mkdir error in bash script

问题

The following is a fragment of a bash script that I'm running under cygwin on Windows:

deployDir=/cygdrive/c/Temp/deploy

timestamp=`date +%Y-%m-%d_%H:%M:%S`
deployDir=${deployDir}/$timestamp

if [ ! -d "$deployDir" ]; then
    echo "making dir $deployDir"
    mkdir -p $deployDir
fi

This produces output such as:

making dir /cygdrive/c/Temp/deploy/2010-04-30_11:47:58
mkdir: missing operand
Try `mkdir --help' for more information.

However, if I type /cygdrive/c/Temp/deploy/2010-04-30_11:47:58 on the command-line it succeeds, why does the same command not work in the script?

Thanks, Don

回答1:

Change:

mkdir -p $deploydir

mkdir -p "$deployDir"

Like most Unix shells (maybe even all of them), Bourne (Again) Shell (sh/bash) is case-sensitive. The dir var is called deployDir (mixed-case) everywhere except for the mkdir command, where it is called deploydir (all lowercase). Since deploydir (all lowercase) is a considered distinct variable from deployDir (mixed-case) and deplydir (all lowercase) has never had a value assigned to it, the value of deploydir (all lowercase) is empty string ("").

Without the quotes (mkdir $deploydir), the line effectively becomes mkdir (just the command without the required operand), thus the error mkdir: missing operand.

With the quotes (mkdir "$deploydir"), the line effectively becomes mkdir "" (the command to make a directory with the illegal directory name of empty string), thus the error mkdir: cannot create directory'.

Using the form with quotes (mkdir "$deployDir") is recommended in case the target directory name includes spaces.