Question

Given this Bash code:

TEMP="1_2"
echo ${TEMP/_.*/}

why does it print out 1_2 instead of 1?

I’ve also tried these, but they don’t work:

echo ${TEMP/_\.*/}
echo ${TEMP/_\\.*/}

This does work:

echo ${TEMP/_[0-9]*/}

but I want to know:

1. Why isn’t the period acting as a wildcard?
2. What should I use instead?

Answer 1

A question mark is the single-character wildcard. However, it doesn’t work like regular expressions where the asterisk is a quantifier. In Bash, in parameter expansions, an asterisk is a multicharacter wildcard.

$ temp=1_2
$ echo "${temp/_*}"
1

The following also work in this particular situation. See Parameter Expansion in man bash for more information regarding the differences.

echo "${temp%_*}"
echo "${temp%%_*}"

I recommend against using all-caps variable names in order to reduce the chance of name collision with shell or environment variables.