Question

I have a pattern in a file as follows which can/cannot span over multiple lines :

 abcd25
 ef_gh
 ( fg*_h
 hj_b*
 hj ) {

What I have tried :

perl -nle ‘print while m/^\s*(\w+)\s+(\w+?)\s*(([\w-0-9,* \s]))\s{/gm’

I dont know what the flags mean here but all I did was write a regex for the pattern and insert it in the pattern space .This matches well if the the pattern is in a single line as :

abcd25 ef_gh ( fg*_h hj_b* hj ) {

But fails exclusively in the multiline case !

I started with perl yesterday but the syntax is way too confusing . So , as suggested by one of our fellow SO mate ,I wrote a regex and inserted it in the code provided by him .

I hope a perl monk can help me in this case . Alternative solutions are welcome .

Input file :

 abcd25
 ef_gh
 ( fg*_h
 hj_b*
 hj ) {

 abcd25
 ef_gh
 fg*_h
 hj_b*
 hj ) {

 jhijdsiokdù ()lmolmlxjk;
 abcd25 ef_gh ( fg*_h hj_b* hj ) {

Expected output :

 abcd25
 ef_gh
 ( fg*_h
 hj_b*
 hj ) {
 abcd25 ef_gh ( fg*_h hj_b* hj ) {

The input file can have multiple patterns which coincides with the start and end pattern of the required pattern.
Thanks in advance for the replies.

Answer 1

The regex does not match even the single line. What do you think the double parentheses do?

You probably wanted

m/^\s*(\w+)\s+(\w+?)\s*\([\w0-9,*\s]+\)\s{/gm

Update: The specification has changed. The regex has (almost) not, but you have to change the code slightly:

perl -0777 -nle 'print "$1\n" while m/^\s*(\w+\s+\w+?\s*\([\w0-9,*\s]+\)\s{)/gm'

Another update:

Explanation:

• The switches are described in perlrun: zero, n, l, e

• The regex can be auto-explained by YAPE::Regex::Explain

  perl -MYAPE::Regex::Explain -e 'print YAPE::Regex::Explain->new(qr/^\s*(\w+\s+\w+?\s*\([\w0-9,*\s]+\)\s{)/)->explain'
  The regular expression:
  
  (?-imsx:^\s*(\w+\s+\w+?\s*\([\w0-9,*\s]+\)\s{))
  
  matches as follows:
  
  NODE                     EXPLANATION
  ----------------------------------------------------------------------
  (?-imsx:                 group, but do not capture (case-sensitive)
                           (with ^ and $ matching normally) (with . not
                           matching \n) (matching whitespace and #
                           normally):
  ----------------------------------------------------------------------
    ^                        the beginning of the string
  ----------------------------------------------------------------------
    \s*                      whitespace (\n, \r, \t, \f, and " ") (0 or
                             more times (matching the most amount
                             possible))
  ----------------------------------------------------------------------
    (                        group and capture to \1:
  ----------------------------------------------------------------------
      \w+                      word characters (a-z, A-Z, 0-9, _) (1 or
                               more times (matching the most amount
                               possible))
  ----------------------------------------------------------------------
      \s+                      whitespace (\n, \r, \t, \f, and " ") (1
                               or more times (matching the most amount
                               possible))
  ----------------------------------------------------------------------
      \w+?                     word characters (a-z, A-Z, 0-9, _) (1 or
                               more times (matching the least amount
                               possible))
  ----------------------------------------------------------------------
      \s*                      whitespace (\n, \r, \t, \f, and " ") (0
                               or more times (matching the most amount
                               possible))
  ----------------------------------------------------------------------
      \(                       '('
  ----------------------------------------------------------------------
      [\w0-9,*\s]+             any character of: word characters (a-z,
                               A-Z, 0-9, _), '0' to '9', ',', '*',
                               whitespace (\n, \r, \t, \f, and " ") (1
                               or more times (matching the most amount
                               possible))
  ----------------------------------------------------------------------
      \)                       ')'
  ----------------------------------------------------------------------
      \s                       whitespace (\n, \r, \t, \f, and " ")
  ----------------------------------------------------------------------
      {                        '{'
  ----------------------------------------------------------------------
    )                        end of \1
  ----------------------------------------------------------------------
  )                        end of grouping
  ----------------------------------------------------------------------
  

  • The /gm switches are explained in perlre