Questions tagged [command-line]

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

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291
votes
16answers
350k 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, 25 in this case? Also, what's the easiest way to do it just using bash for floating point? For ...
341
votes
10answers
138k 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 ...
206
votes
8answers
158k 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 ...
263
votes
6answers
26k 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 ...
450
votes
4answers
158k 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 -- in there?
119
votes
36answers
56k views

Quick directory navigation in the bash shell

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 /[full-path]/...
81
votes
4answers
261k views

Why do we use “./” to execute a file?

Why do we use ./filename to execute a file in linux? Why not just enter it like other commands gcc, ls etc...
306
votes
11answers
384k views

How can I run a command which will survive terminal close?

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 such ...
27
votes
3answers
5k views

Order of redirections

I don't quite understand how the computer reads this command. cat file1 file2 1> file.txt 2>&1 If I understand, 2>&1 simply redirect Standard Error to Standard Output. By that ...
79
votes
11answers
22k 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?
400
votes
9answers
161k views

When should I not kill -9 a process?

I am always very hesitant to run kill -9, but I see other admins do it almost routinely. I figure there is probably a sensible middle ground, so: When and why should kill -9 be used? When and why ...
146
votes
10answers
58k 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.
96
votes
5answers
113k views

What is the difference between Halt and Shutdown commands?

What is the difference between the halt and shutdown commands?
20
votes
3answers
3k views

Manipulating X key and pointer grabs on the command line

What command line tools exist to list and manage X server grabs? (That's grab as in key and pointer grabs, i.e. restricting the use of a particular key or mouse button to a particular application, or ...
46
votes
19answers
24k views

Is there a robust command line tool for processing csv files?

I work with CSV files and sometimes need to quickly check the contents of a row or column from the command line. In many cases cut, head, tail, and friends will do the job; however, cut cannot easily ...
94
votes
63answers
46k views

What are your favorite command line features or tricks?

Share your command line features and tricks for Unix/Linux. Try to keep it shell/distro agnostic if possible. Interested in seeing aliases, one-liners, keyboard shortcuts, small shell scripts, etc.
178
votes
8answers
128k 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 ...
156
votes
16answers
231k 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 ...
524
votes
37answers
549k 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 ...
260
votes
19answers
180k 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 setup ...
109
votes
6answers
331k views

Pass the output of previous command to next as an argument

I've a command that outputs data to stdout (command1 -p=aaa -v=bbb -i=4). The output line can have the following value: rate (10%) - name: value - 10Kbps I want to grep that output in order to store ...
23
votes
4answers
111k views

Storing output of command in shell variable [duplicate]

I have an operation using cut that I would like to assign result to a variable var4=echo ztemp.xml |cut -f1 -d '.' I get the error: ztemp.xml is not a command The value of var4 never gets ...
194
votes
18answers
183k 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 /...
143
votes
8answers
511k views

Run a command without making me wait

On the CLI, sometimes a command I type takes a while to complete, and sometimes I know when that's about to happen. I'm a bit confused on "backgrounding" and such in Linux. What is the most common (...
110
votes
6answers
111k 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 ...
76
votes
15answers
65k 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 ...
26
votes
4answers
2k views

What is this shell/Bash syntax: someVariable=someValue someCommand [duplicate]

One of my coworkers has provided me with a Bash syntax that I am unfamiliar with. My Google foo has failed me on figuring out what it does and why/when I should use it. The command that he sent me ...
96
votes
10answers
6k 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 ...
24
votes
5answers
62k views

How to use /dev/fb0 as a console from userspace, or output text to it

So I have a Palm Pre (original P100EWW) model that I enabled developer mode on, and installed a Debian Squeeze chroot. Works great. I have plans to use this for ANYTHING (bittorrent peer, web server)...
49
votes
6answers
22k views

Single dashes `-` for single-character options, but double dashes `--` for words?

Where did the convention of using single dashes for letters and doubles dashes for words come from and why is continued to be used? For example if I type in ls --help, you see: -a, --all ...
11
votes
5answers
4k views

What's the best way to take a segment out of a text file?

