Variable expansion will be done by the shell in any case (in case of double-quotes). The double-quotes are to retain the embedded spaces and/or to tell the shell that the parameter exists (in case of null strings) in case of [..] construct.
You don't require the quotes in case [[..]] construct (unless you are testing strings as is).
Also, in the [[..]], globbing is not done.
In ksh88,
Code:
$ [ -z $x ] && echo HI
ksh: test: 0403-004 Specify a parameter with this command.
$ [ -z "$x" ] && echo HI
HI
$ [[ -z $x ]] && echo HI
HI
Oppss. .. i think i have misread and misplaced another concept here..... need to correct.. thanks...
but in bash
Code:
$ [ -z $x ] && echo HI
HI
$ [ -z "$x" ] && echo HI
HI
$ [[ -z $x ]] && echo HI
HI
hi, unix gurus.
i am wondering if someone can give me a clear explanation of the differneces between parentheses and brackets, both single and double.
i have heard that double parentheses (( are used for numerical expressions and that single brackets [ are used for strings. but i see... (1 Reply)
One of the senior administrators gave me a shell script to modify and it begins as follows:
if ] && ]
{more code follows}
Why the double square brackets? (10 Replies)
Hi
First apologies if this has been raised before.
I've got the following in a ksh script:
if ]
For some reason this does not work. But if I remove the double square brackets to:
if
This works.
I thought ksh supported the ]. Or is there more to it?
Thanks in advance. (3 Replies)
Hi,
I just came across an interesting shell script syntax like the one below:
] && (trap 'rm -rf ${WORK_DIR}/*.$$; echo "\n\nInterrupted !!\n\n"; exit 4' 1 2 3 15)
Can someone please explain the code snippet above?
The trap command bit is fine but ] && is the hazy part.
Generally we use an... (2 Replies)
Hi All,
I have a text file which looks like this:
computer programming
systems engineering
I want to get rid of these square brackets and also the text that is inside these brackets. So that my final text file looks like this:
computer programming
systems engineering
I am using... (3 Replies)
I wanted to compare the value inside the Squre bracket after Colon ( : ) based on any value(seperated by or operator | ) inside the variable Thread and if match found then wnated to store in output file
Input file :
20140320 00:08:43.918 INO 35] - Corporate hub is
20140320 00:08:43.918... (2 Replies)
I wanted to store the number inside the square bracket between colon( : ) and closing suqre bracket(]) in some variable.
Suppose I have lines like :
Input file :
20140320 00:08:23.846 INFO 84] - anything in line
20140320 00:08:23.846 Test 589] - Virtual and lab lab anything... (18 Replies)
Hi All,
Hope you all are doing good. Yesterday in my project i came across a scenario which i can not guess why it was working in one region and why it was not in another region. Please find my issue below.
I am using AIX version 6.0 of UNIX in my project, in shell scripting i have the... (1 Reply)
10-01-2012
.. i think i have misread and misplaced another concept here..... need to correct.. thanks...