Trouble setting variable in a bash script

Question

I am having trouble with a very simple bash script (test.sh):

if [ $# >=1 ]
then
  backup_file=$1
else
  backup_file=~/standard.tar.bz2
fi

echo $backup_file

If I pass an argument:

test.sh myfile

I get the expected output: myfile

Otherwise, I get no output. I am expecting to see (when test.sh is executed with no arguments): ~/standard.tar.bz2

What am I doing wrong?

Feel free to take advantage of the resources listed on the tag wiki, such as shellcheck which automatically diagnoses things like this. — that other guy
– that other guy, Commented Feb 25, 2014 at 21:22

chepner · Accepted Answer · 2014-02-25 20:56:52Z

4

This condition evaluation is the problem:

[ $# >=1 ]

Change this to:

[ $# -ge 1 ]

OR else in BASH:

[[ $# -ge 1 ]]

OR:

(( $# ))

[...] and [[...]] don't allow >= as an operator
You need a space after operators.

edited Feb 25, 2014 at 20:56

chepner

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answered Feb 25, 2014 at 20:50

anubhava

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1 Comment

kojiro Over a year ago

or (( $# )), or [ -n "$1" ]. The last is slightly different, but may be more valuable in some context.

devnull · Accepted Answer · 2014-02-25 20:53:33Z

3

If you're using mathematical operators, use it in the correct context. Instead of saying:

if [ $# >=1 ]

say

if (( $# >=1 ))

(And you don't have to worry about spaces around the operators, or lack thereof.)

answered Feb 25, 2014 at 20:53

devnull

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Comments

kojiro · Accepted Answer · 2014-02-25 20:56:59Z

3

Others have addressed the immediate syntactical problem, but a completely different way to write this would be to take advantage of parameter expansion to use a default value:

backup_file="${1:-$HOME/standard.tar.bz2}"

This will replace backup_file with the value in $1 if and only if it exists.

answered Feb 25, 2014 at 20:56

kojiro

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2 Comments

chepner Over a year ago

You can still use ~ instead of $HOME for the default value.

kojiro Over a year ago

@chepner right, but I actually prefer HOME in scripts, because ~ does some other expansions that are probably not desirable (even if they're unlikely to happen by accident). To each his own. (stackoverflow.com/questions/5930671/…)

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