I'm trying to control error output of a command parametrically but piping command is handled as another parameter. Test scripts below;
...$ cat printOutput.sh
#!/bin/sh
if [ $# -gt 0 ]; then echo "Wrong parameter $1"; exit; fi
echo "stdout"
echo "errout" >&2
...$ cat test.sh
#!/bin/sh
cmdBase="./printOutput.sh"
if [ -z $1 ]; then
#Do not pipe
cmd="$cmdBase"
else
#Pipe err
cmd="$cmdBase 2>/dev/null"
fi
echo "`$cmd`"
Error output should only print when --verbose option is selected but it prints anyways.Test script shows that 2>/dev/null piping is handled as a parameter.
...$ ./test.sh --verbose
Wrong parameter 2>/dev/null
...$ sh -x ./test.sh --verbose
+ cmdBase=./printOutput.sh
+ [ -z --verbose ]
+ cmd=./printOutput.sh 2>/dev/null
+ ./printOutput.sh 2>/dev/null
+ echo Wrong parameter 2>/dev/null
Wrong parameter 2>/dev/null
Why/How is the piping handled as an argument here?
It appears to me that output redirection is handled before the variable expansion.
The most obvious way is to handle this within your if statement:
#!/bin/sh
cmdBase="./printOutput.sh"
if [ -z $1 ]; then
#Do not pipe
cmdOut="`$cmdBase`"
else
#Pipe err
cmdOut="`$cmdBase 2>/dev/null`"
fi
echo "$cmdOut"