux" word in a line.

>sed 's/unix/linux/3g' file.txt
unix is great os. unix is opensource. linux is free os.
learn operating system.
unixlinux which one you choose.

5. Changing the slash (/) delimiter

You can use any delimiter other than the slash. As an example if you want to change the web url to another url as

>sed 's/http:\/\//www/' file.txt

In this case the url consists the delimiter character which we used. In that case you have to escape the slash with backslash character, otherwise the substitution won't work.

Using too many backslashes makes the sed command look awkward. In this case we can change the delimiter to another character as shown in the below example.

>sed 's_http://_www_' file.txt
>sed 's|http://|www|' file.txt

6. Using & as the matched string

There might be cases where you want to search for the pattern and replace that pattern by adding some extra characters to it. In such cases & comes in handy. The & represents the matched string.

>sed 's/unix/{&}/' file.txt
{unix} is great os. unix is opensource. unix is free os.
learn operating system.
{unix}linux which one you choose.

>sed 's/unix/{&&}/' file.txt
{unixunix} is great os. unix is opensource. unix is free os.
learn operating system.
{unixunix}linux which one you choose.

7. Using \1,\2 and so on to \9

The first pair of parenthesis specified in the pattern represents the \1, the second represents the \2 and so on. The \1,\2 can be used in the replacement string to make changes to the source string. As an example, if you want to replace the word "unix" in a line with twice as the word like "unixunix" use the sed command as below.

>sed 's/\(unix\)/\1\1/' file.txt
unixunix is great os. unix is opensource. unix is free os.
learn operating system.
unixunixlinux which one you choose.

The parenthesis needs to be escaped with the backslash character. Another example is if you want to switch the words "unixlinux" as "linuxunix", the sed command is

>sed 's/\(unix\)\(linux\)/\2\1/' file.txt
unix is great os. unix is opensource. unix is free os.
learn operating system.
linuxunix which one you choose.

Another example is switching the first three characters in a line

>sed 's/^\(.\)\(.\)\(.\)/\3\2\1/' file.txt
inux is great os. unix is opensource. unix is free os.
aelrn operating system.
inuxlinux which one you choose.

8. Duplicating the replaced line with /p flag

The /p print flag prints the replaced line twice on the terminal. If a line does not have the search pattern and is not replaced, then the /p prints that line only once.

>sed 's/unix/linux/p' file.txt
linux is great os. unix is opensource. unix is free os.
linux is great os. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you choose.
linuxlinux which one you choose.

9. Printing only the replaced lines

Use the -n option along with the /p print flag to display only the replaced lines. Here the -n option suppresses the duplicate rows generated by the /p flag and prints the replaced lines only one time.

>sed -n 's/unix/linux/p' file.txt
linux is great os. unix is opensource. unix is free os.
linuxlinux which one you choose.

If you use -n alone without /p, then the sed does not print anything.

10. Running multiple sed commands.

You can run multiple sed commands by piping the output of one sed command as input to another sed command.

>sed 's/unix/linux/' file.txt| sed 's/os/system/'
linux is great system. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you chosysteme.

Sed provides -e option to run multiple sed commands in a single sed command. The above output can be achieved in a single sed command as shown below.

>sed -e 's/unix/linux/' -e 's/os/system/' file.txt
linux is great system. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you chosysteme.

11. Replacing string on a specific line number.

You can restrict the sed command to replace the string on a specific line number. An example is

>sed '3 s/unix/linux/' file.txt
unix is great os. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you choose.

The above sed command replaces the string only on the third line.

12. Replacing string on a range of lines.

You can specify a range of line numbers to the sed command for replacing a string.

>sed '1,3 s/unix/linux/' file.txt
linux is great os. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you choose.

Here the sed command replaces the lines with range from 1 to 3. Another example is

>sed '2,$ s/unix/linux/' file.txt
linux is great os. unix is opensource. unix is free os.
learn operating system.
linuxlinux which one you choose.

Here $ indicates the last line in the file. So the sed command replaces the text from second line to last line in the file.

13. Replace on a lines which matches a pattern.

You can specify a pattern to the sed command to match in a line. If the pattern match occurs, then only the sed command looks for the string to be replaced and if it finds, then the sed command replaces the string.

>sed '/linux/ s/unix/centos/' file.txt
unix is great os. unix is opensource. unix is free os.
learn operating system.
centoslinux which one you choose.

Here the sed command first looks for the lines which has the pattern "linux" and then replaces the word "unix" with "centos".

14. Deleting lines.

You can delete the lines a file by specifying the line number or a range or numbers.

>sed '2 d' file.txt
>sed '5,$ d' file.txt

15. Duplicating lines

You can make the sed command to print each line of a file two times.

>sed 'p' file.txt

16. Sed as grep command

You can make sed command to work as similar to grep command.

>grep 'unix' file.txt
>sed -n '/unix/ p' file.txt

Here the sed command looks for the pattern "unix" in each line of a file and prints those lines that has the pattern.

You can also make the sed command to work as grep -v, just by using the reversing the sed with NOT (!).

>grep -v 'unix' file.txt
>sed -n '/unix/ !p' file.txt

The ! here inverts the pattern match.

17. Add a line after a match.

The sed command can add a new line after a pattern match is found. The "a" command to sed tells it to add a new line after a match is found.

>sed '/unix/ a "Add a new line"' file.txt
unix is great os. unix is opensource. unix is free os.
"Add a new line"
learn operating system.
unixlinux which one you choose.
"Add a new line"

18. Add a line before a match

The sed command can add a new line before a pattern match is found. The "i" command to sed tells it to add a new line before a match is found.

>sed '/unix/ i "Add a new line"' file.txt
"Add a new line"
unix is great os. unix is opensource. unix is free os.
learn operating system.
"Add a new line"
unixlinux which one you choose.

