what is "set" and "set -u" command?

[Worapoj P.]

Dear all expertise,

What is "set" and "set -u" command? I found them in .prfile on home directory.


Thank in advance for you answer.
Worapoj

[Deepak Extross · Accepted solution]

Check out 'man ksh'

set -u will treat unset parameters as an error while substititing, rather than substituting them with a blank.

[Steve Steel]

Hi

See man page sh-posix



The set command with neither arguments nor options displays the
names and values of all shell parameters on standard output. See
also env(1).

set -u treat unset parameters as an error when substituting.

| set [{-|+}abCefhkmnopstuvx] [{-|+}o option]... [{-|+}A
name] [arg]...


Steve Steel

[Worapoj P.]

what difference between command #set and #env , output both of them look like same.

pls advise,
worapoj

[Vincent Stedema]

Hi,

running "set" without parameters does exactly the same thing as running "env". However, like Deepak and Steve pointed out, "set" can also be use to exert control over how environment variables are treated.

For example, if you issue:

#echo $UNSET_VARIABLE

a blank line will be echoed.

Now, do the following:

#set -u
#echo $UNSET_VARIABLE

"echo" will generate an error message stating that the variable UNSET_VARIABLE is not set.

HTH

Vincent

[Worapoj P.]

Dear HTH,
You meant #set do the same same #export like? For example,
#export NAME=Worapoj
#print $NAME
Worapoj

like
#set NAME_A=Worapoj_A
but
#print $NAME_A
Parameter not set.

Please advise,
Worapoj

[Vincent Stedema]

Uhmm...that's not what I meant.

"set" can be used to:

a) print environment variables (like "env")

b) tell the shell how to treat variable references. If you try to echo a variable which does not yet exist, "echo" will normally print a blank line. If you do a "set -u" first and then echo the same non-existing variable, the shell will complain about empty variable references (i.e. a reference to a variable which has no value assigned to it).

Hope this helps.

Vincent

[Worapoj P.]

Dear HTH,
Another one what difference with #set and #env , as you told is display the same thing.


Pease advise,
Worapoj

[Deepak Extross]

Hi,

set is not equivalent to export!
Steve has mentioned the syntax of set. It is typically used with the following options: {-|+}abCefhkmnopstuvx , each having a specific meaning, which you can get from the man page of ksh or sh-posix.

I think what Vincent aka devnull aka HTH (??) meant was that 'set' without any parameter will yield the same output as 'env', but this is valid ONLY IF NO PARAMETER IS PASSED to set.

[Vincent Stedema]

HTH = Hope This Helps