I need to search a string for a substring, if the substring is found print the string upto the end of the substring.i.e

str="this is a long string"
substring="long"
expected="this is a long"

I have tried bash string manipulation and failed. Tried to use an awk command, but I can't get it right. This works if substring is not in a variable, but I require it in a variable since the input varies.

awk -F'long' '{print $1}' <<<$str

awk -v myvar="$substring"  -F'myvar' '{print $1}' <<<$str

prints the whole string. Any help will be appreciated.

CodePudding user response：

If you looked for bash only solution, one of the options would be:

sfx="${str#*${substring}}"
expected="${str%"${sfx}"}"

Which uses prefix removal (of anything $substring) to determine the trailing part. And then uses suffix removal to trim that from $str yielding your expected value.

Since you seem to be OK with answers beyond just shell (like using awk), here's similar with sed:

echo "$str" | sed -e 's#^\(.*'"${substring}"'\).*#\1#'

-> match the whole line with anything up to and including $substring being saved in the first group and replace that line with content of the first matched group.

note: both of these examples are not greedy and will match up to the first $substring.