Linux command to "link" files - linux

When I do "ls -lrt", there is a file that is listed and I want to create link for example,
myfile.config -> /users/yue/home/logs/myfile.config
When making changes in myfile.config it also affects the file in
/users/yue/home/logs/myfile.config.
What command in linux allows for that?
Also, what is this called?

the command is called ln (link )
the basic form is ln pathtosource pathtotarget
here is a nice URL that talks about it http://www.computerhope.com/unix/uln.htm

Figured it out,
Its actually "ln -s " command

Related

Does SCP command works for non-empty directory, too?

Is it possible to copy a non-empty directory from a local to remote system?
with SCP command or another thing?
Yes you can, you just need to add -r flag for directories.
You can check scp manual online scp manual or you can check this stackoverflow link
It is easy :)
The command to copy a directory is much like as when copying files. The only difference is that you need to use the -r flag for recursive.
To copy a directory from a local to remote system, use the -r option:
enter image description here
The -r flag should solve your problem according to the man pages.

"Spoof" File Extension In Bash

Is there a way to "spoof" the file extension of a file in bash for consumption by another program? I can think of doing some shell scripting and making lots of soft-links, but that isn't very scalable.
Let's imagine I have a program I'm trying to use that requires input files to be of a specific file extension, and it has no method of turning off this check.
You could make a fifo with the requisite extension and cat any other file type into it. So, if your crazy program needs to see files that end in .funky, you can do this:
mkfifo file.funky
cat someotherfile > file.funky &
someprogram file.funky
Create a symbolic link for each file you want to have a particular extension, then pass the name of the symlink to the command.
For example suppose you have files with names of the form *.foo and you need to refer to them with extensions of .bar:
for file in *.foo ; do
ln -s $file _$$_$file.bar
done
I precede each symlink name with _$$_ to avoid the possibility of colliding with an existing file name (you don't want to do ln -s file.foo file.bar if file.bar already exists).
With a little more programming, your script can keep track of which symlinks it created and, if you like, clean them up after executing the command.
This assumes, as you stated in the question, that the command can't be forced to accept a different extension.
You could, without too much difficulty, create a wrapper script that replaces the command in question, creating the symlinks, invoking the command, and cleaning up after itself automatically.

Possible to symlink a file to a web url?

We currently have a challenge where the ideal solution would be to symlink a file to a web URL...
image.jpg -> http://www.host.com/images/image.jpg
Is this possible?
Maybe a named pipe that you feed with a wget for the file?
Edit - Not wget. You can work with linx -dump. So -
mkfifo reddit
links -dump reddit.com > reddit
cat reddit
There are several nice and interesting solutions here. I especially like #ArjunShankar's fuse solution. In the spirit of keeping it simple though, perhaps a file in /etc/cron.daily with
#!/bin/sh
cd /your/dir && wget -N http://www.host.com/images/image.jpg
would be a lot simpler and Good Enough(TM)?
On mac I successfully used this great tool by maxogden, which also using FUSE:
https://github.com/maxogden/mount-url
brew install osxfuse
npm install -g mount-url
Then
mount-url "https://url-to-10-gb-video-file-on-some-external-cloud-storage/video.mp4?xxx=yyy"
This would create a symlink for the file named video.mp4 in the current directory.
Not too fast access speed, but works.

Linux SoftLink to applications and execution

I have created a softlink to an application using the following command:
ln -s sourcedir/Application somedir/ApplicationSoftLink
But I do not know how to start the application using the softlink. My understanding of a softlink is that it is the same as a shortcut in Windows, you just double-click the shortcut and the application will launch. However, when I tried to ./ApplicationSoftLink the application would not start.
Could someone please provide some assistance?
ln -s sourcedir/Application somedir/ApplicationSoftLink probably puts the wrong path in your symbolic link.
Try:
ln -s $PWD/sourcedir/Application somedir/ApplicationSoftLink
Were you in somedir when you tried running ./ApplicationSoftLink?
I think what you want to do is create the link in some directory in your path, so you don't have to say where the file is at all. You can type
echo $PATH
to find out what's in your path. /usr/local/bin is a good choice for things like this.
is sourcedir/Application executable?
when I tried to "./ApplicationSoftLink" the application would not
start.
Is there any error message?
were you typing ./ApplicationSoftLink under "somedir"?
or try ln -s /absolute/path/sourcedir /absolute/path/you/want/somedir/myApp
then under somedir/myApp/ run ./Application

How can I symlink a file in Linux? [closed]

