The command-line is the interactive interface to your shell.

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167
votes
23answers
99k views

Repeat a Unix command every x seconds forever

There's a builtin Unix command repeat whose first argument is the number of times to repeat a command, where the command (with any arguments) is specified by the remaining arguments to repeat. For ...
163
votes
5answers
10k views

What's the difference between $(stuff) and `stuff`?

There are two syntaxes for command substitution: with dollar-parentheses and with backticks. Running top -p $(pidof init) and top -p `pidof init` gives the same output. Are these two ways of doing the ...
120
votes
5answers
22k views

I deleted /bin/rm. How do I recover it?

Just for fun, I thought I would use this command on my Raspberry PI running Raspbian: sudo rm -f /bin/rm I thought I could just reinstall coreutils: I was wrong! apt-get install --reinstall ...
113
votes
15answers
58k views

How to do integer & float calculations, in bash or other languages/frameworks?

Using echo "20+5" literally produces the text "20+5" What command can I use to get the numeric sum, e.g. 25 in this case. Also, what's the easiest way to do it just using bash for floating point, ...
110
votes
28answers
36k views

Tracking down where disk space has gone on Linux?

When administering Linux systems I often find myself struggling to track down the culprit after a partition goes full. I normally use du / | sort -nr but on a large filesystem this takes a long time ...
96
votes
13answers
39k views

How to have tail -f show colored output

I'd like to be able to tail the output of a server log file that has messages like: INFO SEVERE etc, and if it's SEVERE, show the line in red; if it's INFO, in green. What kind of alias can I ...
84
votes
6answers
41k views

Keep SSH Sessions running after disconnection

I sometimes have long running processes that I want to kick off before going home, so I create a SSH session to the server to start the process, but then I want to close my laptop and go home and ...
79
votes
6answers
49k views

How can I close a terminal without killing the command running in it?

Sometimes I want to start a process and forget about it. If I start it from the command line, like this: redshift I can't close the terminal, or it will kill the process. Can I run a command in ...
76
votes
2answers
20k views

What does “--” (double-dash) mean? (also known as “bare double dash”)

I have seen -- used in the compgen command. For example: compgen -W "foo bar baz" -- b What is the meaning of the --.
65
votes
7answers
24k views

How can I find broken symlinks

Is there a way to find all symbolic links that don't point anywere? find ./ -type l will give me all symbolic links, but makes no distinction between links that go somewhere and links that don't. ...
62
votes
25answers
10k views

Quick directory navigation in the terminal

I would like to frequently switch between directories that are in totally unrelated paths, for example /Project/Warnest/docs/ and ~/Dropbox/Projects/ds/test/. But I don't want to type cd ...
58
votes
10answers
18k views

How to grep a specific line _and_ the first line of a file?

Assuming a simple grep such as: $ psa aux | grep someApp 1000 11634 51.2 0.1 32824 9112 pts/1 SN+ 13:24 7:49 someApp This provides much information, but as the first line of the ps ...
58
votes
9answers
2k views

Remember a half-typed command while I check something

I often find myself in the following position: I've started typing a long command at the bash prompt, but half-way through I find out I need to check something with another command. This is a problem ...
51
votes
6answers
6k views

When is xargs needed?

The xargs command always confuses me. Is there a general rule that can help me figure out when I need it? Consider the two examples below: $ \ls | grep Cases | less prints the files that match ...
50
votes
8answers
12k views

How do I delete a file whose name begins with “-” (hyphen a.k.a. dash or minus)?

How do you remove a file whose filename begins with a dash (hyphen or minus) -? I'm ssh'd into a remote OSX server and I have this file in my directory: tohru:~ $ ls -l total 8 -rw-r--r-- 1 me ...
47
votes
11answers
22k views

how do you sort du output by size?

How do you sort du -sh /dir/* by size? I read one site that said use | sort -n but that's obviously not right. Here's an example that is wrong. [~]# du -sh /var/* | sort -n 0 /var/mail 1.2M ...
46
votes
3answers
2k views

Why is `--human-readable` needed and not default?

Several command line tools use the -h or --human-readable option to print file size in a human readable format (i.e., 36G vs 37550836). Why is this option needed and not the default? Aren't these ...
46
votes
6answers
19k views

How can I move files and view the progress (e.g. with a progress bar)?

When moving large directories using mv, is there a way to view the progress (%)? The cp command on gentoo had a -g switch that showed the progress.
44
votes
3answers
34k views

How to tell gzip to keep original file?

I would like to compress a text file using gzip command line tool while keeping the original file. By default running the following command gzip file.txt results in modifying this file and renaming ...
44
votes
5answers
2k views

cd by just typing the directory's name?

I either had this somewhere 20 years ago or I dreamed about it. Basically: If if type blobblob I get blobblob: command not found Fair enough. I would like it so that when my shell gets those ...
39
votes
8answers
27k views

How can I edit multiple files in VIM?

I know I can open multiple files with vim by doing something like vim 2011-12*.log, but how can I switch between files and close the files one at a time? Also, how can I tell the file name of the ...
38
votes
3answers
50k views

ssh-add complains: Could not open a connection to your authentication agent

I've been trying to get ssh-add working on a RaspberryPi running Raspbian. I can start ssh-agent, when I do it gives the following output into the terminal: ...
37
votes
5answers
20k views

How can I send stdout to multiple commands?

There are some commands which filter or act on input, and then pass it along as output, I think usually to stdout - but some commands will just take the stdin and do whatever they do with it, and ...
35
votes
6answers
20k views

Is there a tool to get the lines in one file that are not in another?

