Parameter checking in scripts

[PJJ]

Hi,
I need to write a script which performes some action on files which are 4 weeks old (no parameters specified), unless another timeframe is specified (in parameter $1).
I can't figure out how to check if $1 is specified or not.
Any help appreciated.
Pete.

[Peter Godron]

Pete,
you could use the length of $1:
a=`expr length "$1"`
or
if [ -z "$1" ]

[Hemmetter]

Hi Peter

see:
man ksh(1) Section "Parameter Substitution."

<...>
${parameter:=word} If parameter is not set or is null, set it to
word; then substitute the value of the
parameter. Positional parameters cannot be
assigned in this way.
<...>
my be what you're searching for.



rgds
HGH

[James R. Ferguson]

Hi Pete:

One way is simply to check the number of arguments passed to the script:

# cat .mysh
#!/usr/bin/sh
if [ $# -eq 0 ]; then
echo "nothing passed"
else
echo "I passed $@"
fi

# ./mysh 123
I passed 123

# ./mysh
nothing passed

Regards!

...JRF...

[Peter Nikitka]

Hi,

set your script variable conditionally:

...
timespec=${1:-28}
...
find .. -mtime +$timespec ...

mfG Peter

[PJJ]

Thanks all for the quick replies.
James's solution seems elegant. But when I run this script with parameters it gives correct output. Running a 2nd time without parameters it gives the same output as the 1st run.
Somehow it seems to conserve the parameters???

[PJJ]

Sorry, I shpuld have supplied output:
$ . script.sh a b c
I passed a b c
$ . script.sh
I passed a b c

[James R. Ferguson]

Hi (again) Pete:

Well, that's quite impossible for the script to retain state between executions. I suspect that your terminal settings are to blame. I suspect that you ran the script with arguments; recalled the command line; and "backspaced" over the arguments. If the backspace truly didn't erase, then you would see the behavior you did.

Regards!

...JRF...

[PJJ]

Hi James,

I didn't recall... Is it the way I call the script?
$ ./script.sh
nothing passed
$ ./script.sh a b c
I passed a b c
$ ./script.sh
nothing passed
$ . script.sh
I passed a b c
$ . script.sh d e f
I passed d e f
$ . script.sh
I passed d e f

This last run not recalled!

[Hein van den Heuvel]

Peter,

Yes your are 'sourcing' the script instead of simply running it.
Is that deliberate? (why?)
What shell are you in while executing this?
Did you use the exact script as provided, or did you already augment it?
This does not reproduce for me.

From the Posix shell man page:
"The dot (.) special command, as in . file, reads the entire file before any commands are executed. Therefore, alias and unalias commands in the file will not apply to any functions defined in the file."


Groetjes,
Hein.