What's a good way of extracting say, lines 20 -45 out of a huge text file. Non-interactively of course!
60
votes
7answers
21k views

how to glob every hidden file except current and parent directory [duplicate]

I want to glob every hidden file and directory, but not the current (.) and parent directory (..). I am using bash. Observe current behaviour: $ ls -a . .. ...a ...aa ..a ..aa .a .aa .aaa ...
22
votes
3answers
23k views

How do you send command line apps directly to the background?

I already know that pressing ctrl+z stops the app, then I can send the app to background with the bg command, but that means there is a brief preiod of time that the app is stopped. How do I send the ...
12
votes
2answers
3k views

grep - why do brackets in grep pattern remove the grep process from ps results?

Why do brackets in a grep pattern remove the grep process from ps results? $ ps -ef | grep XXXX [...] XXXX [...] grep XXXX $ ps -ef | grep [X]XXX [...] XXXX
32
votes
6answers
53k views

find n most frequent words in a file

I want to find, say, 10 most common word in a text file. Firstly, solution should be optimized for keystrokes (in other words - my time). Secondly, for the performance. Here is what I have so far to ...
34
votes
6answers
11k views

Why is echo a shell built in command?

$ which echo echo: shell built-in command. $ which ls /bin/ls $ which cat /bin/cat Why is echo not an independent utility like ls, ps, cat etc? Why is it shell specific? Any good reasons?
472
votes
25answers
480k views

Repeat a Unix command every x seconds forever

There's a built-in 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 ...
116
votes
12answers
126k 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.
115
votes
13answers
97k 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, )...
99
votes
5answers
233k views

Usage of dash (-) in place of a filename

For a command, if using - as an argument in place of a file name will mean STDIN or STDOUT. But in this example, it creates a file with the name -: echo hello > - How can I make - in this ...
103
votes
5answers
120k views

Understanding the exclamation mark (!) in bash

I used history | less to get the lines of previous commands and from the numbers on the left hand side I found the line I wanted repeated (eg. 22) and did !22 at the command prompt and it worked -...
69
votes
9answers
180k views

How to insert text before the first line of a file?

I've been looking around sed command to add text into a file in a specific line. This works adding text after line 1: sed '1 a\ But I want to add it before line 1. It would be: sed '0 a\ but I get ...
19
votes
5answers
31k views

Output the common lines (similarities) of two text files (the opposite of diff)?

Diff is a great tool to display the changes between two files. But how to display the similarities of two text files (while ignoring the differences)? I.e. sample input: a: Foo Bar X Hello World 42 ...
8
votes
4answers
2k views

How to print the name of missing files in a folder?

I have 2000+ files in a folder, but there are few files missing from the folder. Name of the files are like GLDAS_NOAH025SUBP_3H.A2003001.0000.001.2015210044609.pss.grb GLDAS_NOAH025SUBP_3H....
7
votes
1answer
660 views

du results on filesystem inconsistent with df

What explains the discrepancy in usage (82 GB vs 13 GB) that I see below? Using df: $ df -h / Filesystem Size Used Avail Use% Mounted on /dev/sda2 96G 82G 9.9G 90% / ...
44
votes
6answers
14k 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
56
votes
11answers
99k views

Is there a simple linux command that will tell me what my display manager is?

Is there a simple linux command that will tell me what my display manager is? I'm using Xfce. Are different desktop environments usually affiliated with different display managers?
16
votes
3answers
7k views

Find filesystem of an unmounted partition from a script

I'm writing a custom automated install using AIF (Arch Installation Framework), and I need to find the filesystem on a partition given a partition. So far I have this: grok_partitions () { local ...
11
votes
1answer
5k views

How to run my own program without specifying its path

Let's suppose I have compiled something and I run it like so: $ /path/to/my/executable/mycmd Hello World What do I need to do to run it like $ mycmd Hello World from everywhere in my computer?
11
votes
4answers
822 views

ls command operating differently depending on recipient

How does commands like ls know what its stdout is? It seems ls is operating different depending on what the target stdout is. For example if I do: ls /home/matt/tmp the result is: a.txt b.txt c....