Ubuntu – Compare 2 numerals and copy only similar part sed/grep/awk

bashscripts

Supposing I have a array called a. There are 2 entries in a array a[1] and a[2].So each element contains a numeral value. Both these values have a similar starting numbers however they have different endings. I am to copy the similar part and ignore the rest.

So as an example

$ echo ${a[1]}
.1.3.6.1.4.1.232.13600256

$ echo ${a[2]}
.1.3.6.1.4.1.232.13600276

I need some command to compare these elements and then copy only the similar part until the first non matching field.
ie., in this example

OUTPUT

similar part is .1.3.6.1.4.1.232

Another example

$ echo ${a[1]}
.1.3.6.1.4.1.759.2344.454545

$ echo ${a[2]}
.1.3.6.1.4.1.759.3234.454545

OUTPUT for this example

similar part is .1.3.6.1.4.1.759

Best Answer

From Stack Overflow:

In sed, assuming the strings don't contain any newline characters:
string1="test toast"
string2="test test"
printf "%s\n%s\n" "$string1" "$string2" | sed -e 'N;s/^$.*$.*\n\1.*$/\1/'

This assumes that the strings themselves don't contain newlines.

Therefore you can do:

printf "%s\n" "${a[1]}" "${a[2]}" | sed -r 'N;s/^(.*)(\..*)?\n\1.*$/\1/'

The (\..*) should eliminate a trailing . from the common section.

The solution involves two parts:

Getting sed to work across two lines. This is done using N, and can be avoided if a character is guaranteed to be not in the input. For example, because spaces are not present in the elements as given, we can instead use:
```
printf "%s " "${a[1]}" "${a[2]}" | sed -r 's/^(.*)(\..*)? \1.*$/\1/'
```
Essentially, the character or string separating the two elements in the output should be used after %s in the printf formatting string, and before \1 in the regular expression.
Finding a repeating string using regex. The trick for this is well-known, and is always a variation of:
```
(.*)\1
```
.* matches any set of characters, and () groups them for later reference, by \1. Thus (.*)\1 is any sequence of characters followed by itself.

Related Solutions

Ubuntu – Add particular strings to an array sed/awk/grep

Using grep:

mapfile -t var < <(grep -Po '^\s+\K[^ ]+(?= ?\(\d+\),?$)' file.txt)

grep -P will use PCRE (Perl Compatible Regular Expression)
grep -o will print the matched portion of the line
^\s+\K will match the lines starting with whitespaces and \K will discard the match
[^ ]+ will match our desired portion
(?= *$\d+$) is the zero width positive look ahead pattern ensuring zero or one space followed by (, one or more digits, ) and zero or one , at the end after our desired match

mapfile is a shell built-in, used to create array.

$ mapfile -t var < <(grep -Po '^\s+\K[^ ]+(?= ?\(\d+\),?$)' file.txt)

$ echo "${var[0]}"
copyOperationPending

$ echo "${var[1]}"
copyInProgress

$ echo "${#var[@]}"
19

Ubuntu – Extract word from string using grep/sed/awk

You can use grep with PCRE (-P):

grep -Po 'spring.profiles.active=\K[^ ]+' <<<'.....string.....'

spring.profiles.active= will match this substring literally, \K will discard the match
[^ ]+ will select the desired portion i.e. the portion after spring.profiles.active=, till the next space

For a file:

grep -Po 'spring.profiles.active=\K[^ ]+' file.txt

Example:

% grep -Po 'spring.profiles.active=\K[^ ]+' <<<'00:28:04 /usr/lib/jvm/jre/bin/java -DJDBC_CONNECTION_STRING= -Dspring.profiles.active=qa -XX:MaxPermSize=256'
qa

sed would take similar logic:

sed -r 's/.*spring.profiles.active=([^ ]+).*/\1/' <<<'.....string.....'

Example:

% sed -r 's/.*spring.profiles.active=([^ ]+).*/\1/' <<<'00:28:04 /usr/lib/jvm/jre/bin/java -DJDBC_CONNECTION_STRING= -Dspring.profiles.active=qa -XX:MaxPermSize=256'
qa

Handling errors:

In your script you may want to handle the case where there is no match, in other words where your original string does not contain spring.profiles.active=. In the above sed example, you obtain the whole original string, which could create problems:

% var="$(sed -r 's/.*spring.profiles.active=([^ ]+).*/\1/' <<<'00:28:04 /usr/lib/jvm/jre/bin/java -DJDBC_CONNECTION_STRING= -XX:MaxPermSize=256')"
% echo $var
00:28:04 /usr/lib/jvm/jre/bin/java -DJDBC_CONNECTION_STRING= -XX:MaxPermSize=256

If you prefer to obtain the empty string when there is no match, add the -n option to the sed command and the p option to the sed s command, like this:

% var="$(sed -rn 's/.*spring.profiles.active=([^ ]+).*/\1/p' <<<'00:28:04 /usr/lib/jvm/jre/bin/java -DJDBC_CONNECTION_STRING= -XX:MaxPermSize=256')"
% echo $var

% var="$(sed -rn 's/.*spring.profiles.active=([^ ]+).*/\1/p' <<<'00:28:04 /usr/lib/jvm/jre/bin/java -DJDBC_CONNECTION_STRING= -Dspring.profiles.active=qa -XX:MaxPermSize=256')"
% echo $var
qa

Then you can test if $var is empty or not.