Scripting help

[slyth]

I would like to include a validation within a script that displays usage information when an error message is returned by the command:

if <error is returned> then //standard error
echo usage command parameter1 | parameter2
fi

[secondmouse]

slyth,
Usually most errors result in an exit and return a non-zero value, therefore you cannot wait for error to happen. It's better to detect conditions in which error will happen. Say you are writing a script that expects 1 argument, you can do a test if the condition is met before doing anything else:

#/bin/bash
[ $# -eq 1 ] || { echo "usage: `basename $0` para1"; exit 1; }


This script is equivalent to
#/bin/bash
if [ $# -ne 1 ]; then

echo "usage: `basename $0` para1"
exit 1

fi
which is much easier to understand.

[Cabhan]

If you mean how you can run a program and then report an error if the program errors, consider something like this:

if ! some_command; then
    # Error
fi

Virtually every program (I say "virtually", but really, every program) will exit with code 0 if they are successful, and non-zero if there was an error. The above code executes a command, and then if the return code is non-zero, executes the code in the if statement.

[slyth]

The following script doesn't compile somehow, see anything wrong?

What does $# represent?

#/bin/bash
if [$# -eq 1]; then
echo "usage: test arg";
exit 1;
fi

if [$1 -eq "arg"] then
exit 0
fi

./test
[root@localhost bin]# ./test
./test: line 2: [0: command not found
./test: line 9: syntax error near unexpected token `fi'
./test: line 9: `fi'
[root@localhost bin]#

[secondmouse]

should be

#/bin/bash
if [ $# -ne 1 ]; then
echo "usage: test arg"
exit 1;
fi

if [ "$1" == "arg" ]; then
exit 0
fi

Please note the spaces around the conditional expressions.

[slyth]

No luck yet

[secondmouse]

Try to use single '=' instead of double in the string comparison:
if [ "$1" = "arg" ]; then

[GMorris]

##next line, needs a ! in front, hence the line 2 error
#/bin/bash
if [$# -eq 1]; then
echo "usage: test arg";
exit 1;
fi

if [$1 -eq "arg"] then
##next line, try a ; after the 0
exit 0
fi

./test
[root@localhost bin]# ./test
./test: line 2: [0: command not found
./test: line 9: syntax error near unexpected token `fi'
./test: line 9: `fi'
[root@localhost bin]#

As for the brackets, I'm not sure, but I think I found two of the problems anyway!