getting full path from relative path


 
Thread Tools Search this Thread
Top Forums Shell Programming and Scripting getting full path from relative path
# 1  
Old 03-14-2007
getting full path from relative path

given a relative path, how do i convert it into a full one. i.e. if i am in

/home/polypus

and i am given foo/bar then to get a full path i can just concatinate it with pwd, but what if i am given "../mama"

how do i programmatically convert:

/home/polypus and ../mama into /home/mama

in a way that will always work no matter what relative path is passed?

my first thought is to just cd to the directory and set a variable

cd $rev_path
full_path=`pwd`
cd $original_dir

it seems there must be a unix command which does this more elegantly?

thanks
# 2  
Old 03-15-2007
This is why relative paths have problems sometimes. There isn't a good way to handle absolutely any relative path, because all relative paths have an assumption:

the current working directory is "x".

You are assuming /home/polypus. Unix tools are designed to do one thing very well. It's hard to make a bulletproof tool because of the cwd assumption.

Because:
Obviously it may not be true.

So, there is no really elegant way to deal with it. You're onto one way to deal with it.
For programming, you should consider avoiding relative paths unless you want the code to work if and only if it runs from a certain directory.
# 3  
Old 03-15-2007
Suppose that I don't have room in /usr for /usr/local but I do have some room in /export. So I make a directory called /export/usr.local and it has a subdirectory called bin. And I do a "ln -s /export/usr.local /usr/local". Now I do a "cd /usr/local" then I do a "cd bin". At this point my view is that I am in /usr/local/bin and a shell with a built-in pwd command may return that path. But /usr/bin/pwd will return /export/usr.local/bin. With more symbolic links in a path, there can be more aliases like this. The value returned by /usr/bin/pwd is the physical path. With good permissions on each directory leading to the current directory, /usr/bin/pwd can return the physical path. A built-in pwd in the same shell that navigated to the current directory may be able to return the particular logical path used to arrive at the current directory. Finding all logical paths to a particular directory would be rather daunting.

Writing a program like /usr/bin/pwd is not very easy in unix. You can stat the . directory to get the inode of the current directory. Then you can open .. and stat each file in the parent directory until you find the same inode. You walk up the chain one .. at a time repeating this process until . and .. are the same inode which means you have reached /. (Actually it is harder than that because you might traverse a mount point.) This is why putting an NFS mounted filesystem in / is very unwise... every /usr/bin/pwd must contact the NFS server to perform the stat.
# 4  
Old 03-17-2007
not a 'silver bullet', but.....
Code:
#!/bin/ksh

thisFILE=$(whence ${0})
echo "here is my absolute pathname: [${thisFILE}]"

# 5  
Old 03-25-2007
thanks

thanks guys for explanations and help
Login or Register to Ask a Question

Previous Thread | Next Thread

10 More Discussions You Might Find Interesting

1. UNIX for Beginners Questions & Answers

Convert Relative path to Absolute path, without changing directory to the file location.

Hello, I am creating a file with all the source folders included in my git branch, when i grep for the used source, i found source included as relative path instead of absolute path, how can convert relative path to absolute path without changing directory to that folder and using readlink -f ? ... (4 Replies)
Discussion started by: Sekhar419
4 Replies

2. Shell Programming and Scripting

Relative path not safe

Hallo everyone, I am running an SQL-Script over KShell-Script. Thus, in the KShell-Script there are these lines: WORKPATH=$PWD/work EXPORTDIR=export_meine_datei_bitte EXPORTPATH=${WORKPATH}/${EXPORTDIR} ... db2 connect to ${DBNAME} || die "can not open database connection" db2... (9 Replies)
Discussion started by: ratnalein88
9 Replies

3. UNIX for Dummies Questions & Answers

How to convert relative path to absolute path?

Hello Everyone, I want to convert Relative Path - /home/stevin/data/APP_SERVICE/../datafile.txt to Absolute Path - /home/stevin/data/datafile.txt Is there a built-in tool in Unix to do this or any good ideas as to how can I implement this. -Steve (5 Replies)
Discussion started by: qwarentine
5 Replies

4. Shell Programming and Scripting

How to change Absolute path to Relative path

Hello, I have a doubt:- --------------------- Current script:- ################################################################################################ prefix=user@my-server: find . -depth -type d -name .git -printf '%h\0' | while read -d "" path ; do ( cd "$path" || exit $?... (4 Replies)
Discussion started by: sahil_jammu
4 Replies

5. Shell Programming and Scripting

How to extract strings from full path when full path is not fixed

/Path/snowbird9/nrfCompMgrRave1230100920.log.gz:09/20/2010 06:14:51 ERROR Error Message. /Path/snowbird6/nrfCompMgrRave1220100920.log.gz:09/20/2010 06:14:51 ERROR Error Message. /Path/snowbird14/nrfCompMgrRave920100920.log.gz:09/20/2010 06:14:51 ERROR Error Message.... (0 Replies)
Discussion started by: Shirisha
0 Replies

6. Shell Programming and Scripting

Retrieve directory path from full file path through sh

Hi, I have a file abcd.txt which has contents in the form of full path file names i.e. $home> vi abcd.txt /a/b/c/r1.txt /q/w/e/r2.txt /z/x/c/r3.txt Now I want to retrieve only the directory path name for each row i.e /a/b/c/ /q/w/e/ How to get the same through shell script?... (7 Replies)
Discussion started by: royzlife
7 Replies

7. Shell Programming and Scripting

absolute path for a script ran with relative path

I have a script in which i want to print absolute path of the same script irrespective of path from where i run script. I am using test.sh: echo "pwd : `pwd`" echo "script name: $0" echo "dirname: `dirname $0`" when i run script from /my/test/dir/struct as ../test.sh the output i... (10 Replies)
Discussion started by: rss67
10 Replies

8. Shell Programming and Scripting

how to read the relative path

suppose i ahve a shell script Nsdnet.sh inside a directory /dialp/Release/bin another file nsdnet_file.csv is under the same directory. Now in the shell script i have call a java file, which reads the csvfile from the commandline. Now when i run the file as $ ./Nsdnet.sh ./nsdnet_file.csv then... (5 Replies)
Discussion started by: priyanka3006
5 Replies

9. UNIX for Dummies Questions & Answers

Help with absolute path and relative path

I'm having problems accessing the Knoppix software on my current computer and the replacement CD I ordered hasn't arrived yet. I have a guess at what the answer would be for this question but I am not sure as I cannot test it with the software. I have to create a directory called class, and... (1 Reply)
Discussion started by: mzero
1 Replies

10. UNIX for Dummies Questions & Answers

vi - replacing a relative path with absolute path in a file

Hi, I have a file with about 60 lines of path: app-defaults/boxXYZ....... I want to change this to /my/path/goes/here/app-defaults/boxXYZ, but of course vi doesn't like the regualr :s/old/new/ command. Is there any other quick way to do this? Thanks ;) (2 Replies)
Discussion started by: Yinzer955i
2 Replies
Login or Register to Ask a Question