12-09-2009
Quote:
can one of you explain me
1. where to use spaces and where not to?
2. some time I see double square brackets used [[ ...]] when should I use these?
3.should there be a space between variable and value in condition like
<variable><space><operator><space><value>
4.when should i use either single/double quotes around variables and values?
5. should 'then' be used after every conditinal statement ?
Some very general answers: -
1) Use spaces as you show in question 3, not during assignments such as X=12.
2) I think there are two versions of ksh in general use, 88 and 93? [[ ]] is ksh 88 whereas [ ] is ksh 93 Most commercial UNIX environments still use 88 somewhat inexplicably. The company I work for is only 5 years old but uses 88!!
3) Yes for conditional statements.
4) Big subject. Quoting is one of the trickiest subjects in shell scripting. On a simple level if a string contains spaces you probably want to quote it but not always.
5) In 88 at least you want to put a "then" after an if although if statements are not the only types of conditional statements,
Experiment
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LEARN ABOUT OPENDARWIN
times
times(1) User Commands times(1)
NAME
times - shell built-in function to report time usages of the current shell
SYNOPSIS
sh
times
ksh
times
DESCRIPTION
sh
Print the accumulated user and system times for processes run from the shell.
ksh
Print the accumulated user and system times for the shell and for processes run from the shell.
On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:
1. Variable assignment lists preceding the command remain in effect when the command completes.
2. I/O redirections are processed after variable assignments.
3. Errors cause a script that contains them to abort.
4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari-
able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not
performed.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
SEE ALSO
ksh(1), sh(1), time(1), attributes(5)
SunOS 5.10 15 Apr 1994 times(1)