[SOLVED] BASH help

niharikaananth · 08-05-2012, 12:00 PM

Hi All,
I am newbie in shell scripting, So need your help for this small script.

Code:

$ cat dir_check 
#!/bin/bash
dir="mydir"
###Check whether directory is exist or not###
if [ -d $dir ]; then
echo "The $dir directory is exist, so changing directory to $dir directory"
cd $dir
else
###Create directory and change directory##
echo "The $dir directory does not exist, so creating $dir and changing to $dir directory"
mkdir $dir && cd $dir
fi

1) It is not changing to mydir directory when the directory is exist.
2) just creating the directory but unable to cd while directory does not exist.

Code:

$ pwd
/tmp/test
$ ls
dir_check  mydir
$ rm -rf mydir
$ ls
dir_check
$ bash dir_check 
The mydir directory does not exist, so creating mydir and changing to mydir directory
$ pwd
/tmp/test
$ ls
dir_check  mydir
$ bash dir_check 
The mydir directory is exist, so changing directory to mydir directory
$ pwd
/tmp/test

Thanks in advance for your kind help

KinnowGrower · 08-05-2012, 12:17 PM

Code:

if [ -d $dir ]; then

Semicolon ";" in the if statement is the culprit. Remove it and its fine.

niharikaananth · 08-05-2012, 12:47 PM

Thanks KinnowGrower,
I removed ";"

Code:

if [ -d $dir ] then

And getting the following error

Code:

$ bash -n dir_check 
dir_check: line 7: syntax error near unexpected token `else'
dir_check: line 7: `else

Then moved "then" to next line.

Code:

if [ -d $dir ]
then
$ bash -n dir_check
$

But still unable to change directory!

Code:

$ pwd
/tmp/test
$ ls
dir_check  mydir
$ bash dir_check 
The mydir directory is exist, so changing directory to mydir directory
$ pwd
/tmp/test

414N · 08-05-2012, 12:50 PM

Quote:

Originally Posted by KinnowGrower

Code:

if [ -d $dir ]; then

Semicolon ";" in the if statement is the culprit. Remove it and its fine.

No, the semicolon is fine if you put the "then" keyword on the same line of if. If you remove it you have to put "then" on the next line.
The problem is that the cd command gets executed in a subprocess of the shell, so that subprocess changes directory but not the parent shell (i.e. the one you used to launch the script).
Try running the script as

Code:

. dir_check

or

Code:

source dir_check

The source (or .) directive forces the shell to execute the commands inside the script in the current process, without forking a new shell.

niharikaananth · 08-05-2012, 01:28 PM

Thanks 414N,

Quote:

. dir_check

or

Quote:

source dir_check

The above both are working fine as what I had expected.
But how should be the crontab entry for this if we add some backup(rsync/tar) commands in the middle?
should this be like below?

Code:

01 00 * * * /path/of/script/file >/dev/null 2>&1

Because since below are not working, I can't guess that above crontab entry works for changing directory.

Code:

chmod +x /path/of/script/file
./path/of/script/file   --->Unable to change directory!

So could you please post also about crontab entry which can change the directory.

414N · 08-05-2012, 02:19 PM

If you need to perform some rsync/tar work inside a specific directory then just cd to the directory and run the backup commands inside the script. You don't need to care about "sourcing" (as in using the source keyword) the script to alter the current directory of the parent shell process.
To explain better, suppose you've got this simple script (foobar.sh) which executes a tar command inside the /foo/bar directory:

Code:

#!/bin/sh

cd /foo/bar
tar cjf foobar.tar.bz2 *

When you launch the script on the command line, the shell (read: parent process) creates a new shell process (read: child process) containing a copy of its environment (including current directory information) and the script gets executed inside this subprocess. Then:

the parent process goes to sleep until the child terminates;
all changes performed by the script to the shell environment (such as a cd command) are indeed applied only to the child shell process and will not outlive it;
the current directory is then changed to /foo/bar and the tar command is performed there;
when the child process terminates (after the tar line) it is destroyed and control returns to the parent shell process which awakes from its sleep

You can test this behavior adding simple echo inside your scripts before and after the "cd"s command:

Code:

echo "Current dir is $(pwd)"
cd /some/dir/somewhere/in/a/distant/galaxy/long/long/time/ago
echo "Current dir is $(pwd)"

You should see that the "cd" command is indeed performed, but a pwd command executed after the script will show no change in current directory.

niharikaananth · 08-07-2012, 05:11 AM

Hi 414N,
Sorry for the late reply. It is working fine using

Code:

$. dir_check
$source dir_check
$bash dir_check
$./dir_check
and
also through crontab

Code:

#!/bin/bash
today=$(date '+%Y-%m-%d')
dir="/data/my_scripts/mydir"
echo $(date) > /tmp/date
###Check whether directory is exist or not###
if [ -d $dir ]; then
echo "The $dir directory is exist, so changing directory to $dir directory"
cd $dir
echo "Current dir is $(pwd)"
sleep 5
tar -cjf tmp.$today.tar.bz2 /tmp
else
###Create directory and change directory##
echo "The $dir directory does not exist, so creating $dir and changing to $dir directory"
mkdir $dir && cd $dir
echo "Current dir is $(pwd)"
sleep 5
tar -cjf tmp.$today.tar.bz2 /tmp
fi

Thanks and Regards

chrism01 · 08-07-2012, 08:28 PM

'sleep 5' is redundant