Construct file path using shell parameter expansion

Question

I need to construct an absolute file path based on the values of two variables in bash. I have the following two variables:

MY_FILE_NAME=myfile-1.0.0.80234.txt ### This variable is NOT guaranteed to be set
WORKING_DIR=/var/my_working_dir     ### This variable is guaranteed to be set
MY_PATH=<Some parameter expansion magic>

If the variable MY_FILE_NAME is set then MY_PATH should have the value:

/var/my_working_dir/myfile-1.0.0.80234.txt

If the variable MY_FILE_NAME is not set then MY_PATH should be same as value of WORKING_DIR. How do I achieve this using parameter expansion preferably in just one line.

If you don't mind a trailing / then simple MY_PATH="$WORKING_DIR/$MY_FILE_NAME" will also work — anubhava
– anubhava, Commented Oct 14, 2013 at 18:04

anubhava · Accepted Answer · 2013-10-14 18:09:31Z

2

Following should work for you:

[[ $MY_FILE_NAME ]] && MY_PATH="$WORKING_DIR/$MY_FILE_NAME" || MY_PATH="$WORKING_DIR"

answered Oct 14, 2013 at 18:09

anubhava

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2 Comments

The Governor Over a year ago

Thanks! This worked. I realized I posted a stupid question when I first saw your comment. It's fine if extra trailing slashes get added.

anubhava Over a year ago

Ah in that case you just needed MY_PATH="$WORKING_DIR/$MY_FILE_NAME"

michael501 · Accepted Answer · 2013-10-14 20:13:52Z

2

try this :

MY_PATH=${WORKING_DIR}${MY_FILE_NAME:+/}${MY_FILE_NAME:-}

edited Oct 14, 2013 at 20:13

answered Oct 14, 2013 at 18:52

michael501

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2 Comments

anubhava Over a year ago

This will add an extra / in the end and OP wrote If the variable MY_FILE_NAME is not set then MY_PATH should be same as value of WORKING_DIR.

anubhava Over a year ago

Thanks, I think it be simplified to: MY_PATH=${WORKING_DIR}${MY_FILE_NAME:+/}${MY_FILE_NAME}

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