Many systems offer the ability to open a file for writing, such that any data written will be appended to the end of the file. Further, the file operations will always adjust the position pointer to guarantee the end of the file, even in a multitasking environment.

This feature is most useful in the case of log files, where many jobs may be appending to the log file at the same time, or where care must be taken to avoid concurrently overwriting the same record from another job.



Task

Given a two record sample for a mythical "passwd" file:

 Write these records out in the typical system format.
 Ideally these records will have named fields of various types.
 Close the file, then reopen the file for append.
 Append a new record to the file and close the file again.
 Take appropriate care to avoid concurrently overwrites from another job.
 Open the file and demonstrate the new record has indeed written to the end.

 Source record field types and contents.


account
password
UID
GID
fullname,office,extension,homephone,email
directory
shell


string
string
int
int
struct(string,string,string,string,string)
string
string


jsmith
x
1001
1000
Joe Smith,Room 1007,(234)555-8917,(234)555-0077,jsmith@rosettacode.org
/home/jsmith
/bin/bash


jdoe
x
1002
1000
Jane Doe,Room 1004,(234)555-8914,(234)555-0044,jdoe@rosettacode.org
/home/jdoe
/bin/bash


 Record to be appended.


account
password
UID
GID
fullname,office,extension,homephone,email
directory
shell


string
string
int
int
struct(string,string,string,string,string)
string
string


xyz
x
1003
1000
X Yz,Room 1003,(234)555-8913,(234)555-0033,xyz@rosettacode.org
/home/xyz
/bin/bash

Resulting file format: should mimic Linux's /etc/passwd file format with particular attention to the "," separator used in the GECOS field. But if the specific language has a particular or unique format of storing records in text file, then this format should be named and demonstrated with an additional example.

Expected output:

Appended record: xyz:x:1003:1000:X Yz,Room 1003,(234)555-8913,(234)555-0033,xyz@rosettacode.org:/home/xyz:/bin/bash

Finally: Provide a summary of the language's "append record" capabilities in a table. eg.


 Append Capabilities.


 Data Representation

 IO
Library

 Append
Possible

 Automatic
Append

 Multi-tasking
Safe


 In core 
 On disk


 C struct 
 CSV text file 
 glibc/stdio 
 ☑ 
 ☑ 
 ☑ (Not all, eg NFS)

Alternatively: If the language's appends can not guarantee its writes will always append, then note this restriction in the table. If possible, provide an actual code example (possibly using file/record locking) to guarantee correct concurrent appends.




include ..\Utilitys.pmt
 
def ltos    /# l -- s #/
    "" >ps
    len for get
        string? not if
            number? if
                tostr
            else
                ltos
                "<ls>:" swap "</ls>" chain chain            
            endif
        endif
        ps> swap chain ":" chain >ps
    endfor
    drop
    ps>
enddef
 
 
def stol    /# s -- l #/
    -1 del
    ":" xplit
    "<ls>" find 1 + snip
    "</ls>" find snip 1 del
    rot len >ps rot ps> set swap chain
enddef
 
 
( "jsmith" "x" 1001 1000 ( "Joe Smith" "Room 1007" "(234)555-8917" "(234)555-0077" "jsmith@rosettacode.org" ) "/home/jsmith" "/bin/bash" )
( "jdoe" "x" 1002 1000 ( "Jane Doe" "Room 1004" "(234)555-8914" "(234)555-0044" "jdoe@rosettacode.org" ) "/home/jdoe" "/bin/bash" )
 
swap
 
"passwd.txt" var file
 
file "w" fopen var f
ltos 10 chain f fputs
ltos 10 chain f fputs
f fclose
 
( "xyz" "x" 1003 1000 ( "X Yz" "Room 1003" "(234)555-8913" "(234)555-0033" "xyz@rosettacode.org" ) "/home/xyz" "/bin/bash" )
 
file "a" fopen var f
ltos 10 chain f fputs
f fclose
 
file "r" fopen var f
true while
    f fgets number? if
        drop false
    else
        stol ? true
    endif
endwhile
f fclose