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I want to make a symbolic link in Linux. I have written this Bash command where the first path is the folder I want link into and the second path is the compiled source.
ln -s '+basebuild+'/IpDome-kernel/kernel /home/build/sandbox/gen2/basebuild/IpDome-kernel/kernal
Is this correct?
To create a new symlink (will fail if symlink exists already):
ln -s /path/to/file /path/to/symlink
To create or update a symlink:
ln -sf /path/to/file /path/to/symlink
ln -s TARGET LINK_NAME
Where the -s makes it symbolic.
ln -s EXISTING_FILE_OR_DIRECTORY SYMLINK_NAME
ln -s target linkName
You can have a look at the man page here:
http://linux.die.net/man/1/ln
(Because an ASCII picture is worth a thousand characters.)
An arrow may be a helpful mnemonic, especially since that's almost exactly how it looks in Emacs' dired.
And big picture so you don't get it confused with the Windows' version
Linux:
ln -s target <- linkName
Windows:
mklink linkName -> target
You could also look at these as
ln -s "to-here" <- "from-here"
mklink "from-here" -> "to-here"
The from-here should not exist yet, it is to be created, while the to-here should already exist (IIRC).
(I always get mixed up on whether various commands and arguments should involve a pre-existing location, or one to be made.)
EDIT: It's still sinking in slowly for me; I have another way I've written in my notes.
ln -s (target exists) (link is made)
mklink (link is made) (target exists)
ln -s source_file target_file
http://unixhelp.ed.ac.uk/CGI/man-cgi?ln
To the original question:
'ln -s '+basebuild+'/IpDome-kernel/kernel /home/build/sandbox/gen2/basebuild/IpDome-kernel/kernal'
This will indeed create a symbolic link (-s) from the file/directory:
<basebuild>/IpDome-kernel/kernel
to your new link
/home/build/sandbox/gen2/basebuild/IpDome-kernel/kernal
Here's a few ways to help you remember:
First, there's the man page for ln. You can access this via searching "man ln" in google, or just open a terminal window and type man ln and you'll get the same information. The man page clearly states:
ln [OPTION]... [-T] TARGET LINK_NAME (1st form)
If having to search or read through a man page every time isn't for you, maybe you'll have an easier time remembering that all nix commands work the same way:
cp /file/that/exists /location/for/new/file
mv /file/that/exists /location/its/moving/to
ln /file/that/exists /the/new/link
cp copies a file that currently exists (the first argument) to a new file (the second argument).
mv moves a file that currently exists (the first argument) to a new place (the second argument)
Likewise ln links a file that currently exists (the first argument) to a new link (the second argument)*
The final option I would like to suggest is you can create your own man pages that are easy to read and easy (for you) to find/remember. Just make a simple shell script that gives you the hint you need. For example♦:
In your .bash_aliases file you can place something like:
commandsfx() {
echo "Symlink: ln -s /path/to/file /path/to/symlink"
echo "Copy: cp /file/to/copy /destination/to/send/copy"
}
alias 'cmds'=commandsfx
Then when you need it, from the command line just type cmds and you'll get back the proper syntax in a way you can quickly read and understand it. You can make these functions as advanced as you'd like to get what what information you need, it's up to you. You could even make them interactive so you just have to follow the prompts.. something like:
makesymlink() {
echo "Symlink name:"
read sym
echo "File to link to:"
read fil
ln -s $fil $sym
}
alias 'symlink'=makesymlink
* - well obviously they can all take different parameters and do different things and can work on files as well as directories... but the premise is the same
♦ - examples using the bash shell
ln [-Ffhinsv] source_file [target_file]
link, ln -- make links
-s Create a symbolic link.
A symbolic link contains the name of the file to which it is linked.
An ln command appeared in Version 1 AT&T UNIX.
Creating Symbolic links or Soft-links on Linux:
Open Bash prompt and type the below mentioned command to make a symbolic link to your file:
A) Goto the folder where you want to create a soft link and typeout the command as mentioned below:
$ ln -s (path-to-file) (symbolic-link-to-file)
$ ln -s /home/user/file new-file
B) Goto your new-file name path and type:
$ ls -lrt (To see if the new-file is linked to the file or not)
Example:
user#user-DT:[~/Desktop/soft]# ln -s /home/user/Desktop/soft/File_B /home/user/Desktop/soft/File_C
user#user-DT:[~/Desktop/soft]# ls -lrt
total 0
-rw-rw-r-- 1 user user 0 Dec 27 16:51 File_B
-rw-rw-r-- 1 user user 0 Dec 27 16:51 File_A
lrwxrwxrwx 1 user user 31 Dec 27 16:53 File_C -> /home/user/Desktop/soft/File_B
Note: Where, File_C -> /home/user/Desktop/soft/File_B Means, File_C is symbolically linked to File_B
ln -s sourcepath linkpathname
Note:
-s makes symbolic links instead of hard links
This is Stack Overflow so I assume you want code:
All following code assumes that you want to create a symbolic link named /tmp/link that links to /tmp/realfile.
CAUTION: Although this code checks for errors, it does NOT check if /tmp/realfile actually exists ! This is because a dead link is still valid and depending on your code you might (rarely) want to create the link before the real file.
