sed match only first expression - bash

Question

I'm doing a parser for build outputs, and I'd like to highlight different patterns in different colors. So for example, I'd like to do:
sed -e "s|\(Error=errcode1\)|<red>\1<_red>|" \
-e "s|\(Error=errcode2\)|<orange>\1<_orange>|" \
-e "s|\(Error=.*\)|<blue>\1<_blue>|"
(so it higlights errcode1 in red, errcode2 in orange, and anything else in blue). The problem with this is that Error=errcode1 matches both the first and the third expression, which will result in <red><blue>Error=errcode1<_red><_blue>... Is there any way to tell sed to match only the first expression, and if it does, do not try the following expressions?
Note, the sed command will actually be auto-generated from files which will be very volatile, so I'd like a generic solution where I don't have to police whether patterns conflict...

Answer 1

Let's start with a simpler example to illustrate the problem. In the code below, both substitutions are performed:
$ echo 'error' | sed 's/error/error2/; s/error/error3/'
error32
If we want to skip the second if the first succeeded, we can use the "test" command which branches if the previous substitution was successful. If we provide no label after t, it branches to the end, skipping all remaining commands:
$ echo 'error' | sed 's/error/error2/; t; s/error/error3/'
error2
Summary
If you want to stop after the first substitution that succeeds, place a t command after each substitution command.
More complex case
Suppose that we want to skip the second but not the third substitution if the first succeeds. In that case, we need to supply a label to the t command:
$ echo 'error' | sed 's/error/error2/; ta; s/error/error3/; :a; s/error/error4/'
error42
In the above, :a defines label a. The command ta branches to label a if the preceeding s command succeeds.
Compatibility
The above code was tested in GNU sed. I am told that BSD sed does not accept ; as a command separator after a label. Thus, on BSD/macOS, try:
echo 'error' | sed -e 's/error/error2/' -e ta -e 's/error/error3/' -e :a -e 's/error/error4/'

Answer 2

You can apply boolean logic to matches with |, & and !.
Solution
(not sure if the syntax is compatible with your system so you may need to add more backslashes)
"s|\(Error=\(.*&!errcode1&!errcode2\)\)|<blue>\1<_blue>|"
Other notes
sed can use any character as a delimiter, so all of the following expressions are equivalent:
"s/foo/bar/"
"s:foo:bar:"
"s|foo|bar|"
"s#foo#bar#"
Also, if you are using bash on a Unix-based system, you can use shell variables if you're running this from a script (since your patterns are enclosed with " and not ', there's a difference).
PREFIX="Error="
TARGET_1="errorcode1"
TARGET_2="errorcode2"
SUB_1="<red>\1<_red>"
SUB_2="<orange>\1<_orange>"
SUB_3="<blue>\1<_blue>"
sed -e "s|\($PREFIX$TARGET_1\)|$SUB_1|" \
-e "s|\($PREFIX$TARGET_2\)|$SUB_2|" \
-e "s|\($PREFIX\(.*&!$TARGET_1&!$TARGET_2\)\)|$SUB_3|" \

Answer 3

If the other errorcodes follow the naming scheme errcodeN, you can negate the 1,2:
sed -e "s|\(Error=errcode1\)|<red>\1<_red>|" \
-e "s|\(Error=errcode2\)|<orange>\1<_orange>|" \
-e "s|\(Error=errcode[^12]\)|<blue>\1<_blue>|"
If the codes exceed number 9: [^12]+

Answer 4

This is not a good application for sed, you should use awk instead. You didn't provide any sample input/output to test against so this is obviously untested but you'd do something like this:
awk '
BEGIN {
colors["errorcode1"] = "red"
colors["errorcode2"] = "orange"
colors["default"] = "blue"
}
match($0,/(.*Error=)([[:alnum:]]+)(.*)/,a) {
code = a[2]
color = (code in colors ? colors[code] : colors["default"])
$0 = sprintf("%s<%s>%s<_%s>%s", a[1], color, code, color, a[3])
}
{ print }
'
The above uses GNU awk for the 3rd arg to match(), it's a minor tweak for other awks.