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Old 05-09-2017, 06:30 PM   #1
orri23
LQ Newbie
 
Registered: May 2017
Posts: 3

Rep: Reputation: Disabled
A bash script that I'm trying to understand


Okay

Last edited by orri23; 05-09-2017 at 08:05 PM. Reason: Solved
 
Old 05-09-2017, 06:39 PM   #2
chrism01
LQ Guru
 
Registered: Aug 2004
Location: Sydney
Distribution: Centos 7.7 (?), Centos 8.1
Posts: 17,863

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He's trying to ensure var $fn actually has a non-empty value.
I recommend running it with debugging options thus
Code:
set -xv     # this makes the parser show you exactly what its doing as it goes

read fn
while [ "a$fn" != "a" ]
do
basename "$fn"
read fn
done
 
Old 05-09-2017, 06:47 PM   #3
hydrurga
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Registered: Nov 2008
Location: Pictland
Distribution: Linux Mint 20 MATE
Posts: 8,048
Blog Entries: 5

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Relevant: https://serverfault.com/questions/75...iable-is-empty
 
Old 05-09-2017, 07:34 PM   #4
mike acker
Member
 
Registered: Feb 2014
Location: Michigan
Distribution: Debian 10
Posts: 190

Rep: Reputation: Disabled
why not use the -z test?

Example:


Code:
#!/bin/sh
#

TEST_STRING="This has been a test"
echo "Test 1 String value is : " $TEST_STRING

if [ -z "$TEST_STRING" ]
then
      echo "Test String is empty."
else
      echo $TEST_STRING
fi

TEST_STRING=""
echo "Test 2 : Test String is empty "

if [ -z "$TEST_STRING" ]
then
      echo "Test String is empty."
else
      echo $TEST_STRING
fi

exit 0

Result:

~/Documents/Scripting $ ./test_string.sh
Test 1 String value is : This has been a test
This has been a test
Test 2 : Test String is empty
Test String is empty.
~/Documents/Scripting $

i just acquired a copy of Shell Scripting (Jason Cannon) (Amazon) which to me is very helpful. Lots of examples!
 
Old 05-10-2017, 06:47 AM   #5
rtmistler
Moderator
 
Registered: Mar 2011
Location: USA
Distribution: MINT Debian, Angstrom, SUSE, Ubuntu, Debian
Posts: 9,319
Blog Entries: 13

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@orri23, welcome to LQ.

Please do not edit your posts and remove content, especially the question or problem description. This thread is now ineffective because it makes no sense. Consider revising the original question to allow the thread to possibly be helpful to future solution seekers. Please do not repeat this behavior in the future, it doesn't help the site, it doesn't help all to increase their Linux knowledge, which is mainly why we are all here.

Best Regards,

- RT
 
Old 05-10-2017, 08:52 AM   #6
BW-userx
LQ Guru
 
Registered: Sep 2013
Location: Somewhere in my head.
Distribution: Slackware (current), FreeBSD, Win10, It varies
Posts: 9,952

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Why not use -n test?

(code example taken from @mike acker, then fixed and modified to match test prams)
Code:
#!/bin/sh
#

TEST_STRING="This has been a test"
echo "Test 1 String value is : " $TEST_STRING

if [ -n "$TEST_STRING" ] ;
then
     echo "$TEST_STRING" 
else
      echo "Test String is empty."
fi

TEST_STRING=""
echo "Test 2 : Test String is empty "

if [ -n "$TEST_STRING" ] ;
then
       echo "$TEST_STRING"
else
      echo "Test String is empty."
fi

exit 0
example
Code:
userx%slackwhere ⚡ ~ ⚡> testS="hite"
userx%slackwhere ⚡ ~ ⚡> [[ -n $testS ]] && echo "got string"
got string
7.3. Other Comparison Operators

Last edited by BW-userx; 05-10-2017 at 09:00 AM.
 
  


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