[SOLVED] Shell script: condition always met ?

x111 · 09-23-2010, 11:59 PM

Hi everybody. I'm learning to write some shell scripts to work with the system. Now I'm on a script to mount a device by its full path.
Here is what I've done so far:

Code:

#! /bin/sh
BASEDIR="/mnt"
PARTITION=$1 # Get device path by 1st parameter

PTYPE=`blkid $PARTITION -o value -s TYPE 2>&1` #Get partition type
echo "Partition: $PARTITION, type: $PTYPE"
if [ $PTYPE ] ; then # Mountable partition
	MOUNTNAME=`echo $PARTITION | egrep -o [h,s]d.[0-9]+`
	MOUNTPOINT="$BASEDIR/$MOUNTNAME"
	MOUNTOPS=""
	if [ $PTYPE=="ntfs" ] ; then # If this is an ntfs, apply a special option
		MOUNTOPS="-t ntfs-3g"
	fi
	mkdir -p $MOUNTPOINT
	echo "Mount options for $PARTITION: $MOUNTOPS"
	mount $MOUNTOPS $PARTITION $MOUNTPOINT
	echo $MOUNTPOINT" mounted."

else # blkid returned nothing, usually this is a "container" partition and not mountable
	echo "Unknown type"
fi

exit 0

But when it comes to the type check, the condition on ntfs type is always met, which means that the mount options is always "-t ntfs-3g", regardless of what type the partition is.

Here the output of the command on an ext3 partition:
# mount-any /dev/hda8

Code:

Partition: /dev/hda8, type: ext3
Mount options for /dev/hda8: -t ntfs-3g
NTFS signature is missing.
Failed to mount '/dev/hda8': Invalid argument
The device '/dev/hda8' doesn't have a valid NTFS.
Maybe you selected the wrong device? Or the whole disk instead of a
partition (e.g. /dev/hda, not /dev/hda1)? Or the other way around?
/mnt/hda8 mounted.

I've tried replacing

Code:

if [ $PTYPE=="ntfs" ] ; then

with

Code:

if [ $PTYPE==ntfs ] ; then

But still no luck.
So anyone please tell me what I'm doing wrong and how to set this condition checking right.
Thanks for all your help and suggestion.

smoker · 09-24-2010, 12:15 AM

You need spaces in the condition.
Try :

Code:

if [ "$PTYPE" == "ntfs" ] ; then

http://mywiki.wooledge.org/BashGuide..._and_.5B.5B.29

x111 · 09-24-2010, 12:45 AM

Quote:

Originally Posted by smoker

You need spaces in the condition.
Try :

Code:

if [ "$PTYPE" == "ntfs" ] ; then

http://mywiki.wooledge.org/BashGuide..._and_.5B.5B.29

Oh, thanks for your answer, smoker. It is quick and accurate. Now I have it working.

By the way, why there're "==" and "=", and "-eq" just for comparision. Do you think that bash syntax is not intuitive enough, at least for a beginner.

chrism01 · 09-24-2010, 12:53 AM

Basically (as you'll see by reading around)

Code:

-eq  is for comparing numbers
=    is for comparing strings (old school)
==   is for comparing strings (modern method)

either of the latter will work for strings.
The shell (ksh, bash) is more or less context sensitive, but I'd stick to '==' for clarity.

smoker · 09-24-2010, 05:27 PM

In addition to Chris's answer, there are different effects caused by the number of square brackets and double quotes around the condition. At least as far as the variable is concerned. See the TLDP advanced bash scripting guide.