传递给命令行参数时如何在Bash中转义变量

Question

I've got a Bash script (Cygwin) that uses some Windows paths with spaces in them. Consequently, I have escaped the space with a \\ in my variable definition.

Everything within the script works fine. However, I need to pass this variable as an argument to a command-line executable. When I do that, my escaping gets messed up.

Sample non-functional script:

#!/bin/sh

# File paths
destinationPath="/cygdrive/c/Documents and Settings/Eric/My Documents/"
attachments="\n2013-12-12.pdf"
body="Test Body"
recipient="asdf@asdf.com"


# Prepare attachments
args=""
for file in $attachments ; do
    file=${file//[ \\n]/}
    touch $file
    mv $file "$destinationPath/$file"
    args="$args -a $destinationPath/$file"
done


# Send email
echo -e $body | email --from-addr nosender@mydomain.com --from-name "Automated CSS Downloader" --subject "Downloaded new file(s) \
  from CSS" $args eric@mydomain.com

Output from the script:

$ bash -x test.sh
+ destinationPath='/cygdrive/c/Documents and Settings/Eric/My Documents/'
+ attachments='\n2013-12-12.pdf'
+ body='Test Body'
+ recipient=asdf@asdf.com
+ args=
+ for file in '$attachments'
+ file=2013-12-12.pdf
+ touch 2013-12-12.pdf
+ mv 2013-12-12.pdf '/cygdrive/c/Documents and Settings/Eric/My Documents//2013-12-12.pdf'
mv: listing attributes of `2013-12-12.pdf': Invalid argument
+ args=' -a /cygdrive/c/Documents and Settings/Eric/My Documents//2013-12-12.pdf'
+ echo -e Test Body
+ email --from-addr nosender@mydomain.com --from-name 'Automated CSS Downloader' --subject 'Downloaded new file(s) from CSS' -a /cygdrive/c/Documents and Settings/Eric/My Documents//2013-12-12.pdf eric@mydomain.com
email: WARNING: Email address 'and' is invalid. Skipping...
email: FATAL: Could not open attachment: /cygdrive/c/Documents: No such file or directory

So, as you can see, the escaped space in the path is not being exported in the $args variable. I am assuming the error comes on the line "args=...". But I am not sure how to escape $destinationPath to ensure that the escaped characters are retained.

I've tried using double quotes (with no escaped space) in destinationPath, but to no avail. If I try to double quote $destinationPath in the args= line, then the output also gets all screwed up with a bunch of extra quoting.

How can I get this to work? I've tried playing around with the $IFS variable, but I don't really know what I'm doing with it and can't seem to get it working with that either, although I suspect the solution has something to do with $IFS.

Answer 1

There's no good way of doing this without an array. (There's a not good way of doing it, using eval , but the array is simpler.)

The problem is that you want each file to end up as one argument to email , but you want to accumulate all those arguments into a Bash variable. There's just no way to do that: you can cause the Bash variable to be inserted as a single argument ( "$arg" ) or you can cause it to be inserted as however many words it gets split into ( $arg ), but you can't get it to be split according to whether or not spaces were escaped when the variable was created, because Bash only remembers the string assigned to a variable, not the escape marks.

However, you can do it with an array, because you can make every filename exactly one array element, and you can get Bash to insert an array as one argument per element.

Here's how:

# File paths                                                                                                                              
destinationPath="/cygdrive/c/Documents and Settings/Eric/My Documents/"
attachments="\n2013-12-12.pdf"
body="Test Body"
recipient="asdf@asdf.com"


# Prepare attachments                                                                                                             
args=()
for file in $attachments ; do
    file=${file//[ \\n]/}
    touch $file
    mv $file "$destinationPath/$file"
    args+=(-a "$destinationPath/$file")
done

# Send email                                                                                                                      
echo -e $body |
  email --from-addr nosender@mydomain.com \
        --from-name "Automated CSS Downloader" \
        --subject "Downloaded new file(s) from CSS" \
        "${args[@]}" eric@mydomain.com

You might also want to make the attachments variable into an array; from the presence of the newline character, I'm assuming that you're actually setting it in some more complicated way, so I didn't change the code. But your current code won't work if the attachment name has a space in it (and I'm pretty sure that the newline will be eliminated by the parameter expansion in the for form, unless you've altered the value of $IFS , so file=${file//[ \\\\n]/} shouldn't be necessary.)

Answer 2

You need escaped double quoted marks when providing destinationPath in a string.

This should work:

#!/bin/sh                                                                                                                                 

# file paths                                                                                                                              
destinationPath="/cygdrive/c/Documents and Settings/Eric/My Documents/"
attachments="\n2013-12-12.pdf"
body="Test Body"
recipient="asdf@asdf.com"


        # prepare attachments                                                                                                             
        args=""
        for file in $attachments ; do
            file=${file//[ \\n]/}
            touch $file
            mv $file "$destinationPath/$file"
            #HERE YOU NEED ESCAPED DOUBLEQUOTED
            args="$args -a \"$destinationPath/$file\""
        done

        # send email                                                                                                                      
        echo -e $body | email --from-addr nosender@mydomain.com --from-name "Automated CSS Downloader" --subject "Downloaded new file(s) \
from CSS" $args eric@mydomain.com