# -*- tcl -*-

# hello world
# print a simple string on stdout
puts "Hello World"

# argv
# access command line parameters (no segmentation fault accepted, nor silent exception, so some languages must explicitly check the presence of the argument)
puts [lindex $argv 0]

# env
# access environment variable
puts $env(HOME)

# test file exists
# return exit code error (non zero) if a file does not exist
exit [expr ![file exists /etc/mtab]]

# test file readable
# return exit code error (non zero) if a file is not readable
exit [expr ![file readable /etc/mtab]]

# formatting
# print integers in a simple formatted string
set a 1; set b 2; puts "$a + $b = [expr $a + $b]"

# system
# call an external program and check the return value
if {[catch {exec false}]} {puts stderr "false failed"}
exec echo >@ stdout done


# sed in place
# remove #-comments from a file (modifying the file, i.e. in place)
set f [lindex $argv 0]
set fd [open $f r]
regsub -all {#[^\n]*\n} [read $fd] {} contents
close $fd
set fd [open $f w]
puts -nonewline $fd $contents
close $fd


# compile what must be
# find and compile .c files into .o when the .o is old or absent
proc doit {dir} {
    foreach f [glob -nocomplain $dir/*] {
        if [file isdir $f] {
            doit $f
        } elseif { 
            [regsub \\.c$ $f .o o] && !( 
               [file exists $o] && 
               [file mtime $o] > [file mtime $f]
            ) } {
                puts "compiling $f to $o"
                exec gcc -c -o $o $f
        }
    }
}

doit .


# grep
# grep with -F -i -h handling, usage, grep'ing many files
set i 0
set F 0
set ind 0
set usage 1
foreach s $argv {
    if { "$s" == "-i" } { 
        set i 1 
    } elseif { "$s" == "-F" } { 
        set F 1 
    } elseif { "$s" == "-h" } { 
        incr usage
    } {
        incr usage -1
        break
    }
    incr ind
}

if $usage {
    puts stderr {usage: grep [-F] [-i] regexp [files...]}
    exit 1
}

set re [lindex $argv $ind]
incr ind
set files [lrange $argv $ind end]

if $i { set re (?i)$re }
if $F { set re (?q)$re }

set nb [llength $files]

proc grep { prefix fd re } {
    while {[gets $fd s] >= 0} {
        if [regexp $re $s] { puts $prefix$s }
    }
}

if { $nb == 0 } {
    grep "" stdin $re
} {
    set prefix ""
    foreach f $files {
        if { $nb > 1 } { set prefix $f: }
        set fd [open $f]
        grep $prefix $fd $re
        close $fd
    }
}