Visit Our UNIX and Linux User Community


Problems understanding example code


 
Thread Tools Search this Thread
Top Forums Shell Programming and Scripting Problems understanding example code
# 1  
Old 07-29-2009
Problems understanding example code

I am really new to UNIX and programming in general and so apologies if this thread is a bit simple.

I have searched and found a piece of sample code for a training program I am currently undertaking, but seeing as I am relatively new, I dont completely understand how it works.

Here is the code:

file=$1
set -- $(ls -ld $file)

perms=$1
owner=$3

[[ "$perms" = ?r???????? ]] && owner_read=YES
[[ "$perms" = ??w??????? ]] && owner_write=YES
[[ "$perms" = ???x?????? ]] && owner_exec=YES

[[ "$perms" = ????r????? ]] && group_read=YES
[[ "$perms" = ?????w???? ]] && group_write=YES
[[ "$perms" = ??????x??? ]] && group_exec=YES

[[ "$perms" = ???????r?? ]] && world_read=YES
[[ "$perms" = ????????w? ]] && world_write=YES
[[ "$perms" = ?????????x ]] && world_exec=YES

echo "perms: $perms"
echo "OWNER $owner ${owner_read:-NO} ${owner_write:-NO} ${owner_exec:-NO}"
echo "GROUP ${group_read:-NO} ${group_write:-NO} ${group_exec:-NO}"
echo "WORLD ${world_read:-NO} ${world_write:-NO} ${world_exec:-NO}"
Basically I understand how the script works generally, but I am just wondering whether the [[ ]] is equal to a shorthand if statement?

Also is ${owner_read:-NO} checking if the result from the above statement is null and then if so printing "NO"?

Sorry if this is a bit simple.

Thanks for any help.
# 2  
Old 07-29-2009

Previous Thread | Next Thread
Test Your Knowledge in Computers #656
Difficulty: Medium
Microsoft and IBM began developing OS/2 as an alternative to Unix.
True or False?

10 More Discussions You Might Find Interesting

1. Programming

Understanding Assembly Code

As the title suggests, I want to better understand the following assembly code: section .text global main ; must be declared for linker (gcc) main: ; tell linker entry point mov edx, len ; message length mov ecx, msg ; message to write... (2 Replies)
Discussion started by: Azrael
2 Replies

2. UNIX for Dummies Questions & Answers

Understanding bash code

I am not able to understand below line in unix bash shell.Could anyone explain what it will do result="${path1}/*${var1}*${var2}*wssreligibleitem*.csv" path1 is defined and it is a directory path var1 is defined and it holds string value like abc var2 is defined and it holds string value like... (6 Replies)
Discussion started by: vamsi.valiveti
6 Replies

3. Shell Programming and Scripting

Help with perl code understanding

Hi, I need to understand below perl code, can some one advise me. perl -MDate::Parse -e'BEGIN{$main::now=time;$main::old=(time-60*30)}' -nE'if(/^(\w+\s+\d+\s+\d+:\d+:\d+)/) {$t=str2time $1; $t > $old && $t < $now && print}' (1 Reply)
Discussion started by: learnbash
1 Replies

4. Programming

Understanding perl code

What is the difference between the two statements below? A: $a->{"$fruit"}->{"$color"}->{size} = $size B: $size = $a->{"$fruit"}->{"$color"}->{size} Please assist. Thanks! (0 Replies)
Discussion started by: onlinelearner02
0 Replies

5. Shell Programming and Scripting

Help understanding some Perl code.

Well, I found myself trying to fix some Perl code (Ive never done any Perl in my life) and I pinpointed the place where the bug could be. But to be sure I have to know what does a few line of code mean: $files_lim =~ (/^\d*$/) $files_lim =~ (/^\d*h$/) $files_age =~ s/h// The code where... (2 Replies)
Discussion started by: RedSpyder
2 Replies

6. Shell Programming and Scripting

Help understanding Perl code.

Well, I found myself trying to fix some Perl code (Ive never done any Perl in my life) and I pinpointed the place where the bug could be. But to be sure I have to know what does a few line of code mean: $files_lim =~ (/^\d*$/) $files_lim =~ (/^\d*h$/)$files_age =~ s/h//The code where this was... (0 Replies)
Discussion started by: RedSpyder
0 Replies

7. Programming

Problems understanding pipes

I am trying to create a csh clone, but am having problems implementing piped commands. Specifically, the below code simply hangs after input of ls | grep <text> It does however filter the output and display it correctly, but it appears that grep hasn't exited and my shell never comes back to the... (16 Replies)
Discussion started by: ab_tall
16 Replies

8. UNIX Desktop Questions & Answers

Understanding the code

hello all, May i know what is this "DEBUG_ME $DEBUG_CMD main" doing in the below code. I am confused with alias also "alias DEBUG_ME='#'". Thanks for your help. set -x alias DEBUG_ME='#' if ; then . /product/apps/informatica/v7/pc/ExtProc/debug.ksh "$1" fi # Declaring the... (1 Reply)
Discussion started by: Ariean
1 Replies

9. UNIX for Dummies Questions & Answers

Problems understanding example code

I am really new to UNIX and programming in general and so apologies if this thread is a bit simple. I have searched and found a piece of sample code for a training program I am currently undertaking, but seeing as I am relatively new, I dont completely understand how it works. Here is the... (6 Replies)
Discussion started by: Makaer
6 Replies

10. UNIX for Dummies Questions & Answers

Understanding Code in IF LOOP

Hello All, I would like to know and understand the difference between the below 3 IF loops and also if possible what are the different other parameters i could use other than those mentioed in the below lF LOOP conditions, appreciate your help. Thanks, Sam. (1 Reply)
Discussion started by: Ariean
1 Replies

Featured Tech Videos