What does "-?" mean in bash script

Question

I have this script I am looking at, learning scripting but I cannot figure out what this line means:

if [[ $1 = "-?" ]]

I understand the $1 is first argument, but the after the equals I cannot figure it out the -?.h

if [[ $1 = "-?" ]]
    then
    echo "Use is: 235.sh <username>"
    exit 1

The question-mark after the hyphen means it is questionable the hyphen will be there. Also see [What is the meaning of a question mark in bash variable parameter expansion as in ${var?}?](https://stackoverflow.com/q/8889302/608639) — jww, Feb 08 '18 at 02:52
https://stackoverflow.com/questions/17420994/bash-regex-match-string for regular expression in if statement, usually string comparisons take single square braket! http://tldp.org/LDP/abs/html/comparison-ops.html — Allan, Feb 08 '18 at 03:09
Possible duplicate of [What is the meaning of a question mark in bash variable parameter expansion as in ${var?}?](https://stackoverflow.com/questions/8889302/what-is-the-meaning-of-a-question-mark-in-bash-variable-parameter-expansion-as-i) — codeforester, Oct 17 '18 at 18:49

score 5 · Answer 1 · answered Feb 08 '18 at 02:52

5

I think it would be checking to see if the first argument is a string equal to -?

answered Feb 08 '18 at 02:52

Brayden Borneman

score 0 · Answer 2 · 2018-02-08T02:59:19.963

0

You can check this by running:

# [[ "a" = "-?" ]] && echo true
# [[ "-a" = "-?" ]] && echo true
# [[ "a-?" = "-?" ]] && echo true
# [[ "-?" = "-?" ]] && echo true
true

I would guess that is comparing something to the string "-?".

edited Feb 08 '18 at 02:59

answered Feb 08 '18 at 02:50

1

Is the something the $1, or the argument? You should also be careful about globbing when running this check. – Feb 08 '18 at 03:04
This is correct. The canonical flag now is `--help`, but `-?` used to be the standard and is still commonly seen. – that other guy Feb 08 '18 at 03:07

2 Answers2