Shell (bash, zsh, ...)
#!/bin/sh
ln -s /tmp/realfile /tmp/link
Real simple, just like you would do it on the command line (which is the shell). All error handling is done by the shell interpreter. This code assumes that you have a working shell interpreter at /bin/sh .
If needed you could still implement your own error handling by using the $? variable which will only be set to 0 if the link was successfully created.
C and C++
#include <unistd.h>
#include <stdio.h>
int main () {
if( symlink("/tmp/realfile", "/tmp/link") != 0 )
perror("Can't create the symlink");
}
symlink only returns 0 when the link can be created. In other cases I'm using perror to tell more about the problem.
Perl
#!/usr/bin/perl
if( symlink("/tmp/realfile", "/tmp/link") != 1) {
print STDERR "Can't create the symlink: $!\n"
}
This code assumes you have a perl 5 interpreter at /usr/bin/perl. symlink only returns 1 if the link can be created. In other cases I'm printing the failure reason to the standard error output.
If you are in the directory where you want to create symlink, then ignore second path.
cd myfolder
ln -s target
It will create symlink of target inside myfolder.
General syntax
ln -s TARGET LINK_NAME
I'd like to present a plainer-English version of the descriptions already presented.
ln -s /path-text/of-symbolic-link /path/to/file-to-hold-that-text
The "ln" command creates a link-FILE, and the "-s" specifies that the type of link will be symbolic. An example of a symbolic-link file can be found in a WINE installation (using "ls -la" to show one line of the directory contents):
lrwxrwxrwx 1 me power 11 Jan 1 00:01 a: -> /mnt/floppy
Standard file-info stuff is at left (although note the first character is an "l" for "link"); the file-name is "a:" and the "->" also indicates the file is a link. It basically tells WINE how Windows "Drive A:" is to be associated with a floppy drive in Linux. To actually create a symbolic link SIMILAR to that (in current directory, and to actually do this for WINE is more complicated; use the "winecfg" utility):
ln -s /mnt/floppy a: //will not work if file a: already exists
To create a symbolic link /soft link, use:
ln -s {source-filename} {symbolic-filename}
e.g.:
ln -s file1 link1
Links are basically of two types:
Symbolic links (soft): link to a symbolic path indicating the abstract location of another file
Hard links: link to the specific location of physical data.
Example 1:
ln /root/file1 /root/file2
The above is an example of a hard link where you can have a copy of your physical data.
Example 2:
ln -s /path/to/file1.txt /path/to/file2.txt
The above command will create a symbolic link to file1.txt.
If you delete a source file then you won't have anything to the destination in soft.
When you do:
ls -lai
You'll see that there is a different inode number for the symlinks.
For more details, you can read the man page of ln on your Linux OS.
There are two types of links:
symbolic links: Refer to a symbolic path indicating the abstract location of another file
hard links: Refer to the specific location of physical data.
In your case symlinks:
ln -s source target
you can refer to http://man7.org/linux/man-pages/man7/symlink.7.html
you can create too hard links
A hard link to a file is indistinguishable from the original directory entry; any changes to a file are effectively independent of the name used to reference the file. Hard links may not normally refer to directories and may not span file systems.
ln source link
I find a bit confusing the terminologies "target" and "directory" in the man information.
The target is the folder that we are symlinking to and the directory the actual symlink (not the directory that you will be symlinking to), if anyone is experiencing the same confusion, don't feel alone.
This is my interpretation of creating a Symlink (in linux):
ln -s /FULL/PATH/FOLDER-OR-FILE-SYMLINKING-TO NAME-OF-YOUR-SYMLINK
You can navigate to the folder where you want to create the symlink and run the command or specify the FULL PATH for your symlink instead of NAME-OF-YOUR-SYMLINK.
cd /FULL/PATH/TO/MY-SYMLINK-PARENT-FOLDER
ln -s /FULL/PATH/FOLDER-OR-FILE-SYMLINKING-TO NAME-OF-YOUR-SYMLINK
OR
ln -s /FULL/PATH/FOLDER-OR-FILE-SYMLINKING-TO /FULL/PATH/TO/MY-SYMLINK-PARENT-FOLDER/NAME-OF-YOUR-SYMLINK
I hope this helps to those (still) slighly confused.
How to create symlink in vagrant.
Steps:
In vagrant file create a synced folder. e.g config.vm.synced_folder "F:/Sunburst/source/sunburst/lms", "/source"
F:/Sunburst/source/sunburst/lms :- where the source code, /source :- directory path inside the vagrant
Vagrant up and type vagrant ssh and go to source directory e.g cd source
Verify your source code folder structure is available in the source directory. e.g /source/local
Then go to the guest machine directory where the files which are associate with the browser. After get backup of the file. e.g sudo mv local local_bk
Then create symlink e.g sudo ln -s /source/local local. local mean link-name (folder name in guest machine which you are going to link)
if you need to remove the symlink :- Type sudo rm local

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