Remove everything after a changing string [duplicate] - regex

Question

This question already has an answer here:
How to get first N parts of a path?
(1 answer)
Closed 2 years ago.
I'm having some trouble with the following problem;
As input, I get a few lines of paths to files as follows:
root/child/abc/somefile.txt
root/child/def/123/somefile.txt
root/child/ghijklm/somefile.txt
The root/child piece is always in the path, everything after can differ.
I would like to remove everything after the grandchild folder. So the output would be:
root/child/abc/
root/child/def/
root/child/ghijklm/
I've tried the following:
sed 's/\/child\/.*/\/child\/.*/'
But of course that would just give the following output:
root/child/.*
root/child/.*
root/child/.*
Any help would be appreciated!

Answer 1

with cut:
cut -d\/ -f1,2,3 file

Answer 2

With awk: Could you please try following, written and tested with shown samples in GNU awk.
awk 'match($0,/root\/child\/[^/]*/){print substr($0,RSTART,RLENGTH)}' Input_file
Explanation: Adding detailed explanation for above.
awk ' ##Starting awk program from here.
match($0,/root\/child\/[^/]*/){ ##Using match function to match root/child/... till next / in current line.
print substr($0,RSTART,RLENGTH) ##printig substring from RSTART to till RLENGTH.
}
' Input_file ##Mentioning Input_file name here.
With sed:
sed 's/.*\(root\/child\/[^/]*\).*/\1/' Input_file
Explanation: Using sed's substitution method to match root/child/ till next occurrence of / and saving it into temp buffer(back reference method) and substituting whole line with only matched back referenced value.

Answer 3

This might work for you (GNU sed):
sed -E 's/^(([^/]*[/]){3}).*/\1/' file
Delete everything after the third group of non-forward-slashes/slash.

Answer 4

You were close.
sed 's%\(/child/[^/]*\)/.*%\1%'
The regex [^/]* matches as many characters as possible which are not a slash; then we replace the entire match with just the part we captured in parentheses, effectively trimming off the rest.

Answer 5

With Perl:
perl -pe 's{ ^ ( ( [^/]+ / ){3} ) .* $ }{$1}x' in_file > out_file
The Perl one-liner uses these command line flags:
-e : Tells Perl to look for code in-line, instead of in a file.
-p : Loop over the input one line at a time, assigning it to $_ by default. Add print $_ after each loop iteration.
The regex uses this modifier:
x : Disregard whitespace and comments, for readability.
The substitution statement, explained:
^ : beginning of the line.
$ : end of the line.
[^/]+ / : one or more characters that are not slashes (/), followed by a slash.
( [^/]+ / ){3} : one or more non-slash characters, followed by a slash, repeated exactly 3 times.
( ( [^/]+ / ){3} ) : the above, with parenthesis to capture the matched part into the first capture variable, $1, to be used later in the substitution. Capture groups are counted left to right.
.* : zero or more occurrences of any character.
s{THIS}{THAT} : replace THIS with THAT.
SEE ALSO:
perldoc perlrun: how to execute the Perl interpreter: command line switches
perldoc perlre: Perl regular expressions (regexes)
perldoc perlre: Perl regular expressions (regexes): Quantifiers; Character Classes and other Special Escapes; Assertions; Capture groups
perldoc perlrequick: Perl regular expressions quick start