Sort input file by the results of a regex

regular expressionsorttext processing

I'd like to sort a file based on the results of a regex expression. For example, if I have the following property declarations in Obj-C

@property (nonatomic, strong) id <AlbumArtDelegate, UITextFieldDelegate> *albumArtView; // 1
@property (nonatomic, strong, readonly) UIImageView *profileView;  // 2
@property (nonatomic, strong, readwrite) UIButton *postFB;          // 3
@property (nonatomic, assign) UIButton *saveButton;      // 4

By default they will sort in order [4, 1, 2, 3], but I would like to sort them in order of the actual property names, [1, 3, 2, 4]. I can write a regular expression to tease out just the property name, is it possible for me to sort by the results of that expression?

Is there any built-in Unix tool that will do this for me? I'm working in Xcode, so VIM/emacs solutions won't help.

Also, the reason I'd like to do this using a regex is so that I can expand my sorting algorithm to work in other situations. Use it to sort method declarations, import statements, etc.

Best Answer

A general method to sort by an arbitrary function of the contents of the line is as follows:

Get the key you want to sort by, and copy it to the beginning of the line
Sort
Delete the key from the beginning of the line

Here is a key you can use in this particular case: this sed program will output the the line from the last identifier to the end.

% sed -e 's/^.*[^[:alnum:]_]\([[:alpha:]][[:alnum:]_]*\)/\1/' < decls

albumArtView; // 1
profileView;  // 2
postFB;          // 3
saveButton;      // 4

To put these keys and the original lines side by side:

% paste <(sed -e 's/^.*[^[:alnum:]_]\([[:alpha:]][[:alnum:]_]*\)/\1/' < decls) decls

To sort them ...

| sort

and to leave just the second field (the original line)

| cut -f 2-

All together (sorting in reverse order, so there's something to show):

% paste <(sed -e 's/^.*[^[:alnum:]_]\([[:alpha:]][[:alnum:]_]*\)/\1/' < decls) decls \
  | sort -r \
  | cut -f 2-

→

@property (nonatomic, assign) UIButton *saveButton;      // 4
@property (nonatomic, strong, readonly) UIImageView *profileView;  // 2
@property (nonatomic, strong, readwrite) UIButton *postFB;          // 3
@property (nonatomic, strong) id <AlbumArtDelegate, UITextFieldDelegate> *albumArtView; // 1

Related Solutions

Sort by regular expressions

The usual sort command doesn't provide an included way to specify your specific "dictionary", and while the grep command allows you to provide a file of regular expressions, it won't change the order of the output. But you can put both together in a simple foreach loop -- here's an example that works in the bash shell:

for i in `cat fileofregexp`; do grep "$i" myinputfile; done

This takes each regexp line from your file of regular expressions one by one, and outputs any match from your inputfile, so the resulting output will be sorted by your regexp order. Note that any lines in your inputfile that don't match at all will not make it to the output.

Addendum: As requested, here's a version using a while loop:

while IFS= read -r i; do grep "$i" myinputfile; done  < fileofregexp

Sort part of a file

I think what you're after is something like these:

Method #1: using head & tail

$ (head -n 2 sample.txt; tail -n +3 sample.txt | sort -t' ' -nk2) > a.tmp && mv a.tmp sample.txt

Nome     Note
------------
Mehdi    0
Shnou    5
Others   10
Sunday   20

This takes the first line of the text file, then tails everything after the first 2 lines which is then sorted.

Method #2: just using head

$ (head -n 2; sort -t' ' -nk2) < sample.txt > a.tmp && mv a.tmp sample.txt

Nome     Note
------------
Mehdi    0
Shnou    5
Others   10
Sunday   20

Takes the text file as input, displays just the first line, sort the rest.

It's typically not a good idea to edit files in place. It's possible, but better to use an intermediate file.

Method #3: Doing #2 without an intermediate file

Stealing the idea from @StephaneChazelas you could do the following using the "1<>" notation to open a file for reading & writing, and the improvements he suggested with the sort command.

$ (head -n 2; sort -nk2) < sample.txt 1<> sample.txt

Nome     Note
------------
Mehdi    0
Shnou    5
Others   10
Sunday   20