demo_regsub.f90 Source File

     program demo_regsub
     use M_regex, only: regex_type, regcomp, regexec, regerror, regmatch, regfree, regsub
     implicit none
     type(regex_type)             :: regex
     integer,parameter            :: maxmatch=10
     integer                      :: matches(2,maxmatch)
     character(len=:),allocatable :: input_line(:)
     character(len=:),allocatable :: output_line
     character(len=:),allocatable :: expression
     logical                      :: match
     integer                      :: stat
     integer                      :: i
     logical                      :: BRE
        ! The /etc/passwd file is a colon-separated file that contains the following information:
        !
        !     User name.
        !     Encrypted password.
        !     User ID number (UID)
        !     User's group ID number (GID)
        !     Full name of the user (GECOS)
        !     User home directory.
        !     Login shell.
        !
        BRE=.true.
        if(BRE)then  ! BRE (Basic Regular Expression)
           expression= '\([^:]*\):*\([^:]*\):*\([^:]*\):*\([^:]*\):*\([^:]*\):*\([^:]*\):*\([^:]*\):*.*'
           call regcomp(regex,expression,status=stat)
        else         ! ERE (Extended Regular Expression)
           expression= '([^:]*):*([^:]*):*([^:]*):*([^:]*):*([^:]*):*([^:]*):*([^:]*):*.*'
           call regcomp(regex,expression,'x',status=stat)
        endif

        if(stat.ne.0)then                                        ! if RE did not compile report error
           write(*,*)'*regcomp* ERROR:',regerror(regex,stat)
           stop 1
        endif

        ! simulate /etc/password file in array, with common aberrant input lines included
        input_line= [character(len=128) ::                                     &
        "doeqj:xxxxx:1001:200:John Q. Doe:/home/doeqj:/bin/tcsh: and more",    &
        "doeqj:xxxxx:1001:200:John Q. Doe:/home/doeqj:/bin/tcsh: and more:",   &
        "doeqj: :1001: :John Q. Doe:/home/doeqj:/bin/tcsh:",                   &
        "doeqj:xxxxx:1001:200:John Q. Doe:/home/doeqj:/bin/tcsh:",             &
        "doeqj:xxxxx:1001:200:John Q. Doe:/home/doeqj:/bin/tcsh",              &
        "doeqj:xxxxx:1001:200:John Q. Doe:/home/doeqj",                        &
        "doeqj:xxxxx:",                                                        &
        "doeqj:xxxxx",                                                         &
        "doeqj:",                                                              &
        "doeqj",                                                               &
        ! the RE shown needs the field to have at least one character
        ! which should be replaced first, but not shown in this example
        ": : : : : : : : : : : : : : :",                                       &
        ": ::",                                                                &
        "" ]

        do i=1,size(input_line)
           match=regexec(regex,input_line(i),matches)            ! generate the matches array using the compiled RE

           write(*,'(a)')repeat('-',80)                          ! put out a number line
           write(*,'(a)') input_line(i)
                                                                 ! replace \n lines
           call regsub(input_line(i),matches,'username="\1" &
           &password="\2" UID="\3" GID="\4" name="\5" &
           &home="\6" shell="\7" ',output_line)
           write(*,'(a)') output_line

           if(i.eq.1)then                                        ! show other examples of formatting for first entry
              call regsub(input_line(i),matches,&
              & 'The username for \5 is "\1"',output_line)
              write(*,'(a)') output_line

              call regsub(input_line(i),matches,&
              & 'username "\1" has UID=\3, GID=\4 &
              & and default shell "\7"',output_line)
              write(*,'(a)') output_line
           endif
        enddo

        call regfree(regex)

     end program demo_regsub