regular expression: put $ in [ ]

Question

echo \"tests\"|perl -pe \"s/s[t$]//g\"
Unmatched [ in regex; marked by <-- HERE in m/s[ <-- HERE 5.020000/ at -e line 1, <> line 1.

Can\'t

Answer 1

Notice the regular expression in the error message (after removing the marker):

m/s[5.020000/

This gives us a clue about what is happening. The $] was replaced with 5.020000 before the regex was evaluated. Referring to man perlvar, we can see that $] is a special variable:

The version + patchlevel / 1000 of the Perl interpreter.

To prevent the variable expansion, add some escaping:

echo "tests" | perl -pe 's/t[s\$]//g'

This will remove ts or literal t$. If you want the $ to represent the end of the line (to trim both test and tests), use:

echo -e "tests\ntest" | perl -pe 's/t(s|$)//g'

or make the s optional:

echo -e "tests\ntest" | perl -pe 's/ts?$//g'

Answer 2

Alternatively, use sed with your expression as is:

echo "tests"| sed "s/s[t$]//g"

Answer 3

You have to escape the $ sign, because it is a special character:

echo "tests"|perl -pe "s/s[t\\$]//g"