#!/usr/bin/tclsh
#script to append data to file safely.
set fnametarget [lindex $argv 0]
set fnametemp [expr {[expr [string length [lindex $argv 2]] > 0]  ?  [lindex $argv 2] : "/tmp/tmpfile.[clock format [clock seconds] -format %s]"}]
set pattern [lindex $argv 1]

proc writetoreplacement {lst fn {dbg 0}} {
set i 0
set toohandle {}
                        if {[catch {set toohandle [open $fn "w"]} err]} {puts "Error: In procedure writetoreplacement -- $err." ; return -1}
                        for {set i 0} {$i < [llength $lst]} {incr i} {
                            puts $toohandle [lindex $lst $i]
                            if {$dbg > 0} {puts "Wrote [lindex $lst $i] to descriptor $toohandle"}
                        }
                        close $toohandle
                        return $i
}
                            
                             

#main
if {![string length $fnametarget] || ![string length $pattern]} {puts "Error: Please provide -- 1. filename, 2. regexp to find in file, 3 (Optional) name of temp file." ; exit}
if {[catch [file copy -force $fnametarget $fnametemp] err]} {puts "Error: Unable to copy file $fnametarget to $fnametemp -- $err" ; exit}
if {[catch {set fd [open $fnametarget "r"]} err]} {puts "Error: could not open target file $fnametarget." ; exit}

#file is copied and opened with descriptor structure at $fd. read file by line looking for pattern.
set count 0
set rep {}
set linelist {}
set tmpline ""
 
while {[gets $fd line] > 0} {
       incr count
       lappend linelist $line
       if {[regexp $pattern $line]} {
           puts -nonewline "\nFound pattern $pattern at line # $count. Please enter appending string: "
           gets stdin rep
           if {![string length $rep]} {continue}
           set tmpline [lindex $linelist [expr $count - 1]]    
           append tmpline $rep
           set linelist [lreplace $linelist [expr $count - 1] [expr $count - 1] $tmpline]
           puts "Committed change at $count = [lindex $linelist [expr $count - 1]]" 
       }
}

puts "Committing...."
after 1000
writetoreplacement $linelist $fnametemp
if {[catch [file copy -force $fnametemp $fnametarget] err]} {puts "Error comitting changes: $err"; exit}
file delete -force $fnametemp