19. Change a line

The sed command can be used to replace an entire line with a new line. The "c" command to sed tells it to change the line.

>sed '/unix/ c "Change line"' file.txt
"Change line"
learn operating system.
"Change line"

20. Transform like tr command

The sed command can be used to convert the lower case letters to upper case letters by using the transform "y" option.

>sed 'y/ul/UL/' file.txt
Unix is great os. Unix is opensoUrce. Unix is free os.
Learn operating system.
UnixLinUx which one yoU choose.

Here the sed command transforms the alphabets "ul" into their uppercase format "UL"

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Linux gzip: How to work with compressed files

If you work much with Unix and Linux systems you'll eventually run into the terrific file compression utilities, gzip and gunzip. As their names imply, the first command creates compressed files (by gzip'ing them), and the second command unzip's those files.

In this post I take a quick look at the gzip and gunzip file compression utilities, along with their companion tools you may not have known about: zcat, zgrep, and zmore.

The Unix/Linux gzip command

You can compress a file with the Unix/Linux gzip command. For instance, if I run an ls -l command on an uncompressed Apache access log file named access.log, I get this output:

-rw-r--r--   1 al  al  22733255 Aug 12  2008 access.log

Note that the size of this file is 22,733,255 bytes. Now, if we compress the file using gzip, like this:

gzip access.log

we end up creating a new, compressed file named access.log.gz. Here's what that file looks like:

-rw-r--r--   1 al  al  2009249 Aug 12  2008 access.log.gz

Notice that the file has been compressed from 22,733,255 bytes down to just 2,009,249 bytes. That's a huge savings in file size, roughly 10 to 1(!).

There's one important thing to note about gzip: The old file, access.log, has been replaced by this new compressed file, access.log.gz. This might freak you out a little the first time you use this command, but very quickly you get used to it. (If for some reason you don't trust gzip when you first try it, feel free to make a backup copy of your original file.)

The Linux gunzip command

The gunzip ("g unzip") command works just the opposite of gzip, converting a gzip'd file back to its original format. In the following example I'll convert the gzip'd file we just created back to its original format:

gunzip access.log.gz

Running that command restores our original file, as you can see in this output:

-rw-r--r--   1 al  al  22733255 Aug 12  2008 access.log

The Linux file compress utilities (zcat, zmore, zgrep)

I used to think I had to uncompress a gzip'd file to work on it with commands like cat, grep, and more, but at some point I learned there were equivalent gzip versions of these same commands, appropriately named zcat, zgrep, and zmore. So, anything you would normally do on a text file with the first three commands you can do on a gzip'd file with the last three commands.

For instance, instead of using cat to display the entire contents of the file, you use zcat to work on the gzip'd file instead, like this:

zcat access.log.gz

(Of course that output will go on for a long time with roughly 22MB of compressed text.)

You can also scroll through the file one page at a time with zmore:

zmore access.log.gz

And finally, you can grep through the compressed file with zgrep:

zgrep '/java/index.html' access.log.gz

There are also two other commands, zcmp and zdiff, that let you compare compressed files, but I personally haven't had the need for them. However, as you can imagine, they work like this:

zmp file1.gz file2.gz

or

zdiff file1.gz file2.gz

Linux gzip / compress summary

As a quick summary, just remember that you don't have to uncompress files to work on them, you can use the following z-utilities to work on the compressed files instead:

◉ zcat
◉ zmore
◉ zgrep
◉ zcmp
◉ zdiff

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The Linux 'rm' command (remove files and directories)

Linux FAQ: How do I delete files (remove files) on a Unix or Linux system?

The Linux rm command is used to remove files and directories. (As its name implies, this is a dangerous command, so be careful.)

Let's take a look at some rm command examples, starting from easy examples to more complicated examples.

How to delete files with rm

In its most basic use, the rm command can be used to remove one file, like this:

rm oldfile.txt

You can also use the rm command to delete multiple Linux files at one time, like this:

rm file1 file2 file3

If you prefer to be careful when deleting files, use the -i option with the rm command. The -i stands for "inquire", so when you use this option the rm command prompts you with a yes/no prompt before actually deleting your files:

rm -i files file2 file3

How to delete directories with rm

To delete Linux directories with the rm command, you have to specify the -r option, like this:

rm -r OldDirectory

The -r option means "recursive", and therefore this command recursively deletes all files and directories in the directory named OldDirectory.

As a warning, this command is obviously very dangerous, so be careful. Some people always add the inquire option when deleting directories, like this:

rm -ir OldDirectory

You can also delete multiple directories at one time, like this:

rm -r Directory1 Directory2 Directory3

How to use wildcards with rm

Unix and Linux systems have always supported wildcard characters, so in this case you can delete files and directories even faster. For instance, to delete all HTML files in the current directory, use this command:

rm *.html

Note that unlike DOS, you don't actually need the "." before the "html" in that command, so you can shorten the command like this:

rm *html

Unix and Linux wildcard characters and commands don't care at all about "." characters and filename extensions, so the "." is not needed.

You can also use wildcard characters in the middle of a filename or at the end of the filename. Here's an example where I'm deleting all files in the current directory that begin with the string "index":

rm index*

This command deletes files named index.html, index.php, and in general, any filename that begins with the character string "index".

You can also use wildcard characters like this to delete multiple files or directories:

rm Chapter[123].txt

That command deletes the files Chapter1.txt, Chapter2.txt, and Chapter3.txt, all in one command.

More Linux rm commands

There are probably many more Linux delete commands you can issue with the rm command. For instance, you can delete files and directories that aren't in the current directory. Here's an example where I delete a file named foo.txt that's in the /tmp directory:

rm /tmp/foo.txt

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