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Shell Programming and Scripting

Variable explanation

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# 1  
Old 10-06-2009
Variable explanation
What does this part in the following code ?

if [ ".$t" != . ]; then
$t shows some time values for getting the response, but why .$t and what does the . after the !=

Code:
t=$(time -p wget --quiet --post-data='username=xxx&password=xxxx&id=xxxxxx' --no-check-certificate --output-document=/tmp/sms-status_out --timeout=30 "https://www.xxx.de/gsm/status.php" | perl -ne 'print int($1 * 1000) if /^real (\S+)/')
if [ ".$t" != . ]; then

thx

Alex
# 2  
Old 10-06-2009
Hi.

It's one way of showing if $t is set or not.

If t is not set then the statement would expand to

Code:
if [ . != . ]; then

which is false.

If t is set to, say A, then that becomes

Code:
if [ .A != . ]; then

which is true, thus if $t is set, the if statement is executed, otherwise the else part (iif one exists) is.
# 3  
Old 10-06-2009
OK, thx!
# 4  
Old 10-06-2009
Quote:
Originally Posted by locutus01
What does this part in the following code ?

if [ ".$t" != . ]; then
$t shows some time values for getting the response, but why .$t and what does the . after the !=

Code:
t=$(time -p wget --quiet --post-data='username=xxx&password=xxxx&id=xxxxxx' --no-check-certificate --output-document=/tmp/sms-status_out --timeout=30 "https://www.xxx.de/gsm/status.php" | perl -ne 'print int($1 * 1000) if /^real (\S+)/')
if [ ".$t" != . ]; then


It's a workaround for pre-POSIX shells.

It's a convoluted way of doing:

Code:
if [ -n "$t" ]

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