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To substitute it with nothing would be the most obvious.

<source grep -Po "^.*?(?=(, characters I don't want)?\$)"

If the text to remove may contain anything including / or regex operators (but not newline characters which wouldn't make sense, nor NUL characters which can be passed in command arguments nor environment variables) and is stored in a shell variable, you do not want to use sed "s/$string\$//" as that would make it a command injection vulnerability.

string='/.*\^$'
<source grep -Po "^.*?(?=(\Q$string)?\$)"
<source pcregrep -o1 "^(.*?)\Q$string\E\$"

Most obvious here would be to use sed:

To substitute that string when found at the end of the line $ which we escape as \$ for the shell (to be future proof in case $/ means something in the shell in the future).

To also remove whatever follows that string if any, replace the \$ with .*, though we'd need to change the locale the C to guarantee .* matches everything up to the end even if that's not valid text in the user's locale:

<source LC_ALL=C sed "s/, characters I don't want.*//"

<source LC_ALL=C grep -Po "^.*?(?=(, characters I don't want)?\$)"

Or to remove everything if any after that string as well:

<source LC_ALL=C grep -Po "^.*?(?=, characters I don't want|\$)"

Or to remove everything if any after that string as well:

<source pcregrep -o1 "^(.*?)(, characters I don't want|\$)"

If the text to remove may contain anything including / or regex operators (but not newline characters which wouldn't make sense, nor NUL characters which can be passed in command arguments nor environment variables) and is stored in a shell variable, you do not want to use sed "s/$string\$//" as that would make it a command injection vulnerability.

string='/.*\^$'
<source LC_ALL=C grep -Po "^.*?(?=(\Q$string)?\$)"
<source pcregrep -o1 "^(.*?)(\Q$string\E)?\$"

Or to remove everything if any after that string as well:

<source LC_ALL=C grep -Po "^.*?(?=\Q$string|\$)"
<source pcregrep -o1 "^(.*?)(\Q$string\E|\$)"

Or to remove everything if any after that string as well:

<source perl -spe 's/\Q$string\E.*$//' -- -string="$string"

perl treats input as bytes not as if encoded in the user's locale charset by default, so we don't need to change the locale there.

sed "s/, characters I don't want\$//"

To substitute it with nothing would be the most obvious.

With GNU grep or compatible, when built with perl-like regexp support, that could be:

grep -Po "^.*?(?=(, characters I don't want)?\$)"

Or with pcregrep (when perl-like regex support is enabled in GNU grep, that's actually via libpcre which comes with pcregrep as an example application though has features beyond those of GNU grep):

pcregrep -o1 "^(.*?)(, characters I don't want)?\$"

<source sed "s/, characters I don't want\$//"

To substitute it with nothing would be the most obvious.

With GNU grep or compatible, when built with perl-like regexp support, that could be:

<source grep -Po "^.*?(?=(, characters I don't want)?\$)"

Or with pcregrep (when perl-like regex support is enabled in GNU grep, that's actually via libpcre which comes with pcregrep as an example application though has features beyond those of GNU grep):

<source pcregrep -o1 "^(.*?)(, characters I don't want)?\$"

If the text to remove may contain anything including / or regex operators (but not newline characters which wouldn't make sense, nor NUL characters which can be passed in command arguments nor environment variables) and is stored in a shell variable, you do not want to use sed "s/$string\$//" as that would make it a command injection vulnerability.

With the perl-grep ones, you can use:

string='/.*\^$'
<source grep -Po "^.*?(?=(\Q$string)?\$)"
<source pcregrep -o1 "^(.*?)\Q$string\E\$"

That still chokes on $strings that contain \E, though not with as dramatic consequences as with sed.

Or you could use perl directly which has a sed mode with its -p option, has mechanisms to pass arbitrary strings (here using -s for a crude option passing, but you could also use @ARGV directly (equivalent of python's sys.argv) or environment variables (mapped to the %ENV associative array)), and can \Quote strings inside regexps (here with \E in $string not being a problem):

<source perl -spe 's/\Q$string\E$//' -- -string="$string"

Note that contrary to sed, the line delimiter is included in the pattern space ($_ in perl on which s/// acts by default) by default and its $ regex operator matches either at the end of the subject or before a line delimiter at the end of the subject so is able to cope with both delimited and undelimited lines.

sed "s/, characters I don't want\$//"

To substitute it with nothing would be the most obvious.

With GNU grep or compatible, when built with perl-like regexp support, that could be:

grep -Po "^.*?(?=(, characters I don't want)?\$)"

sed "s/, characters I don't want\$//"

To substitute it with nothing would be the most obvious.

With GNU grep or compatible, when built with perl-like regexp support, that could be:

grep -Po "^.*?(?=(, characters I don't want)?\$)"

Or with pcregrep (when perl-like regex support is enabled in GNU grep, that's actually via libpcre which comes with pcregrep as an example application though has features beyond those of GNU grep):

pcregrep -o1 "^(.*?)(, characters I don't want)?\$"