Is there any tool that can get lines which file A contains, but file B doesn't? I could make a little simple script with, e.g, perl, but if something like that already exists, I'll save my time from ...
35
votes
6answers
67k views

How to overwrite target files with mv?

I have a ton of files and dirs in a subdirectory I want to move to the parent directory. There are already some files and dirs in the target directory which need to be overwritten. Files that are only ...
35
votes
3answers
16k views

What is the difference between Halt and Shutdown commands?

What is the difference between the halt and shutdown commands?
34
votes
8answers
6k views

Easy way to determine virtualization technology

I have command line access to a Linux machine which may or may not be virtualized. I want to determine what kind of virtualization technology it runs on, if any (VMWare, VirtualBox, KVM, OpenVZ, Xen, ...
32
votes
4answers
2k views

Reverse grepping

Let's say, I have a really big text file (about 10.000.000 lines). I need to grep it from the end and save result to a file. What's the most efficient way to accomplish task?
32
votes
10answers
13k views

How do I reuse the last output from the command line?

This is a noob question, but I'd like to know how to reuse the last output from the console, ie: pv-3:method Xavier$ python -c "from distutils.sysconfig import get_python_lib; print get_python_lib()" ...
31
votes
9answers
69k views

How do I make my pc speaker beep

Using bash, how can I make the pc speaker beep? Something like echo 'beepsound' > /dev/pcspkr would be nice.
31
votes
7answers
6k views

Linux tools to treat files as sets and perform set operations on them

Does anyone know of any linux tool specifically designed to treat files as sets and perform set operations on them? Like difference, intersection, etc?
29
votes
4answers
2k views

Is there a one-liner that allows me to create a directory and move into it at the same time?

I find myself repeating a lot of: mkdir longtitleproject cd longtitleproject Is there a way of doing it in one line without repeating the directory name? I'm on bash here.
29
votes
3answers
35k views
29
votes
8answers
18k views

Markdown Viewer

I found a file formatted with Markdown. Could you guys suggest what viewer that I could use to view this type of files? Hopefully one without gui (if it's possible) Update I was actually looking for ...
28
votes
7answers
168k views

How do I zip/unzip on the unix command line?

How can I create and extract zip archives from the command line?
27
votes
5answers
6k views

How to echo a bang!

I tried to create a script by echo'ing the contents into a file, instead of opening it with a editor echo -e "#!/bin/bash \n /usr/bin/command args" > .scripts/command The output: bash: ...
27
votes
4answers
17k views

How to redirect output of wget as input to unzip?

I have to download a file from this link. The file download is a zip file which I will have to unzip in the current folder. Normally, I would download it first, then run the unzip command. $ wget ...
26
votes
3answers
2k views

Why shouldn't someone use passwords in the command line?

Why do people fear writing passwords in the command line? The history file is located in ~/.history, so it's available only to the user who executed the commands (and root).
26
votes
5answers
3k views

How do I get a websites title using command line?

I want a command line program that prints the title of a website. For e.g.: Alan:~ titlefetcher http://www.youtube.com/watch?v=Dd7dQh8u4Hc should give: Why Are Bad Words Bad? You give it the ...
26
votes
6answers
31k views

Where do files go when the rm command is issued?

Recently I accidentally did rm on a set of files and it got me thinking where exactly these files end up? That is to say, when working with a GUI, deleted files go to the Trash. What's the equivalent ...
25
votes
12answers
35k views

Efficiently delete large directory containing thousands of files

We have an issue with a folder becoming unwieldy with hundreds of thousands of tiny files. There are so many files that performing rm -rf returns an error and instead what we need to do is something ...
25
votes
3answers
30k views

Set volume from terminal

Is it possible to set the audio volume using the terminal?, instead of clicking the speaker icon in the topbar, the reason I want need to do this is because my keyboard does not have a volume ...
25
votes
3answers
9k views

How can I “relink” a lot of broken symlinks?

I have a directory tree which has a bunch of symbolic links to files under /home... however, I have moved /home to /mnt/home and need a way to "relink" all of the symlinks. Does such functionality ...
25
votes
4answers
18k views

What is the mknod command used for?

I just started using Ubuntu as my main OS and I wanted to learn about things I should not do, and learn by the bad things people have done in the past. I came across these email about horror stories ...
24
votes
4answers
2k views

Is it possible to define a command in bash?

For example, can I set gb = cd /media/Dan/evolution So that everytime I execute gb in bash, I can cd to that particular directory? I find something online, alias command. But It seems can't do the ...
24
votes
9answers
9k views

How to understand what's taking up space?

I'm looking for a linux alternative to WinDirStat. I would like to know what is taking up space on my hard drives. A program that works on console and doesn't require a UI is preferred .
24
votes
8answers
2k views

Dealing with file names with special first characters (ex. ♫)

I have recently come across a file whose name begins with the character '♫'. I wanted to copy this file, feed it into ffmpeg, and reference it in various other ways in the terminal. I usually ...
24
votes
5answers
15k views

Split pages in pdf

I have a scanned pdf file which has scanned two pages on one virtual page (page in pdf file). The resolution is with good quality. The problem is I have to zoom when reading and drag from left to the ...
24
votes
10answers
14k views

Which mp3 tagging tool for Linux?

Which app would you recommend for Linux to tag MP3s? Under Windows I used to use tag&rename and liked it a lot; it works well under Wine, but I want something that runs natively
24
votes
5answers
5k views

How do I send stdin to the clipboard?

Is there functionality in unix that allows for the following: echo "Some Text" | copy-to-clipboard