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1500 questions
666
votes
11 answers

Why is it better to use "#!/usr/bin/env NAME" instead of "#!/path/to/NAME" as my shebang?

I notice that some scripts which I have acquired from others have the shebang #!/path/to/NAME while others (using the same tool, NAME) have the shebang #!/usr/bin/env NAME. Both seem to work properly. In tutorials (on Python, for example), there…
TheGeeko61
  • 7,041
655
votes
4 answers

Using "${a:-b}" for variable assignment in scripts

I have been looking at a few scripts other people wrote (specifically Red Hat), and a lot of their variables are assigned using the following notation VARIABLE1="${VARIABLE1:-some_val}" or some expand other variables VARIABLE2="${VARIABLE2:-`echo…
Justin Garrison
  • 7,459
648
votes
24 answers

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 example, % repeat 100 echo "I will not automate…
dreeves
  • 6,629
644
votes
11 answers

How to append multiple lines to a file

I am writing a bash script to look for a file if it doesn't exist then create it and append this to it: Host localhost ForwardAgent yes So "line then new line 'tab' then text" I think its a sensitive format. I know you can do this: cat…
TheLegend
  • 6,885
629
votes
8 answers

What is the difference between /opt and /usr/local?

According to the Filesystem Hierarchy Standard, /opt is for "the installation of add-on application software packages". /usr/local is "for use by the system administrator when installing software locally". These use cases seem pretty similar. …
Patches
  • 6,632
623
votes
15 answers

What if 'kill -9' does not work?

I have a process I can't kill with kill -9 . What's the problem in such a case, especially since I am the owner of that process. I thought nothing could evade that kill option.
tshepang
  • 65,642
617
votes
4 answers

Does curl have a --no-check-certificate option like wget?

I am trying to make a curl request to one of our local development servers running a dev site with a self-signed SSL cert. I am using curl from the command line. I saw some blog posts mentioning that you can add to the list of certificates or…
cwd
  • 45,389
608
votes
26 answers

How to generate a random string?

I would like to generate a random string (e.g. passwords, user names, etc.). It should be possible to specify the needed length (e.g. 13 chars). What tools can I use? (For security and privacy reasons, it is preferable that strings are generated…
landroni
  • 10,906
607
votes
27 answers

How can I resolve a hostname to an IP address in a Bash script?

What's the most concise way to resolve a hostname to an IP address in a Bash script? I'm using Arch Linux.
Eugene Yarmash
  • 15,095
603
votes
16 answers

How to clear journalctl

I couldn't find in google any safe way to clear systemd journal. Do anyone know any safe and reliable way to do so? Let's say I was experimenting with something and my logs got cluttered with various error messages. Moreover I'm displaying my…
Łukasz Zaroda
  • 6,593
586
votes
7 answers

Scroll inside Screen, or Pause Output

I use screen for my command-line tasks while managing the servers where I work. I usually run small commands (mostly file-system tasks) but sometimes I run more extensive tasks (like DBA). The output of those tasks is important to me. Since I use…
AeroCross
  • 6,403
585
votes
10 answers

How to display `top` results sorted by memory usage in real time?

How can I display the top results in my terminal in real time so that the list is sorted by memory usage?
Theodor Coogan
  • 5,851
583
votes
11 answers

Can less retain colored output?

Can I get less not to monochrome its output? E.g., the output from git diff is colored, but git diff | less is not.
ripper234
  • 31,763
580
votes
9 answers

Can grep output only specified groupings that match?

Say I have a file: # file: 'test.txt' foobar bash 1 bash foobar happy foobar I only want to know what words appear after "foobar", so I can use this regex: "foobar \(\w\+\)" The parenthesis indicate that I have a special interest in the word right…
Cory Klein
  • 18,911
576
votes
7 answers

How do I check package version using apt-get / aptitude?

Before I install a package, I'd like to know what version I would get. How do I check the version before installing using apt-get or aptitude on Debian or Ubuntu?
user4069
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