Not understanding basic Bash variables and command grouping

Question

Adding in comments to ask specific questions as I go:

Single or double quote marks when settings strings?

echo "Starting..."

Do I need to terminate the line with a ;?

TARGET_DIR="~/Downloads"

I can't get the $TARGET_DIR to expand, tried quotes, preens with $etc, is there a canonical beginners guide to these types of issues that presents them in the proper way, not the force it to work with back tics and multiple lines?

LAST_DOWNLOADED_FILE=$(ls -t $TARGET_DIR | head -n1)
echo "Your newest file in $TARGET_DIR is: $LAST_DOWNLOADED_FILE"

When run on Mac, I get:

ls: ~/Downloads: No such file or directory
Your newest file in ~/Downloads is:

Trying as a one liner:

me@compy $FOO="~/Downloads"; echo $(FOO); ls -t $FOO | head -n1
-bash: FOO: command not found

tldp.org/LDP/Bash-Beginners-Guide/html/… also man command provides useful information — Suvarna Pattayil
– Suvarna Pattayil, Commented Mar 9, 2014 at 6:27

anubhava · Accepted Answer · 2014-03-09 06:38:12Z

4

You need:

TARGET_DIR=~/Downloads

i.e. keep tilde ~/ outside quote, otherwise shell won't expand it and ~ will be treated literally.

edited Mar 9, 2014 at 6:38

answered Mar 9, 2014 at 6:26

anubhava

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5 Comments

ruakh Over a year ago

+1. Note that TARGET_DIR=~/"Downloads" and TARGET_DIR=~/'Downloads' also work. (Not needed for this example, but useful if the stuff after the ~/ is more complicated.)

ruakh Over a year ago

No, the whole ~/ part needs to be outside the quotes.

anubhava Over a year ago

Yes I misspoke, you're right it should be ~/ outside quotes.

Scott Over a year ago

Thanks! What is the proper way to deal with variables that have spaces in their names, or may: echo "Your newest file in $SOME_FILE"; say that $SOME_FILE is 'this is a test'

anubhava Over a year ago

@Scott: You can do TARGETDIR=~/"$SOME_FILE"

Community · Accepted Answer · 2017-05-23 12:20:59Z

0

~ sign inside quotes is considered a literal by shell. You need to either keep it outside of quotes as anubhava suggested in his answer or use eval to interpolate it.

$ TARGET_DIR="~/tmp"
$ echo $TARGET_DIR
~/tmp
$ eval echo $TARGET_DIR
/home/jaypalsingh/tmp

Note: Make sure you read all the pros and cons of eval before considering it as an option.

edited May 23, 2017 at 12:20

CommunityBot

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answered Mar 9, 2014 at 7:23

jaypal singh

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