Question

I want to find a pattern in a file, but the pattern can have several forms.
Here is the code :

while {[gets $thefile line] >= 0} {
     for {set nb_table 1} {$nb_table<$count_table} {incr nb_table} {
          if { [regexp {pattern_$nb_table} $line] } {
          puts "I found one !"
          }
     }
}

the var $count_table is known, catched before on a on a other procedure.

If i do a puts of pattern_$nb_table in the for loop i got the name of all tables and that’s good, but I never have I found one! printed out (sure i want to be another process but it is not the subject). Why I never go in the if? My file contains the pattern : pattern_1 pattern_2 .....

Answer 1

The problem is that the variable is not being substituted into the regular expression (the {…} disable all immediate substitutions). This is a situation where you’d use (putting the variable name in braces just for clarity, and putting the pattern in double quotes for highlighting only):

if {[regexp "pattern_${nb_table}" $line]} { ... }

Except that if I was looking for a string that simple, I’d try to use string first or string match:

if {[string first "pattern_${nb_table}" $line] >= 0} { ... }

if {[string match "*pattern_${nb_table}*" $line]} { ... }

Both of these are faster than regular expression matching, provided you’re doing something simple. If the rest of the real pattern is a regular expression, only regexp will do. Of course.