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Problem with -s option in IF

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Top Forums Shell Programming and Scripting Problem with -s option in IF
# 8  
Old 11-05-2013
One thing you dont say: the shell you use and OS version... HP-UX used by default ksh I dont have anymore HP-UX 11.23 and above so cannot confirm all cases but till 11.23 ksh was default with posix shell... on 11.11 ksh is NOT ksh93 compliant ( Is a ksh88...)
You seem to mix diverse shell syntax this if can work sometime is sure to give you great issues: Once a shell chosen stick to its syntax, dont mix!
# 9  
Old 11-05-2013
Quote:
Originally Posted by HIMANSHU SOOD
Its pointing to same line that i have asked before .
Your previous code doesn't have -a at all, so it's obviously not exactly the same.


test <expression> and [ <expression> ] are equivalent. If <expression> has more than 1 clause then you need to use -a if you want to AND them within the same test.

[[ <expression> ]] is a Korn/bash enhancement which allows some extra operators like && for logical AND.

Quote:
Code:
if test -f ${MGCA_RESULTS_FILE} && test -f ${MGCA_TMP_LOG}

What you're doing here is using the shell's logical AND rather than the test command's logical AND. Which is fine, but it's probably helpful to understand the difference.
# 10  
Old 11-06-2013
Thanks vbe.Its all about working with different companies , so have to change my flavor of UNIX as well.

---------- Post updated 11-06-13 at 12:54 AM ---------- Previous update was 11-05-13 at 10:23 PM ----------

Carlo ,

Thanks for ur comment and good explanation .

When u say test <expression> and [ <expression> ] are equivalent , then why it does not work for ?

I have tried all possible ways but only above with test command and shell's logical AND worked fine.
Even test command with test command's logical AND also didnt work.

Looks bit wired but true Smilie

Thanks,
Himanshu Sood
# 11  
Old 11-06-2013
Quote:
Originally Posted by HIMANSHU SOOD
I have tried all possible ways but only above with test command and shell's logical AND worked fine.
Even test command with test command's logical AND also didnt work.
Without seeing your code, it's impossible to say.
# 12  
Old 11-06-2013
I would try this:
Code:
if [ -s "${MGCA_RESULTS_PATH:-nofile}" -a -s "${MGCA_TMP_LOG:-nofile}" ]

If the variables are null or unset the string "nofile" will be substituted instead. The quotes are there to wrap up any spaces, carriage returns, linefeeds or other characters special to the shell which may be causing your problems.

Andrew
# 13  
Old 11-06-2013
As I already told you it depends of your shell and the syntax, you are confusing 2 syntaxes!

Code:
  
if [  -s $1 -a  -s $2  ] # or
if [  -s ${1} -a  -s ${2} ]  # are identical to or if you prefer:
if [ -s ${MGCA_RESULTS_PATH} -a -s ${MGCA_TMP_LOG} ] # OR
if [ -s  "$MGCA_RESULTS_PATH" -a -s  "$MGCA_TMP_LOG" ]  # OR
if [ -s $MGCA_RESULTS_PATH -a -s $MGCA_TMP_LOG ]     # are identical to
if test -f ${MGCA_RESULTS_FILE} && test -f ${MGCA_TMP_LOG}
# NOT!
if [ -s ${MGCA_RESULTS_PATH} && -s ${MGCA_TMP_LOG} ]

 test "$1" -a "$2"   # should be written as:
    test "$1" && test "$2"

see:
Quote:
APPLICATION USAGE

The XSI extensions specifying the -a and -o binary primaries and the '(' and ')' operators have been marked obsolescent. (Many expressions using them are ambiguously defined by the grammar depending on the specific expressions being evaluated.) Scripts using these expressions should be converted to the forms given below. Even though many implementations will continue to support these obsolescent forms, scripts should be extremely careful when dealing with user-supplied input that could be confused with these and other primaries and operators. Unless the application developer knows all the cases that produce input to the script, invocations like:

test "$1" -a "$2"

should be written as:

test "$1" && test "$2"

to avoid problems if a user supplied values such as $1 set to '!' and $2 set to the null string. That is, in cases where maximal portability is of concern, replace:

test expr1 -a expr2

with:

test expr1 && test expr2

and replace:

test expr1 -o expr2

with:

test expr1 || test expr2

but note that, in test, -a has higher precedence than -o while "&&" and "||" have equal precedence in the shell.

Parentheses or braces can be used in the shell command language to effect grouping.

Parentheses must be escaped when using sh; for example:

test \( expr1 -a expr2 \) -o expr3

This command is not always portable even on XSI-conformant systems depending on the expressions specified by expr1, expr2, and expr3. The following form can be used instead:

( test expr1 && test expr2 ) || test expr3

The two commands:

test "$1"
test ! "$1"

could not be used reliably on some historical systems. Unexpected results would occur if such a string expression were used and $1 expanded to '!', '(', or a known unary primary. Better constructs are:

test -n "$1"
test -z "$1"

respectively.

Historical systems have also been unreliable given the common construct:

test "$response" = "expected string"

One of the following is a more reliable form:

test "X$response" = "Xexpected string"
test "expected string" = "$response"
You should read all of it:
http://pubs.opengroup.org/onlinepubs...#tag_20_128_18
This User Gave Thanks to vbe For This Post:
CarloM
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