sorry for the late reply, just been busy work and all
i have added to my script if the tar file already exists in the "archived_projects" folder do not over write and also the size and file count
---------- Post updated at 08:27 AM ---------- Previous update was at 06:10 AM ----------
i think thats a good idea condensing the remove commands to one, i will do that in my next revision, but what bakunin said about you dont need to add the return code to the if statement, i dont seem to get it as for every command you type if it returns 0 (success) or 1-255 (failed) it will either do then or the else statement
but you havnt put in any return code so how does it know whether the command before has succeeded or failed?
Last edited by robertkwild; 04-21-2016 at 11:52 AM..
i think thats a good idea condensing the remove commands to one, i will do that in my next revision, but what bakunin said about you dont need to add the return code to the if statement, i dont seem to get it as for every command you type if it returns 0 (success) or 1-255 (failed) it will either do then or the else statement
but you havnt put in any return code so how does it know whether the command before has succeeded or failed?
OK, short introduction to the intractes of "if":
"if" is followed by a (any) command and it executes first this command, then the "then...."-part if the command returns RC 0 or the "else..."-part, if not. This is always the case. For instance:
Here, the command "some_command" is executed. If it returns 0 the then-part is executed, if it returns something else the "else"-part is executed.
You may ask yourself where this:
now comes from because there seems no command to be involved: wrong. In fact there is a command involved and it is called "test". "test" does all kinds of tests: integer comparisons, string comparisons and tests for the existence (or certain attributes) of files and it returns a RC of 0 for the comparisons being (logically) true and an RC <> 0 for comparisons being logically false.
Historically, in the first UNIX versions the construct looked like this (and you may see this still in some very old scripts):
or maybe:
You see, the expression to be evaluated consists just of arguments to "test". "test", is still there, i suggest to read the man page of it.
But because this didn't look like the programming languages the inventors of UNIX knew (they were all programmers, after all), they created a device which made it look more like what they were accustomed to: they created a symbolic link from /usr/bin/test to /usr/bin/[ - in fact "[" is a possible filename - and the line now looked like this:
In some variants of UNIX (HP-Ux, if i remember right) this link still exists.
That was actually better but it looked like a bracket was opened and never closed. So the final change to /usr/bin/test was that it expected a "]" as the last argument if it was called as "[" - and this created the look we know today:
Notice, that for this reason the following won't work:
because the last parameter now would be "0]", and the expected final "]" would be missing. Try it, you will see that it leads to a syntax error - for the reasons stated above. The following weird-looking construct, though, works perfectly:
The last step in the development was that programmers of UNIX shells (and i think David Korn with his Korn shell was the first) noticed that "test" and its equivalent was called so often that they made it a shell built-in. This will prevent the necessity of loading and starting an external executable (time-consuming activities) and is a speed optimisation. Still, the buil-in "[" works the same as the external /usr/bin/test (again, with the exception of expecting "]" as the last argument) as the man page for the shell will tell you.
But because this didn't look like the programming languages the inventors of UNIX knew (they were all programmers, after all), they created a device which made it look more like what they were accustomed to: they created a symbolic link from /usr/bin/test to /usr/bin/[ - in fact "[" is a possible filename - and the line now looked like this:
In some variants of UNIX (HP-Ux, if i remember right) this link still exists.
That was actually better but it looked like a bracket was opened and never closed. So the final change to /usr/bin/test was that it expected a "]" as the last argument if it was called as "[" - and this created the look we know today:
... ... ...
I hope this helps.
bakunin
The POSIX standards require that both test and [ (and all other standard utilities except special built-ins) exist as stand-alone utilities (not just as shell built-ins). This allows them to be used as command arguments to the env, find -exec, nice, nohup, time, and xargs utilities.
The [ expression ] form of the test utility was actually added to UNIX systems before symlinks. On many UNIX and UNIX-like systems, the test and [ utilities are hard links to the same executable file instead of one of them being a symlink or both of them being separate executables.
as you said then is equal to 0 and else is not equal to 0?
many thanks
rob
No! You can't have an if statement without a then clause. But, you can do it as I suggested back in post #16 in this thread:
Note the exclamation point in red in the if statement. That reverses the exit status of the given command (tar in this case) so that if the command fails (exits with a non-zero exit status) it will execute the then clause and if the command succeeds (i.e., exits with zero exit status) it will execute the else clause if there is one.
No. The ! keyword in the shell doesn't MEAN anything. It DOES something. As I said before, it "reverses the exit status of the given command (tar in this case) so that if the command fails (exits with a non-zero exit status) it will execute the then clause and if the command succeeds (i.e., exits with zero exit status) it will execute the else clause if there is one.
Look at each of the following if statements and try to determine what the output will be. Then run the command and see if it did what you expected:
HI Guys,
I have some 8 files with different name and extensions. I need to check if they are present in a specific folder or not and also want that script to show me which all are not present. I can write if condition for each file but from a developer perspective , i feel that is not a good... (3 Replies)
1. The problem statement, all variables and given/known data:
The task is to create a script that would reproduce the output of 'du' command, but in a different way: what 'du' does is:
<size> <folder name>and what is needed is
<folder name> <size>We need to show only 10 folders which are the... (3 Replies)
Good day, everyone!
I'm very new to bash scripting. Our teacher gave us a task to create a script that basically does the same job the 'du' command does, with the difference that 'du' command gives an output in the form of
<size> <folder name>and what we need is
<folder name> <size>As for... (1 Reply)
Hi All,
I have to requirement to write a shell script to move file from one folder (A) to another five folder (B,C,D,E,F) and destination folder should be blank. In not blank just skip.
This script will run as a scheduler every 2 minutes. It will check number of files in folder A and move 1 to... (9 Replies)
I would like to confirm my file.tar is been tar-ed correctly before I remove them. But I have very limited disc space to untar it.
Can I just do the listing instead of actual extract it? Can I say confirm folder integrity if the listing is sucessful without problem?
tar tvf file1.tar
... (1 Reply)
Hi all,
I have a tar file and inside that tar file is a folder with additional tar.gz files. What I want to do is look inside the first tar file and then find the second tar file I'm looking for, look inside that tar.gz file to find a certain directory. I'm encountering issues by trying to... (1 Reply)
I have 1000's of directories which is named as numbers. Each directory contains multiple files. Each of these directories have a file named "att". I need to rename all the att files by adding the directory name followed by "_" then att for each of the directories.
Directories
120
att... (2 Replies)
I have in directory /media/AUDIO/WAVE many .mp3 files with names like:
my filename_01of02.mp3
my filename_02of02.mp3
Your File_01of06.mp3
Your File_02of06.mp3
etc....
In the same directory, /media/AUDIO/WAVE, I have many folders with names like
9780743579490
9780743579491
etc..
Inside... (7 Replies)
I have written a shell script to perform backups using tar, rsync and optionally utilise lvm snapshots. The script is not finished but is in a working state and comments/descriptions are poor.
I would greatly appreciate any criticism and suggestions of the script to help improve my own learning... (0 Replies)
Hi.
I'm trying to copy multiple folders from the remote machine to the local machine. I wrote a batch file to run an ftp window.
The problem I am having is that the only command to copy files is mget *, and this copies only files, not folders.
For example, ftp ts555
cd ts555/test
' test... (5 Replies)