Replace all occurrences of a character in a variable using korn script

Question

Part of the Korn script I am writing requires that I replace all occurrences of the ' character with two occurrences (''). I am trying to log some SQL that I am generating in this script to a column in another table but single quotes need to be replaced with 2 instances of the single quote character. I know there must be examples of this functionality somewhere but I'm not finding a string replace example specific to variables anywhere.

Answer 1

In ksh93 and zsh, there's a string replacement construct ${VARIABLE//PATTERN/REPLACEMENT}, used twice in the following snippet: once to replace ' by '' and once to replace newlines by '+char(10)+'. If there are no newlines in the input string, you can omit the second assignment command.

quoted_string=\'${raw_string//\'/\'\'}\'
quoted_string=${quoted_string//$'\n'/"'+char(10)+'"}

This construct is also available in bash, but the quoting rules are different. The following snippet works in all of ksh93, bash and zsh.

quoted_string=\'${raw_string//$'\''/$'\'\''}\'
quoted_string=${quoted_string//$'\n'/$'\'+char(10)+\''}

In ksh88 and other shells, you need to write a relatively complex loop to replace the single quotes one at a time. The following snippet doubles single quotes, but leaves newlines unchanged).

q="$raw_string"; quoted_string=
while
    quoted_string="$quoted_string'${q%%\'*}'"
    case "$q" in *\'*) q="${q#*\'}";; *) false;; esac
do :; done

Alternatively, you can use sed. Be careful when feeding the data to sed, as echo doesn't always print its argument as-is.

quoted_string="'$(printf '%s\n' "$raw_string" |
                  sed -n -e "s/'/''/g" -e 'H' \
                      -e '$ g' -e 's/^\n//' -e "s/\\n/'+char(10)+'/g" -e '$ p')'"

If there are no newlines in the string, the following much simpler sed command suffices.

quoted_string="'$(printf '%s\n' "$raw_string" | sed -e "s/'/''/g")'"

Answer 2

Is there any particular reason you couldn't call sed from within your ksh script?

This simple script:

#!/bin/ksh

foo="left ' right"
echo $foo
foo=$(echo "$foo" | sed "s#\'#\'\'#g")
echo $foo

gives me this output:

left ' right
left '' right